Shortening a chainsaw bar

Shortening chainsaw bars has worked very well for me - most of my chainsawing is done with saws using bars I've shortened. This post outlines the reasons for shortening a chainsaw bar, and explains how to do it.
This is a revised (June 2020) version of an old post, incorporating what I've learnt over the past couple of years. Some of my other posts relevant to this one are:

Holzfforma chainsaw bar review

Baumr SX45 (Chinese 4500 45cc chainsaw) Review

Huztl Farmertec 036 MS360 chainsaw kit review

Holzfforma/Huztl Alaskan Chainsaw Mill Review (with Huztl MS660)

Shortened bar on a Huztl 036 kit saw

Why shorten a chainsaw bar?

I like my chainsaws to have bars as short as practical. This has many advantages: a lighter unit to lift, gives the motor an easier life, less bar and chain to lubricate, more power for the teeth in the cut, quicker sharpening, cheaper, etc.. A short bar is easier and safer to use when thinning thick re-growth, as I spend a lot of time doing. Overall, a chainsaw is more powerful and easier to use, when it has a short bar.
Despite this, chainsaws tend to be sold with way oversized bars. This is a modern fashion. For example, the 036, Stihl’s 60cc professional saw in the early 1990s, had recommended bar lengths of 37cm (15”) and 40cm (16”) and I think they were right. The current Stihl catalogue shows the current version of this saw, the MS362, fitted with a 50cm (20”) bar as standard. In Australian hardwoods, that's a toddler wearing daddy's boots...
Short bars are hard to get, unless you want to pay full price for a genuine Stihl bar (which is an option worth considering). Cheap chainsaws come with way-too-long bars, and cheap bars tend to come in long sizes. If you have a few chainsaws hanging around, you’ll probably have too many long bars and too few short - I do. That’s what made me want to try shortening bars.

How long a bar should I use?

Here’s what I reckon about suitable bar lengths for chainsaws in the woods I cut (a range of Australian woods, mostly hardwoods). It mostly depends on engine power, which depends on engine size in cubic centimetres (cc).

30cc - 40cc

I recommend 30cm (12”) - that’s what I use on electric saws and Stihl MS 170 and MS180. Saws this size usually use 3/8” low profile (often shortened to 3/8LP or 3/8P) chain. This is the smallest type of chain these days. 3/8LP has the same number of teeth per length as 3/8” chain, but the teeth and links are smaller.
3/8LP bars and chains on new saws are often 1.1mm gauge (the thickness of the drive links that go into the bar groove), which is very thin and has very small teeth. This reduces the load on the engine, but the teeth are tiny and sharpen away quickly. I usually use the thicker 1.3mm gauge bars and chains, which are more robust and last longer.
A 12” bar ideally uses a chain with 44 drive links (44DL) - a multiple of 4 is best. However some (including the Hurricane brand 3/8LP 12” bars) come with a 44DL chain, but after the chain has stretched it needs to be shortened to 43DL or you can’t tension the chain - the bar is a little too short. That’s bad design.

40cc - 50cc

I recommend 33cm (13”). This is what I use on all my Stihl 024 (42cc) and Baumr SX45 (45cc) saws. Saws this size usually use .325” pitch chain. Husqvarna uses 1.5mm gauge and Stihl uses 1.6mm gauge - but the engine part of the saw doesn’t care what gauge the chain is. 1.6mm gauge is easier to use if you’re shortening a bar, because you can get 1.6mm thick cutting discs for your angle grinder. If you’re cutting down an old 1.5mm gauge bar, it probably is worn enough to take 1.6mm gauge chain. If you’re cutting down a new 1.5mm gauge bar, check if a 1.6mm gauge chain will fit: most Chinese and some GB bars marked as 1.5mm are wide enough to take a 1.6mm chain no worries.
A 13” long, .325" pitch bar normally takes a 56DL chain. 

Here's a 45cc Chinese chainsaw with a 13" bar, with 56DL .325" chain. Just right.

60cc

I recommend 40cm (16”). Saws this size use 3/8” pitch chain. Stihl 036 or MS360 is a good medium-sized saw for cutting medium-sized logs into firewood or cutting up bigger tree heads. With an 18” or 20” bar it struggles to pull the chain through hardwood, but with a 16” bar it’s in the zone.
The first bar I tried cutting short was an 18” Holzfforma bar (the shortest they sell), that I cut down to 15” for my MS360 Huztl kit saw. 15” (56DL) is really nice on an MS360.
A 16”, 3/8”pitch bar should take a chain with 60DL

70cc

I recommend up to 50cm (20”). Saws this size use 3/8” pitch chain. I use Stihl 038s a lot (the new version is the Stihl MS381), that have 72cc motors and are fine with bars up to 20”. A 16” bar is great on an 038 for cutting hardwood - not only shorter but noticeably lighter, and you start to feel the weight of this size of saw.
A 20” bar should take a 72DL chain.

90cc

20” to 29” is good. These saws usually use 3/8” pitch chain. If you’re cutting timber that needs longer bars than that, you probably need a bigger saw with .404” pitch chain. I usually keep 28” and 29” bars with 3/8” chains on my Huztl MS660 kit saws, mostly for freehand ripping and Alaskan milling. A saw that heavy with that long a bar is hard work to carry around, so you’ll probably only use it for big cuts.

What bars do I cut short? Cheap, old or small

Most of the bars I shorten are cheap Chinese bars. Lately I’ve cut down a few on Chinese 45cc/4500 chainsaws (like the Baumr SX45 I review in this post) that are usually sold with 18” bars but do very well with 13”. I cut the 18” bars short, put on a 1.6mm gauge chain (the bars are way over-gauge for the 1.5mm gauge chains they come with) and they work very well.
The cheap bars from Huztl/Farmertec don’t come in short lengths, so I’ve cut down a few of them too. To make a 13” x .325” pitch x 1.6mm gauge bar, I buy the 16” x .325” x 1.5mm gauge bars for Husqvarna, cut them short and use 1.6mm gauge chain (all Chinese bars seem to be way over-gauge). To make a 16” x 3/8” x 1.6mm bar, I reckon a 20” x 3/8” x 1.5mm bar for Husqvarna would be a good start. Remember these aren’t great quality steel, so you’d do this because you couldn’t afford a good quality bar or you didn’t plan to do a lot of work with it.
I’m reluctant to cut down a genuine Stihl bar, unless it’s badly worn at the base - this often happens when lots of firewood is cut with a blunt chain: the saw is pushed down hard, the wood close to the engine for more effective pushing.
I have occasionally cut genuine Stihl bars I thought I’d never use, like 16” .325” pitch bars.

Horsepower per tooth

There’s an important way to think about saws: horsepower per tooth.
If a saw tooth has enough horsepower, it can bite into the wood and peel off a reasonably thick chip of wood. If it doesn’t have enough power, biting in can overload or stall the motor driving it, so an underpowered saw tooth tends to rub on the surface and scratch off a fine dust, because the person using it will tend to hold the saw back. Chopping wood into fine dust takes more energy than making chips, thus wasting what little power is available and bluntening the tooth much more quickly. Up to a point, taking a deeper cut and making a thicker chip uses the saw’s power more efficiently.
Too much horsepower per tooth risks breaking the tooth or the chain, or loading too much sawdust into the kerf (saw cut), but this is a rare problem in chainsaws.
You get more horsepower per tooth with a bigger motor, and less with more teeth in the cut. So a saw with a small engine and a long bar, cutting a wide piece of wood, has not much horsepower per tooth. The motor will tend to be overloaded, so the operator tends to rock the saw up and down to keep fewer teeth cutting, and/or hold the saw back so the teeth dig in less. The sawdust will tend to be fine, the teeth will blunt more quickly, and it won’t be much fun.

Depth gauges

You can limit the power each chainsaw tooth uses with the depth gauges - the little ramped pegs in front of each tooth. The shorter the depth gauge is, relative to the top of the tooth, the deeper the tooth can bite in. If the depth gauges are too high (and the teeth are sharp), the teeth can’t get enough bite into the wood and you can’t load the engine up with work - quite like having blunt teeth. If the depth gauges are too low (and the chain is sharp), the motor will be overloaded - sometimes I’ve wondered if I have an engine problem, but I’ve just had too low depth gauges (common with new Chinese chains).
As chainsaw teeth are sharpened, they get shorter and lose height. This reduces the difference in height between the teeth and their depth gauges, so reduces the depth of cut. To maintain the amount of bite of the teeth, the depth gauges need to be filed down a little from time to time.
Manufacturers recommend trimming the depth gauges with a special file guide to a standard height. However you can adjust the heights to suit the saw and chain. A 72cc Stihl 038 with a 16” bar can pull a chain with lower depth gauges (a greater depth of cut) than a smaller saw with the same type of bar and chain, and cut better. A small saw carrying a long bar needs higher depth gauges, so each tooth doesn’t need so much horsepower. I tend to adjust my depth gauges on feel: if the chain is freshly and properly sharpened and the bar is in good condition, does the chain pull the bar into the wood and load up the motor just right? If not, maybe the depth gauges need a trim. But be careful - a chain with too-low depth gauges overloads the motor and is hard to use. Don’t get tricked into trimming the depth gauges when you have a blunt chain.

Skip tooth chains

You can get more horsepower per tooth if the teeth on your chain are further apart, meaning you have fewer teeth cutting at one time. You can buy “Skip tooth” chain, made with more links between the teeth, so they have fewer teeth. You can also modify chains by fully or partly removing some of the teeth, like “Granberg ripping chains”.
If you really need to use a long bar on a small motor, skip tooth chain, modified chain and high depth gauges are all useful tricks to avoid overloading the motor.

How to shorten a chainsaw bar

What tools do you need?

The main tool is an angle grinder with cutting discs: this machine  is what makes shortening bars possible in the home workshop.
I recommend buying a box of 1.6mm thick discs (normal cutting discs are 1mm these days) - these are great for cutting the chain groove. I get them from Smith and Arrow, and I’ve been happy with them. Take care: I’ve found that when they’re brand new, cutting discs tend to have a bit of surplus grit around the perimeter, which can cause them to cut a groove wider than 1.6mm. Make sure you do some lower accuracy cutting with a new disc to wear the perimeter down to size, before cutting a chain groove.
A drill press is really good for drilling the holes in the bar. It could be done with a hand-held drill if necessary, but you’re more likely to break your drill bits. If you don’t know how to sharpen drill bits, this is a good time to learn, as bits get blunt a lot when drilling high carbon steel (like chainsaw bars), especially when you run into the spot welds.
A bench grinder is good for grinding the outside profile of the bar, after cutting with the angle grinder.
A flat file will help clean the bar stud slot after drilling and cutting.
A linisher is good for finishing the bar rails, but you could do this with a bench grinder and a file.

Decide on the finished length

It’s good to get the bar length right so that the drive link count is a multiple of 4, that way you have evenly spaced left and right teeth all the way around. It also makes it easier to make loops from a roll of chain because you only need to cut each length once.

No bar to copy?

If you don’t have a bar to copy, start by making a chain the length you want. Here’s some photos from me cutting down a cheap Holzfforma bar to fit a chain with 56 drive links.

I looked at a 60 link chain on a 16” bar and rim sprocket:

Measuring the gap on a 16" bar

The 56 link chain trying the bar for size

I used a genuine Stihl bar to mark out the pattern of slot and holes on the Holzfforma bar.

Using the Stihl bar to mark the slot and holes

Then I punched and drilled the bar.

Drilling the holes

cutting the slot with angle grinder with cutting disc, using a steel bar as guide

I did have an interesting challenge in this process. When centre punching one of the bar tensioner holes, there was a small bang, and I found myself with a splinter of steel surprisingly deep in my pinky finger, a punch with a flattened point and no mark left on the bar. By chance the tensioner holes aligned with spot welds from laminating the bar layers, which had left hardened patches of steel (spot welding brings spots of steel to melting temperature, and when the electrical resistance heat is suddenly stopped, the heated spots are quenched by the cold steel around, which will cause hardening in carbon steels). I first tried to deal with this by moving the hole a little, but ended up having to temper the steel with heat to make it drillable. Thus the tensioner holes are a little misaligned.

The bottom hole is right on the hard spot weld - see the failed punch mark

Cutting the slot between the holes

Filing the slot after grinding

Chamfering the hole edges

Chamfering the hole ends

Cutting the bar to length - there's no turning back now!

cutting off the corners

Grinding a curve onto the bar

Smoothing the bar shape on a linisher

Grinding the bar slot into the bar base with a 1mm cutting disc

Tempering the bar with LPG-air torch to enable drilling

Drilling the bar after tempering

Drilling the oil holes using the old bar base as template

The new bar fitted to the motor

Shortened bars can look a little wider than normal at the base, but I can live with that

Bar hammering video (for worn or badly gauged bars)

Shortening a .325" bar

Here's some phtos of shorteneing .325" pitch bars for a Stihl 024 (my post on repairing 024s and 026s here).

Here's the genuine Stihl 13" bar alongside the Holzfforma 16" bar

I traced directly from the Stihl bar, but the new bar will need to have an open-backed slot because of the existing slot

Here's the freshly repaired 024 with the freshly shortened .325" bar 

Both chain tensioner holes ran into hard steel from the spot welding: the burnt-looking areas around the holes are where I softened the steel with an oxy flame

Shortened bars work well

My friends and I have now done many hours of cutting on many saws with bars I've shortened. We’ve had no problem at all with the hand-modified bars (tho I've had serious quality problems with the Holzfforma bars). This is a technique that works well and is very useful. 

Bar lengths

As I said above, I often start off by copying an existing  bar. Watch out for this, sometimes bought bars are shorter than ideal, meaning that you may need to shorten chains as they stretch beyond the limits of the chain tensioner.

 

13" bar, 56DL, .325" pitch (used on my Chinese 45cc chainsaws): 395mm bar length (this is 10mm longer than the GB bars).