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Thursday, 12 April 2018

Repairing a Stihl 024 (or 026) with Huztl parts

An old 024 gets repaired with Huztl parts and a compression problem is resolved

A few weeks ago I found the badly battered and incomplete carcass of a fairly small, old chainsaw in the metal bin at Mt Nebo tip. Because it looked like a Stihl (it had an inboard clutch) and a professional model (it had a metal crankcase visible from underneath), I brought it home in the cargo bike to see if it was any use. I was busy for the rest of the day but by the end of the afternoon, our son Jasper had dismantled the saw and identified it as a Stihl 024: the smaller precursor to the 026 (later the MS 260, then superseded by the MS261) which is a very popular and durable small, professional grade saw. The 024 was produced from 1982-1994, 2.6HP from 41.6ccs. This saw could be 30 years old or more. 
Once it was in pieces, we could see the piston had a big score on the exhaust side - a common way for a chainsaw to fail, often from overheating caused by unmixed fuel or too lean a fuel-air mixture. 
The big score on the little piston, exhaust side
This is probably why the saw had been dismantled and discarded. There was a hole in the oil tank - probably from being thrown into the bin. Lots of parts were missing: carby, air filter, bar and chain, all the covers including clutch cover, rewind starter, cylinder cover, air filter cover. There was some fairly deep corrosion in the metal chassis around the clutch - a common problem when a saw isn’t quickly cleaned after cutting palm trees (and perhaps some others). 

Worth repairing

It would be easy to conclude that this saw wasn't worth fixing (someone clearly already had), but the cheap and easy supply of non-genuine parts makes solidly built saws like the professional Stihls very much worth repairing for frugalistas like me. 
My confidence in fixing this type of chainsaw has been greatly improved by watching Andy Reynolds' videos on chainsaw repair, and making a Huztl 036
We made a list of what was missing, and made an order of non-genuine parts from Huztl. The parts cost about $130 to fix the saw (but I also bought some spares - I like to have in stock what I expect to need). This seems very good to me - consider that the current comparable Stihl model, the MS241, costs AU$1350 new. 
Everything went together fine, but there were a few lessons for me on the way. 

Oil tank hole

I cleaned the oil tank carefully: first with solvent (mineral turps), then methylated spirits, then degreaser. I used some thick epoxy resin to fill the hole. This has worked fine. 
Epoxy glue sealing the hole in the oil tank

Air filter

Something about the Huztl air filter and filter cover wasn’t right. As supplied, the filter cover would slip on fine, but would keep popping up while the saw was in use, seemingly because of pressure from my right hand. This wasn’t okay while working - having to keep pushing it back down. For some reason, the peg on the back of the air filter was too short to securely latch into the filter cover lock.  
I fixed this with a piece of steel nail and (one of my favourite fixing tricks) string and epoxy resin. I found a nail that fit snugly into the slot in the air filter peg, glued it in with epoxy, then wrapped the peg and nail in string with epoxy. A layer of resin over the string gave a nice smooth finish. This has worked perfectly for quite a few hours of work so far. 
See the extended peg on the air filter, to give the filter housing a positive latch-on

Clutch drum and oil pump

The old clutch drum was worn, and the new clutch drum needed modifying to fit my old 024. 
The older models of 024 and 026 used a crude but effective oil pump arrangement which is now superceded. More modern saws only pump oil into the bar when the chain is running (actually when the clutch drum is turning), but this old 024 has a simpler setup that pumps oil whenever the motor is running. A short steel worm drive fixed to the crankshaft turns a gear on the pump unit. This is wasteful of bar oil if you leave the saw idling for long periods - which isn’t a good idea anyway, as idling causes extra wear of the clutch drum needle roller bearing. I bought the parts to convert it to the modern system, but decided not to use them yet: the old system works fine, I’m using free old fryer oil, I don’t yet know how to get the steel worm drive off the crankshaft, so the cheapest good-enough option is to leave it all alone. 
This is the oil pump on the old type continuous oiler, behind the clutch
024 and 026 saws with the old continuous oilers use a clutch drum that is just deep enough to fit over the centrifugal clutch. The modern ones have a deeper drum with a rim that extends past the clutch (on the motor side), where there is a little notch that engages with the wire quill that drives the pump. When the clutch drum starts to turn and drive the chain, it also drives the pump by pushing the wire around. 

The clutch drum I bought was of the modern wide type (I don’t think Huztl sells the old narrow type). This is too deep for the old style saws: the drum edge rubs on the oil pump. I wore a bit of a groove into my oil pump (without causing any problems) before I realised I had the wrong clutch drum width. 
You can see the groove in the oil pump from the over-width clutch drum, centre photo, showing some brass
Fixing the clutch drum was simple enough, using the bush engineering technique of angle grinder and lathing in place. I simply reversed the clutch drum on the crankshaft where it could spin freely, and held an angle grinder up to it to grind and spin it at the same time. I ground until the oil pump quill notch was gone, chamfered off the sharp edges, then reversed and installed the clutch drum as normal. Here's a little video how:

Cylinder squish and compression

I had noticed that the old cylinder was probably useable: there was a bit of a score on the exhaust side, but only below the port. However I installed a new Huztl piston and cylinder. The saw ran and cut, but I felt like something wasn’t right. The saw seemed to be weak under power, had a lag on throttling, and most of all: pulling the starter cord was too easy. The motor would spin over too smooth and fast, without the noticeable lumpiness of the compression strokes. It seemed like the compression was low. 
Looking at the Stihl specs for the 024, I could see that the 024 had both a shorter stroke and smaller bore than the 026, by 2mm each way. 
But I saw that Huztl sold one crankshaft that was supposed to fit both 024 and 026. That caused me to wonder if the Huztl cylinder - which would presumably fit the Huztl crankshaft - was made for the longer stroke. If so it would probably be 1mm too tall for the 024, which would give it low compression. 
I tried a "squish test" on the Huztl cylinder. I poked a piece of solder in thru the spark plug hole, right to the back of the cylinder, turned the crank over one revolution, then measured the thickness of the squashed end of the solder. I got 1.4mm (I needed to find some thick solder), which seemed big compared to what I could find online. 
Then I swapped cylinders, re-installing the original Stihl cylinder (after cleaning up inside pretty carefully). On these saws, a cylinder swap is surprisingly easy, taking only a few minutes. 
On the Stihl cylinder, the squish test measured 0.9mm, which was 0.5mm shorter than the Huztl (some online sources proposed that about 0.5mm squish was good). This was consistent with my measurements of the 2 cylinders: the Huztl measured 61.9mm from base to squish ring (flat area around perimeter of head), and the Stihl measured 61.4mm. 
Measuring the depth of the cylinder with vernier caliper. Huztl cylinder is the dark one on left, Stihl is the light coloured one on right
Looking into the 2 cylinders, you can see the "squish ring": the bright circle of flat machined metal around the cylinder crown, right at the bottom (which is really the top)
When I started the saw with the Stihl cylinder, I found a different saw. It was lumpy to pull over, and when it started, the idle speed was so high I had to back off the idle screw several turns (it had been almost all the way in). Cutting wood, it had heaps more power. It was now a really sprightly little saw. 
I’m hoping the old Stihl cylinder goes well for a long time. I feel the score below the port shouldn’t cause harm - the piston and rings need to go past all the ports, which are much bigger than a little score. If/when I need to replace the cylinder, if I’m still using the old crankshaft, I can restore good compression by shaving a little off the Huztl cylinder base: this can be done on a lathe (first machining a spigot to fit inside and hold the cylinder), but I imagine it could also be carefully done with a file. 

Chain and bar

Liking short bars (and son Jasper having a very satisfactory 13” bar on his 026), I made a 13” bar from a Holzfforma 16” bar from Huztl; this cost approx AU$10 when a genuine Stihl is about $75. My post on shortening bars can be found here. I bought some long .325” chains from Huztl, and cut and shut them to 56 links for the short bar. I made 3 chains to rotate with the sprocket: all to be replaced together when the chains are worn out. 

The working saw

With its short bar, good compression, and compact, light motor, my 024 has become my favourite saw for thinning and pruning in the family forest at Stanthorpe, where it has done a lot of work cutting small White Cypress trees (which badly overcrowd the forest there). Once warmed up, it starts first pull over and over all day (I do a lot of stop/start). The continuous oiler certainly keeps the chain oily - if I was paying for oil from the shop I’d consider swapping over to the clutch drum-driven oil pump. It is very economical with fuel: a tank full will thin for over an hour. I greatly value the saw's lightness when lifting it up and down to prune small branches off the trees, and bending over to cut them off near the ground.  
In conclusion, for light work, the old 024 is a great little saw. Robust, repairable, light. Worth fixing!


Sunday, 8 April 2018

Xiongda 2-speed hub motor breakdown: slipping magnets

Re-gluing the magnets on a motor with oil lubrication
This week I had a new type of electric bike hub motor breakdown. The Xiongda 2-speed rear hub motor on my 26" wheeled bike started to make a harsh scraping sound - similar to a disc brake with pads worn to the metal. The sound only came when when power was applied against resistance (like going uphill), and the bike felt like it was losing power. Stopping at the roadside, I found I could stop the rear hub-motor wheel completely with the brake, run the motor with the throttle, and hear the motor turning inside the stationary wheel, making the awful scraping sound.
Here's a short video of what happened when I powered the rear wheel, off the ground. First it runs in low speed and I apply the brake while leaving the throttle on, then I do the same in high speed:

The sound could be made in high or low motor speed. Limping the bike home (up the mountain…) I found I could run the motor on 3/5 power without it slipping and scraping.
I dismantled the motor, expecting a sheared key on the freewheel plate, or some other sort of freewheel problem.
Here's the tool I made to unscrew the motor side plate
After checking it all carefully, and trying a new freewheel plate which didn’t stop the sound, I noticed some of the magnets in the magnet drum were a fraction out of alignment with the drum edge. I found I could slip the individual magnets out with gentle levering. Evidently the magnets had come unglued and were spinning inside the drum, not turning the drum.
Here are the magnets slipped out of their places, but still holding onto the drum with magnetism
This motor is one of 2 XD 2-speed hubs I’ve put Automatic Transmission Fluid (ATF - a light oil) into, in the hope of improving cooling of the copper coils on steep climbs. It also makes the motor sound rather smoother - the XD 2-speed is a pretty noisy motor, with its complex gears and freewheels. As I’ve discussed elsewhere in my blog, the coils of a hub motor have trouble losing heat when labouring. To escape from the motor windings, heat must travel either by conduction through the laminated core to the axle, or by radiation from the coils and core to the magnet drum, then radiating again to the hub case - either way is very inefficient. Adding some ATF provides good lubrication throughout the hub, and the flow of fluid can be expected to carry some heat from the coils to the case. The drawback is that some leakage of oil can be expected through the axle bearings and elsewhere, especially if the bike is laid on its side. I haven’t yet concluded whether the ATF is making a significant difference to motor temperature but the motors certainly run quieter.
I’m not sure what effect the ATF has had on the magnets coming loose in this case. Clearly however, once they came unglued, the oil would have made it much easier for the magnets to slide around inside the drum. Perhaps without ATF the magnets would stay in place without glue. But did the ATF have a role in ungluing them? This motor has had ATF in it for a few hundred kilometres and a few months (it's my less-used bike), but I have another XD motor which has had ATF for 1000 or 2000km and a few months, without trouble.
The magnet drum has 20 curved high-strength magnets arranged around inside the drum cylinder, that rotate around the 18 poles of the armature. Before removing them, I marked the magnet ends with alternating patterns of file grooves: 1 groove and then 2 grooves. This represented the alternating polarities of the magnets, so I could replace the magnets with the right orientation, polarity and pattern.
To repair the motor, I needed to glue the magnets back into the drum. The biggest challenge was cleaning the oil off the magnets and the drum. I used turps, metho and degreaser in turn.
Here are the magnets drying on a strip of sheet metal after cleaning - you can't just put them in a box or they'll smack together
I left the 2 sealed bearings in the drum, and took care not to get solvent or degreaser into them. After cleaning, I sanded both surfaces, and ground a bit of roughness into the drum surface with a die grinder and disc. My main concern is that there be enough friction to prevent sliding.
The magnets being glued back into place with epoxy. Note the file marks on the magnet edges, so I could replace them in the right orientation and order.
I used runny epoxy resin (like is used for fibreglassing) to glue the magnets in. The magnets hold themselves into the drum very firmly with their magnetism - no need for clamps. I left all magnets a little proud of the drum, and aligned them together by pressing the drum down onto a flat surface.
I recognise that the epoxy will weaken when the motor is hot, but the glue's job is to resist shear forces - stopping the magnets sliding around inside the drum again - so even if it was softened by the heat it should do its job.
Installed back on the bike, the motor is working perfectly again. Of course I can't be sure until it's done 5000km like this...

Tuesday, 27 February 2018

Reversing a Bafang 8Fun BPM motor

How to modify a BPM hub motor to drive in the reverse directionUsing 2 BPM front motors to drive a cargo trike

A friend recently asked me to modify a BPM motor to run backwards. The motor was one of a pair to be installed on the front of a Zeitbikes cargo trike (a Chinese box trike - I don't know if they are sold under that brand any more). 
These box trikes are very heavy, not stable at speed or on uneven surfaces, and this one was to live at Highgate Hill (Brisbane) and would need to do a lot of climbing with loads. 
An attempt had been made to drive the trike with a single rear motor, but this had proven to have inadequate torque at the low speeds the heavy trike was able to achieve safely. 
Here's the trike with a single rear hub motor: too fast, not enough torque
The frame was not suitable for installation of a mid-drive motor, having extra tubes around the bottom bracket.
The new plan was to use 2 less powerful, higher torque, lower speed motors in the front wheels, one on each side of the cargo box. 
The Zeit trike uses hydraulic disc brakes on the front wheels (which work very well), with calipers on the box side of each wheel, so making the left side wheel turn opposite to normal was necessary so that the brake disc could be on the right hand side. 

Reversing the mechanics

It is relatively easy to make the internal motor of a geared hub to run backwards, just by the way it’s connected to the controller - as many of us find by accident when first wiring them up. However when the internal motor runs backward, it doesn't turn the hub backward, you just hear a whizzing inside a stationary hub. This is because geared motors use a freewheel, the main purpose of which is to allow the bike to coast along without resistance if the motor is not powered. In order to change the rotation of a geared motor, the freewheel needs to be reversed mechanically, as well as reversing the motor electrically. 
If you've opened a geared hub motor, you've seen the freewheel. It's a steel disc that mounts onto the main motor shaft thru its centre (with a slot and key to lock it in place). 
Here's the freewheel straight out of the motor
Here's a BPM freewheel with one gear removed
The freewheel disc carries the 3 nylon planet gears on 3 stub shafts attached near its perimeter. The "freewheel" part of the freewheel is 3 (not visible) sprung rollers that allow the circular plate of the unit to turn one way around the centre boss but not the other. To reverse the motor, we need to rearrange the freewheel so that the rollers allow movement in the opposite direction from normal. 
Reversing the freewheel involves: 
- removing the 3 stub shafts
- removing 3 small rivets that hold the freewheel plate together
- dismantling the freewheel body
- reassembling the body with the centre boss and the 3 stub shafts reversed to the other side of the plate. 

Step by step

First the 3 nylon gears were removed from the freewheel disc. This is easily done by removing the circlips from the stub shafts, I used circlip pliers (whose tips open when you squeeze the handles) and some rag around the job to catch any flying circlips. The nylon gears, along with their sealed bearings, slide off pretty easily. 
Freewheel without gears, stub axle side
Freewheel other side, with centre boss sticking up in the centre
Next job was to punch out the stub shafts, the serious part of the job. It's important to be very careful: you can't afford to have any impacts on the outside end of the stub shafts, or you risk damaging the circlip groove and making reassembly difficult. 
I have ground off the short riveted end of the stub shafts in the past, to open a freewheel and repair the sprung rollers (link). But this loses a lot of metal from the rivet head, making reassembly  difficult. Having recently been riveting a few chainsaw chains, it occurred to me that the stub shafts could be un-riveted the same way as a chainsaw chain is unriveted: by punching. When you punch apart a chainsaw chain rivet, you only lose a small ring of metal from the perimeter, leaving enough metal in the rivet usually to be able to peen and re-use the rivet to make a chain loop. 
Here is the freewheel on the anvil, having a stub shaft punched out. 
Suitable punch on top of riveted axle end, the stub axle is inside the old nut below
The freewheel plate is supported by large nuts, bigger than the flange in the middle of the stub shaft. I used a punch a little smaller than the rivet head, driven by a 1.2kg blacksmithing hammer. 
Here's the first stub axle punched out
Once the stub shafts have been driven out, 3 small rivets hold the laminations of the freewheel plate together. These are punched out, like the stub shafts but with a smaller punch. 
Once all the rivets are punched out, the 3 plates of the freewheel come apart - I carefully kept things together as much as possible. The centre boss (which fits onto the main motor shaft) is then lifted out and turned over to be re-inserted.
Axles punched out, small rivets punched out, now the first plate can come off and reveal the freewheel rollers in their tapered slots
Here the centre boss is lifted out. The small steel rings at rear are the old rivet head rims, left on the punch after punching the axles out
Installation requires the freewheel rollers to be pushed back into their spaces to let the centre boss in. You'll work it out. 
Once the centre boss is re-installed, the freewheel plates need to be riveted back together, with both the small rivets and the stub shafts. The stub shafts are inserted into the opposite side of the freewheel plate from where they came. With the centre boss reversed and the stub shafts reversed, the whole freewheel unit looks just the same as it did before being dismantled - the only difference being the plate freewheels in the opposite direction around the centre boss. 
Be careful! Don't reassemble the whole thing the same as it started. I liked having a spare freewheel unit on the bench to check I was doing things right.
Here's the freewheel reassembled, with heads peened onto the axle ends and small rivets with a ball peen hammer 

Reversing the electrics

The internal motor is very easily reversed electrically if a sensorless controller is being used: simply swap any 2 of the phase wires and the internal motor will reverse. With a sensored controller (which I don't usually use), it takes more trouble: swap 2 phase wires, then try different arrangements of the 3 coloured sensor wires (leave the red and black alone). This has taken me some time in the past. 

It works!

The motor I reversed this way now works perfectly, in reverse. It and a normal non-reversed motor have been installed as the 2 front wheels of the box-trike. The motors are Bafang/8FUN BPM 500w code 13 front motors, laced into 20” rims. 
Here's the 20" wheel where a 24" was
The trike was manufactured with 24” front wheels, but we switched to 20” rims to reduce speed and increase torque - it worked very well and the trike runs fine with the smaller wheels. They are powered by 2 GreenBikeKit.com CON121 controllers, with a single thumb throttle wired into the throttle connections of both controllers in parallel. Both controllers are powered from one 36V battery, using 15/45A Anderson connectors. 
The box trike on a test ride, climbing a hill with the new motors
If you want to buy a spare freewheel unit before you start knocking the original apart (like I did), check that you get the right sort: there are 2 different freewheel types in BPM motors. Have a look at my BPM page for more info. 
The customer has been very happy with the trike, using it daily in hilly Highgate Hill, Brisbane. It has loads of torque, and powers up to about 20km/h. This is about as fast as these box bikes should go: their non-independent front steering - turning the whole box to steer - is very vulnerable to any bump on one side pushing that wheel back and forcing a turn. To me, the relatively high rider position also feels unstable when the trike tilts to one side due to the road camber or crossing a slope. 

The promise of 2 drive wheels

I think the 2-wheel drive system we installed on this trike has a lot of promise for cargo cycles. I know that a cantilevered axle (where the wheel is attached only on one side, like a car wheel, or a wheelchair wheel) appears a more elegant way to put wheels on each side of a vehicle. But using normal bike wheels bolted into dropouts on each side has many practical advantages. Most importantly: there are heaps of wheels like this available, in all sorts of formats: electric hubs of various types and speeds, disc braked, etc.. 
Imagine how much help some electric assistance would be to these hard-working charcoal makers:
Phnom-Penh charcoal delivery trikes (sorry I have no credit for this photo)
I quite fancy some sort of delta, recumbent cargo trike format, like this:
(sorry, no photo credit again)

Monday, 8 January 2018

Fixing a wobbly Dahon frame hinge

How to fix a steel Dahon frame hinge that wobbles, even when tightened
The closed and clamped hinge. Grab this and push it up and down to see if it wobbles
Between our family and our friends, we use Dahon folding bikes a lot. My heavily modified (including electric hub motor) Dahon Boardwalk has done around 20,000km of heavy riding, carrying my 80kg self plus panniers on our steep (and some rough) mountain roads. Our friend Bradley also does heaps of distance on his Dahons, mostly 2 Speed TRs (one is also electrified). It is tremendously useful to us to have folding bikes, especially living on a mountain where getting a lift in a friend’s car can save a lot of time and effort.
On the other hand, Dahons have also caused us a lot of bike mechanic grief. It seems to me that the culture of marketing and “innovation”, with almost annual “new models”, means that the designs aren’t refined, but are simply shuffled. All of the Dahons I’ve known have had serious design flaws, providing fairly major bush engineering challenges to keep them on the road: splitting seat tubes, frame and steerer hinge problems, headset problems (especially with threadless). We’ve only bought steel-framed Dahons, very conscious of the repairability of steel, as well as how fragile and unreliable aluminium frames are in diamond frames, let alone under the greater stresses of folding bike geometry.
We’ve had to repair nearly all the frame hinges that have done reasonable distances. This is what happens:
Even with regular tightening of the hinge adjusting bolt, frame hinges tend to eventually get a wobble. This is an up and down wobble, found by grasping the hinge of an unfolded bike, and lifting it up and down while holding the rest of the bike down.
What seems to be the problem is that the mating faces of the hinge are manufactured flat, so any tiny wear at top and bottom allow a small rocking movement, regardless of how tight the hinge is. A little rocking brings huge pressures on the surface at top and bottom and leads to more wear, making more wobble even when tightly adjusted. Once worn slightly convex, clamping pressure only acts on the middle of the hinge faces. What is needed is to spread the clamping pressure back to the top and bottom of the faces.
On our steel Dahon frames, we have found a remarkably simple remedy: laying a very small pad of stick welding at the top and bottom of the male mating face, filed smooth (I use a 2.6mm mild steel rod, at 130A). This creates pressure points at the very top and bottom of the hinge mating face, and leaves a slight gap in the middle - where the faces were rocking. The raised pads are perhaps a little more than 1mm high after filing.
The welded pads are on the left side hinge face, top and bottom. At the top of the right side face you can see the worn area which has caused the wobble
Before welding, the hinge clamp is undone by removing a small circlip from a vertical pin and removing the pin so that the clamp can be folded out of the way. 
What this achieves is to distribute the hinge clamping pressure onto 4 discreet points on the perimeter of the hinge faces: top and bottom welded pads, hinge pin on one side, clamp on the other.
I’ve done this repair on (I think) 4 Dahon frames, with excellent results.


Thursday, 28 December 2017

Starting a top bar bee hive

Today I started my first top bar bee hive. This has been coming for some time, and taken a lot of thinking, planning and building. Now to see if it works!
The brown top bar hive is on top of (and part of) the white 10-frame hive. The queen excluder is below the top white (brood) box.

Why top bar?

There’s been a long lead up to this: Erika and I kept bees for years (I started by catching a swarm in Abney Park Cemetery, Stoke Newington, London with my mate Gomez in 1985), until family life overwhelmed and we gave our hives away. A couple of years ago I got sucked back into beekeeping when Erika’s mother and brother started hives in Stanthorpe. They bought 10 frame, full depth boxes, so I ended being the only person who knew how to do bees, wasn’t scared of stings, and was tall enough and strong enough to lift the boxes.
10 frame full depth boxes (supers) are very heavy things, when full of honey. They need to be lifted high: onto a hive of up to 4 boxes (sometimes more), which is already on a stand to keep the hives above the grass and away from toads etc.. Most times you go to do anything with the bees, it starts with climbing up and lifting a 40kg+ box full of sting-ready bees down off the top. I’m finding this is at the limit of my strength, which I don’t think is a good idea. I’m also squashing a lot of bees, especially when replacing heavy boxes onto crowded hives. This feels bad and gets the bees cranky.
There is no way my late-70s mother in law with arthritic fingers is going to be doing anything much at all with these he-man hives, which is a real pity. My strong but short brother-in-law is also not able to do much work on his hives when the honey is flowing. Both of them miss the pleasure of learning about the bees, the hives get neglected between my visits, and I end up responsible.
So I’m feeling pretty strongly motivated to find a way of keeping bees that doesn’t involve frequent heavy lifting from ladders.
Top bar hives fix this. They use a single box - one level. They don’t use supers (unless you get clever), so nothing heavier than a single comb (equivalent to a single frame) needs to be lifted (unless perhaps the hive has a heavy lid). They are managed by frequent, low-intensity visits, instead of periodic major exercises. I’m hoping they are suited to a determined old lady who has a fascination with nature.

Home made

I also like the whole top-bar style. Especially that I can make every part of the hive myself, from wood we have grown and milled, with my existing tools. The top bars can be sawn from off-cuts which would otherwise be firewood.
The hive I started today has been made in my workshop at Mt Glorious, and brought out to Stanthorpe this week. I’ve made 2 nucleus hives (small hives to start a new colony in). One has an open bottom and is designed to fit on top of a standard 10-frame box - that’s how I’m planning to start the hive with a colony of bees.
This brown top bar hive has no bottom, so it's open to the 10-frame brood box below it. The lid has a layer of pine boards on top of the top bars for insulation, then a corrugated iron roof.
The other box has a bottom and is planned to be self-contained, housing the new colony when it is separated from the 10-frame hive.
This is the top bar nucleus hive with a bottom, intended to house the independent colony when it's separated from the mother hive. 
The boxes are made from un-treated slash pine boards I cut years ago with a chainsaw mill, but which have been slightly attacked by borers (because I didn’t treat the wood with borax after milling), so the wood can’t be used for furniture. If it works for a few years as bee hives, I’ll be pleased - and in the dry Stanthorpe climate I expect them to last fine. The boxes have one coat of water-based paint (from the tip).

What design?

I’d like to benefit from other people's expert experience, but it took some time to decide on a design - I even started and then abandoned some bars and a box after deciding they weren’t the way to go (bars too short and box too deep).
My main concern with hive design is to avoid combs breaking off on hot days, due to being too deep and narrow. I’ve used the top bar design of Les Crowder, whose excellent youtube video is very helpful, and whose book I bought. Les uses bars 20” long, which I metricised to 505mm. I was a bit torn between Les’s size and the “Standard top bar” size of 19 1/2” (495mm), but if I ever want to I can easily cut mine down to standard length. I’ve made the box sides from 250mm wide boards, tilted at 60* to horizontal.
To make the top bars, I’ve dressed my timber to 505mm long, 35 x 25mm section. I have then rebated both sides and ends of the bars, to leave a bar 18mm thick, plus a square ridge along the bottom for the bees to start their comb on. I ran melted beeswax down the ridge, which is advised to help the bees start their combs.
Top bar, with waxed ridge planed into the bottom face (upside down in picture)

Getting bees into the top bar hive

Today’s great event is simply the placement of the open-bottomed top bar box onto one of the family's 10-frame hives. This took some thinking, right up to this morning, and I hope it works.
Bee keeping context is that it is mid-summer, with a good flow of honey from local Orange gums (first Orange gum flowering in about 10 years). I’ve chosen a strong 10-frame "mother hive” which is working hard on honey production.
My first step was to take off a full box of honey from the top of the "mother hive". I can extract this tomorrow with some other boxes.
Then I inverted the order of boxes on the mother hive: I took off the 2 (half filled) honey supers from the brood box, and removed the queen excluder from the brood box. I took the brood box off the base board and put it aside. The 2 honey supers were then placed onto the base board, and the queen excluder placed on top of the honey supers. The brood box was then placed on top of the queen excluder, making a 3-box hive with brood box on top. The open-bottomed top bar box was then put on top of the open-topped brood box, with top bars and a lid on top of the top bar box. There are no openings in the top bar box.
Hopefully the bees are building combs exactly along the bottoms of the top bars
Now the bees have access to the top bar box, to hang combs from the top bars. The queen has access to lay eggs. My plan is that brood and honey combs will be built into the top bar box, and when it’s all looking sweet, I can transfer the combs (on the top bars) into the other top bar box, where the bees will find themselves queenless and rear a strong (but fair) queen and we will have an independent top bar hive to work from.
Once a colony is established with a queen in the nucleus top bar hive, I can build a longer hive (I'm planning on 1200mm) and shift the colony into that, for proper production next year (if I'm lucky).
The main risk (I can see) is that the bees ignore my instructions and build their comb all over the place. I’m hoping weekly visits will be able to push things into line. In hope of encouraging compliance, I have made 3 top bars with central grooves instead of ridges, and attached some strips of foundation wax into the grooves with hot wax. At the last minute I realised that I’ve put in the foundation in the wrong orientation: normal comb has vertical lines in the hexagons, I’ve put the foundation in with horizontal lines. I don’t know if bees will work with wrongly-oriented foundation, let’s call this an experiment…
The other risk is that the queen rearing is unsuccessful, and the top bar hive dwindles on separation. If that happens, I can re-unite it with the 10-frame hive and try again when the season is good.




Thursday, 14 December 2017

Makita electric chainsaw review

Makita UC4041A: a good electric chainsaw for recutting firewood in the shed

Why I bought a new saw

I use electric chainsaws quite a lot, mostly inside the shed, cutting pole wood into firewood blocks. My old Stihl E140 was working fine, but I like to have a backup for the tools I depend on, so I went looking for a new electric chainsaw (see my blog post on electric chainsaws here).

The options

I didn’t see very many options for a good quality electric chainsaw. The Stihl MSE 170 looks like it would be good, but it’s expensive at $380 and I suspect parts are costly too. Stihl has dropped most corded electric chainsaws from its Australian catalogue (they want to sell cordless) and the 170 is the last one standing. In Germany Stihl list 9 corded chainsaws, including a 2.5kw model which runs 3/8” chain on a 16” bar, that costs around $1000. Husqvarna sells a 2kW corded chainsaw in Europe, but not in Australia. Clearly Australia has a weak market for corded electric chainsaws.
There are a few low cost, low quality corded saws available, which I took no interest in. The time spent and the materials wasted on poor quality, un-repairable machines are not worth it. Saws in particular have to work well to work at all.
The Makita was priced at around $200, was available from many retailers, and importantly, had easy and low cost availability of spare parts. Tradetools priced a replacement armature (commonly burnt out) at $62.

The Makita

I like the new Makita chainsaw. It’s sturdy and well made, has good power (for an electric saw), and is comfortable to use.



Makita with Stihl E140: same format really

This is the Makita chain sprocket, which will need replacing every 2 or 3 chains

Bar and chain

In Australia the Makita is only sold with a 16” bar, but in other countries the same body and motor is sold with 12” and 14” bars – much better suited to the motor’s power. In Australia, our timbers are generally harder and tougher than other countries, so a shorter bar makes more sense here, to reduce the load on the motor and provide more power per tooth. I'm not sure why Makita thinks Australians need the long bar, something with Aussie blokes?...
Makita box image appealing to buyers with bar inadequacy issues
A long bar is easily swapped for a short bar, so that wasn’t a deal breaker.
The Makita uses Oregon 3/8” Low Profile chain, which is normal on small chainsaws. The chain and bar supplied were narrow 1.1mm gauge, which cut a narrow kerf (the slot cut into the wood), reducing the load on the motor. The teeth are shorter than standard 3/8LP chain, promising a shorter chain life - they will file away sooner.
Standard Stihl 3/8LP chain above, Makita (actually Oregon) low kickback chain below - note the short teeth and the kickback-reducing ramps in front of the depth gauges
Makita uses the same chain bar base pattern as Husqvarna, so there are plenty of non-genuine 3/8”LP replacement bars available.
The Makita bar above, Husqvarna bar below - same pattern
I was able to buy a couple different 12” bars cheaply online, one of them was described as for 3/8” chain when it was for 3/8” LP. I also buy chain loops from Huztl.net which work very well. Interestingly, different bars sold as 12” were different lengths, needed different numbers of chain links and definitely weren’t 12” long in cutting length.

Cheap bars and chains: some feedback

One of the short bars I bought for the Makita was sold with a “Mondis” branding on ebay, with a chain, for $28 - very cheap. It fit straight on and worked, but needed some attention and understanding to work fully.
Like many cheap Chinese bar and chain sets, the bar groove was significantly too wide for the chain supplied, and the bar rails (the edge where the chain slides along) were not level. I found it worthwhile to hammer and dress the bar before its first use, closing the rails together to fit the chain without sideways slop, and grinding the rail surface square and smooth (see my video on hammering and dressing chain bars here).
The Mondis chain also has some problems of geometry. The cutter top plates are too narrow to cover the full width of the kerf, leaving about 1mm between left and right teeth which isn’t directly cut. This is fine for crosscutting, but means the chain won’t rip because it leaves a wafer of wood uncut down the middle of the teeth. For most firewood cutting, this is no problem, but it does mean this chain can’t be used for ripping.
For someone who just wants a machine that works and pays a shop to do repairs, cheap bars and chains are often a dud: they need some work to be useable, or at least will need some after a short cutting life. However if you are willing to do some saw doctoring, they will do a lot of work and save you some money.

Chain kerf

Trying different chains, I noticed significantly different kerf widths. The Oregon narrow chain supplied with the Makita cuts a kerf of 5.5mm, where the 3/8”LP chain on the Mondis cuts a kerf of 6.8mm: 25% wider than the Makita. Standard Stihl 3/8LP 1.3mm gauge chain (after a few sharpenings - which makes them narrower) cuts a kerf of 6.0mm (10% wider). I’m not sure how much more power the wider kerf takes to cut, presumably more, but I don’t believe it would be 25% more, it certainly doesn’t feel like it is working harder. The main load in normal crosscutting is in cutting the end grain of the fibres, which is the same whatever the kerf width.

Bar and chain adjustment

My preference for simple, durable and repairable, instead of complex and sophisticated, makes me mistrust the tool-free chain and bar adjustment system in the Makita (and plenty of other new consumer chainsaws). My mistrust is comforted, to a large extent, by my assessment that when/if these components break in the Makita, I'll be able to make a relatively simple bush mechanic repair.
Instead of old-fashioned bar nuts, the Makita has a sort of plastic folding wing nut, designed to be undone without using a spanner.
Clutch cover with plastic folding wing nut
This seems robust enough, but if it gave trouble, it is easily replaced with a normal M8 nut, or (more likely for me) a standard Stihl bar nut which has a bigger bearing surface and can be turned with a normal chainsaw tool (and is available very cheaply from Huztl.net).
See: a Stihl standard bar nut spins straight on. That feels better. 
More potentially problematic is the chain tensioning mechanism, with a finger wheel, presumably using a pair of bevel gears to drive the chain tensioning thread. This works fine but feels flimsy. If it broke, it looks like it could be easily enough removed and bypassed by drilling through the plastic housing beside the bar, to install a traditional bar-side chain tensioning screw (oh for simple, reliable, old-style machines...).
The black metal bit below pushes the bar forward to tension the chain. I reckon it could easily be replaced with a traditional bar-side screw by drilling thru the plastic 
This vulnerable-looking chain adjustment mechanism is probably the aspect of this saw I feel most sceptical about. However I see it as easily repairable, and thus something I can easily live with.

Safety

The Makita has all the usual safety features of good electric chainsaws. It has a thumb button which must be depressed to use the main switch (I want to call it the throttle, but it isn’t). It has an effective chain brake for kickback. It has a run-down brake which stops the motor quickly when you take your finger off the main switch.
The chain supplied by Makita is low-kickback chain, which has a geometry that reduces the digging-in of teeth when they’re going around the bar nose. The disadvantage of this type of chain is that it also makes the chain poor at boring cuts, where you do want the chain to cut as it turns around the bar nose. I prefer to use standard chain and be able to do boring cuts, but for the infrequent chainsaw user, the low-kickback chain is safer.

Summary

The Makita works very well. 1800 watts of power is noticeably more than my 1400w Stihl, and makes it easy to maintain high motor rpm (this is very important to avoid overheating the motor - see my post on electric chainsaws). It seems robust and well built, and after a few hours of use I’m very happy with it. I’m careful not to do frequent starts (which heat the motor) when cutting small pieces: I take the risk of keeping the motor running between multiple cuts. I would advise avoiding cutting with the full bar length, and considering a shorter bar and chain. Overall, this seems to me like the best buy for an electric chainsaw in Australia.

Sunday, 3 December 2017

Getting the most from electric chainsaws


Here I explore some of the issues for electric and low-powered chainsaws, including the sensitive question of bar length

The benefits of electric chainsaws

We have a shed full of petrol chainsaws, which are a marvellous technology: powerful, fast, reliable and able to work anywhere. No other household technology can deliver such a big energy return on energy invested: delivering large amounts of wood fuel energy from a small amount of fossil fuel.
Compared to petrol saws, electric chainsaws are much less powerful and much slower for bigger cuts. They are also more fragile: their motors can be quickly wrecked by labouring them. But if you treat them right, electric chainsaws are an economical and helpful asset for the frugal household. They are cheap to buy and run, and last a long time if used carefully. They start instantly and easily – a boon to the house without bush mechanic skills. In our household electric chainsaws use free surplus solar electricity from our PV panels (we only use them when it’s sunny) to produce wood energy. They make no smoke and can be used comfortably in a shed. They are relatively quiet and don’t fill our valley with motor noise. They require much less time on maintenance – the motors go for years needing only cleaning with compressed air. When used for the right jobs, with care and understanding, they’re great.

Cordless electric chainsaws

A Stihl cordless electric chainsaw: I wouldn't have one
Battery-powered chainsaws are becoming prominent in the shops, but they look like a poor deal to me unless you’re doing a lot of something that really uses their cordless characteristics (perhaps like pruning trees in an old people’s home). Lithium batteries are remarkable energy carriers, but they are very expensive, use a lot of energy and valuable materials to produce, and they only last a few years. I love lithium batteries for electric bikes, where their power is a good match for the job, and they help to take a whole car off the road. But I think cordless chainsaws are pushing the battery thing past its effective zone: only just enough power for a very small chainsaw, a short charge life, requiring frequent recharging or multiple batteries, expensive saws and expensive batteries, and expensive replacement in a few years. 
I service a family cordless chainsaw (a Stihl), and I'm very unimpressed: the chains are extra narrow to reduce cutting load, but have tiny teeth with a very short life. The bars are also small, light, weak and short-lived. Over time, the cost (money and resources) of the saw, plus batteries, plus chains, bars and sprockets, promises to be far more than a larger saw. Really, the only plus is that they're quiet and don't need an extension cord. 
If your goal is frugality and energy efficiency and your product is household firewood, I'd leave cordless chainsaws alone. I expect far less cost and fossil fuel will be invested in using a petrol saw to cut wood into lengths in the forest, then recut back at the shed with a corded electric saw, than the embodied manufacturing energy in a cordless saw and batteries.

My experience with electric chainsaws

I’ve had good and bad experience with electric chainsaws, over 20+ years. My first was a Stihl E20, a marvellous 2kW machine made for professional use, comfortably pulling 3/8” chain on a 16” bar. It did a lot of work before its armature was cooked while a friend was using it. I was unable to get a replacement armature at the time, so it went into a sack in the shed. I was recently quoted $355 for an armature: this seems excessive to me so I don’t plan to repair it currently. Stihl no longer sells the bigger electric saws in Australia.
I then bought a Stihl E140 (1400W), which has worked well for over 10 years and cut many tons of wood. It’s mostly used in the shed for firewood: re-cutting short poles of smaller diameter wood to stove length. It cuts clean wood, up on a saw horse, so chains stay sharp for surprisingly long and have long lives.
Here's my Stihl E140, on the saw horse where it's cut many tons of wood
I’m very careful to maintain a high motor speed while using this saw, being conscious of the many power tools I’ve seen that have had their motors burnt by being worked too hard and run too slow.
My E140 was supplied with a 14” bar running 3/8 low profile (LP) x 1.3mm gauge chain. This has always been obviously too much bar for the saw: the motor can’t pull that many teeth through wood without being overloaded.
I now have a Makita 1800w electric chainsaw, reviewed in the next post. It's good, cheap and repairable at reasonable cost - I think Stihl has lost me as an electric saw customer. 
Makita and Stihl E140 side-by-side: basically the same layout

Who’s got the biggest bar?

To get the most from small saws, especially electric, we do need to talk about bar length.
Marketing of domestic chainsaws seems to focus on exploiting blokes’ macho anxieties, and I reckon most small chainsaws are sold with bars that are simply too long for them. It’s as if people are being told they’re getting more saw if the bar is long – but they’re not.
Box photo designed to plug in to bar-length anxiety disorder
With all chainsaws, you get the best out of them with the shortest bar that will do the job, and this is much more so with low powered saws like electric ones. Short bars are safer: their noses are less likely to contact another piece of wood behind the cut and cause kickback, if they do kickback they have less leverage over the operator’s arms, and they are simply safer by being more compact. Short bars make a saw lighter to carry, quicker to sharpen, and lubricate bar and chain better with a given amount of oil.
On top of all this, a short bar makes your saw more powerful (in effect). There’s less chain dragging through less bar groove and wasting power on friction. Most importantly, a short bar sets a maximum number of teeth that can cut wood at the same time, which has real advantages.
With all types of saw, a key issue is power per tooth. When a saw is cutting, the motor power must be divided amongst the teeth that are actually cutting wood. The closer together the teeth are, the more teeth bite at once in a given cut, and the less power each tooth can have.
Up to a point, the more power each tooth gets, the more efficient the whole sawing process is: the tooth can cut deeper, lift chips instead of dust, and the tooth will stay sharp longer because it isn’t "rubbing" (rubbing is when a saw tooth rubs dust off the surface instead of biting under and lifting chips or a shaving. It happens to any type of wood saw if it's too blunt or underpowered).
A tooth that is biting deeply and cutting good chips will produce a high volume of chips, that are more likely to fill the space between the saw teeth, potentially overloading the cut with sawdust. Wider tooth spaces and shorter cuts can remedy this.
Lots of low-powered saws are sold with 16” bars (including the Makita reviewed in my next post). This is (I find in practice) too long for them. These saws don’t have enough power to pull 16” of teeth cutting at full depth, and if you try, their motors will overload and bog down, risking motor damage. To avoid overload, the operator can hold the saw back and make the teeth rub, which is slow and inefficient and also blunts the saw. He (or she) may rock the saw so that fewer teeth are cutting at any one time – clumsy and ineffective. If the operator pulls the saw back and uses the outer half of the bar, it will reduce the number of teeth cutting. However this seriously risks kickback, as the spikes are not engaged in the wood and the tip of the bar is pushed into the back of the cut, with a lot of leverage over the operator’s arms. These issues of power and safety are easily addressed by using shorter bars.
If you really need a long bar on a low-powered saw because you can’t do your cut any other way, you can increase the power per tooth by reducing the number of teeth along the chain. One way to do this is using “skip tooth” chain, which has 2 (or sometimes 3) blank links between teeth, instead of the usual 1. This is often done in chainsaw milling, where long bars are often used cutting in a difficult orientation (teeth ripping across end grain). Another option, also used in chainsaw milling, is to take a normal chain and grind away most of the top plates of a proportion of the teeth, following the style of Granberg ripping chain (have a google) - this doesn't have to be just for milling. 
Photo of modified chain
If you’re using a long bar so you can cut wood on the ground while standing up, there are often better ways. Squatting and kneeling are both good for your body! And you will reduce your cutting into the ground – the reliable way to blunt your saw and wear your bar.

Getting a shorter bar

My advice (if it isn’t already obvious) is to use a short bar on an electric chainsaw: 12” is a good size for most. You may be able to ask for a short bar on purchase, but most saws come in a box without options, so you may need to change bar and chain yourself.
If you want to buy a bar for a saw, you need to first know the chain pitch: this is a measure of how big the teeth and links are. Most consumer electric saws have a pitch of 3/8” Low Profile (also called 3/8LP or 3/8P). 3/8” means that the average length of a link in the chain is 3/8 of an inch (measure the distance between one rivet and the second one on, and halve it). A saw with a pitch of 3/8” LP will have a drive sprocket (on the motor) of 3/8” LP, and the bar will also have a nose sprocket of 3/8” LP.
3/8” Low Profile is different from and not compatible with standard 3/8” saw chain. It is specially made for small saws. Stihl calls it “picco” chain. 3/8LP has largely superceded the old ¼” chain for small saws, because it has 1/3 fewer teeth. In line with the principle explained above: on a lower powered saw, you want fewer teeth so that they each have more power. I’ve noticed that 3/8” LP bars are often sold as 3/8” (without mention of low profile), which is not helpful. This can make buying online a bit risky, but I’ve never heard of a 12” 3/8” not-low-profile bar, so that helps.
The chainsaw bar and chain have another critical measure: the pitch. This is a measure of the thickness of the chain drive links: the hook-triangle shaped bits that run in the groove. If the sprocket on the chainsaw is 3/8” LP it can drive any gauge of 3/8” LP chain. However the bar and chain need to be the same gauge, or the chain will be too tight or too loose side-to-side. If you are getting a new bar for your chainsaw, you don’t need to use the same gauge as your old bar, but you need to ensure you get chains of the same gauge as the new bar.
Chain of a particular pitch and gauge can be bought either in ready-made loops, measured by the number of drive links, or you can buy a roll (usually 25 or 100 feet long) and make your own chains. Riveting chain into loops is relatively easy, and doesn’t need any bought tools if you have a little metalworking ability.
Cheap Chinese bars are okay, if you are willing to give them some attention before using them. The ones I’ve been trying on my electric saws seem to mostly be made for pole saws: 12” bars, taking 3/8” LP 1.3mm gauge chains. A number of these I’ve tried seem to have too wide a gauge of bar groove for the chains supplied with them (like some Baumr chainsaws – see my review here). This will probably work fine when new, but will become a problem after a while. Hammering a new bar to fit the chain gauge is a reasonable solution, which I’ve used sometimes. Cheap bars sometimes also need dressing: filing, grinding or linishing the bar rails (the surface the chain runs on around the edge) to make them square. Here's a video on how to hammer and dress an old bar:

Electric motors

A key thing about electric chainsaws is that they have electric motors (!), and that these are very different from petrol motors. What kills petrol chainsaw motors is (roughly speaking) going too fast or too dry (too little oil or too lean a fuel mixture). What kills electric motors is going too slow.
The faster an electric motor goes, the less power it draws. The slower it goes, the more current it draws and the more heat it generates in the motor.
When you first switch on an electric motor, it draws a huge current for a short time until it spins up. Next (before it gets a job to do) it uses minimum current when spinning at top speed with no load. Then, as the motor is loaded up and slows down, it draws more current and becomes more powerful. However if the motor is further loaded and slowed even more, the current increases but the output power decreases. When it’s bogged down, a high proportion of the electric energy stays in the motor as heat (instead of leaving as shaft power), and the copper windings heat up. If the copper windings get hot enough, their insulation will start to fail, and electricity can then find short circuit paths through the motor, making even more heat and “burning the motor out”. 
Brush motors, as used in mains powered chainsaws, drills, circular saws etc., often show this sort of winding failure as arcing around the brushes. This is usually a symptom of winding failure in the armature: the spinning rotor in the centre of the motor. Burnt armatures can’t generally be repaired, but they can often be replaced if reasonably priced. I recommend checking the price of a replacement armature when considering a new electric chainsaw (or other large brush-motor power tool).
Some electric chainsaws, including my Stihl E140, are made with a thermal cutout switch, to help protect the motor. This switch doesn’t sense the temperature of the motor windings, instead it is designed to heat internally in a similar way to the motor, and to switch off when the current has been high enough for long enough.

Electric chainsaw consumables

If you’re using an electric chainsaw to produce firewood, or some other repeating task (not just pruning the garden twice a year), it’s worth being conscious of what parts you can expect to consume over time.
Chains and sprockets are the main consumables of any chainsaw. These parts wear and are replaced together, like the chain and sprockets of a bicycle.
It’s most economical to rotate 2 or 3 chains together with one sprocket, then replace chains and sprocket when the chains are sharpened away. As most chainsaws are sold with a single chain and a new sprocket, it’s good to decide on what bar you intend to use soon after you get your saw, and get 2 or 3 chains to suit. This could be from the seller, or from another supplier, especially if you are chainging bars. I change chains and turn over my bar (to wear both edges evenly) every few sharpenings, swapping to the chain with the longest teeth.
I usually use chains until teeth start breaking off, because the teeth have been sharpened so far back. By the time they are this worn, they cut a narrower kerf and are more difficult to use.
The sprocket will take a long time to wear – you’ll have to wear out 2 or 3 chains first. However I like to have these things in stock well ahead of time: living out of town it saves a lot of cost and trouble to be well stocked.
The bar will last for a few sprockets – which is years of cutting. Unless they get bent by a big log falling on them, well maintained bars wear out by the groove becoming too shallow for the chain – so the drive links reach the bottom.
Electric chainsaws, used with care, will eventually wear out their motor brushes: the carbon blocks that conduct electricity into the spinning armature. Some brushes are made so that they stop working before they wear down to their springs and damage the commutator on the armature (the ring of copper bars on the rotor). Sometimes a power tool suddenly stops working, appears to be dead, but simply needs a pair of new brushes worth a few dollars.

Summary

Electric chainsaws can be a useful and economical part of a firewood cutting system. If you want a long and productive life from your electric chainsaw, keep them spinning fast and running cool and avoid frequent starts. As a key to working your saw within its capabilities, I recommend looking sceptically at the supplied bar length and considering how you can give the fragile electric motor an easy life with a short bar. Running 2 or 3 chains in rotation will reduce maintenance costs.