Working Edges: Part Two.

In the last post we looked mainly at how cutting angles affected the working edge and how not using the file with an even stroke causes the working edge to become rounded. In this post, we'll compare the working edge of a semi-chisel cutter and a chisel cutter - and look at one of the most common faults when sharpening the semi-chisel version. Find out more after the jump...

We of course know that the working edge should be kept at the correct angle and that the edge itself should be straight. This is pretty easy to see when maintaining a chain with chisel cutter as the top plate very definitely meets up with the side plate. After all, it's this that gives the chisel cutter its characteristics - the working corner that comes to a well-defined point that allows the wood fibres to be severed.

However, the semi-chisel cutter does not have this same defined point as there is a curved surface between the top and side plate. This affects the working edge as it no longer stretches the entire width of the cutter, in fact, it almost looks as if the corner has been knocked off or made blunt! The main thing here when sharpening is to ensure that there is a straight edge running from one side to the other side of the top plate - and this is where I see many people who are just learning to sharpen get it wrong. They tend to stop filing slightly too early, achieving a straight edge which, unfortunately, does not go right across the leading edge of the top plate; placing a straight edge against it shows up the problem. The solution? On most occasions it takes just one or two more strokes of the file to sort it out.

I tend to use the straight edge of a file guide to check this leading edge, it just acts as confirmation, but you should be able to see it fairly clearly in good light. You'll see where the curve starts as it leads from the top plate round to the side plate - there'll be a difference in the way the light hits the cutter and it shows exactly where the edge of the top plate is. Follow this line forward to the working edge and make sure that it's straight from this point to the other corner of the top plate - hopefully the picture shows this better than I can explain it.

Cutter Lengths.

Continuing our look at common problems encountered when sharpening the chain, in this post we'll take a look at the effects of variable cutter lengths.

When you first start sharpening your chain, it's natural to wonder where to start, i.e. which cutter do you choose to begin the process? Does it even matter? Well, yes it does! Find out more after the jump.

Many of those coming to the chainsaw maintenance and cross-cutting courses don't realise that it's important to start filing the correct cutter when sharpening as you must end up with all the cutters filed to the same angle and the same length. And the clue is in those last few words - they should all be the same length.

This means that you have to base the length of all the cutters on the shortest cutter; but why does it matter? Surely as long as the filing angles are correct, the length of the cutters is irrelevant? Errr, no.

The main problem with having the lengths all different is that it will cause the chainsaw to cut in a curve rather than a straight line. There is a very noticeable drift from the cutting line, and I've seen it referred to as a 'banana cut' on the ArbTalk forum just recently. This is a good description!

So, when we start to sharpen we must find the shortest cutter - but what if there's a longer cutter that has lots of damage? What if they're all the same length? What if you don't have a set of vernier calipers to hand to check? Let's deal with each of these in turn...

Damaged Cutters

In theory, as long as you only cut wood with your chain the cutters shouldn't get damaged. But life being what it is, sooner or later you'll cut through some timber only to see sparks coming out of it - then there's the sinking feeling that you've just found a nail, or part of a wire fence, in the middle of the wood. Maybe you touched the chain on the ground as you exited a cut, or maybe there was just lots of small bits of flint in the rough bark of an old Birch tree. Whatever it is, one day you'll end up with the leading edge (or working edge) of the cutter getting damaged.

The main thing is to file away all the signs of damage. Now in our example where there is a longer cutter which is damaged, it makes more sense to file this first of all and then check it's length against the [previously] shorter one. If it's still longer, then it'll need to be filed more; if it's now the shortest one, then this is the one you'll base the rest on.

Same Length

If all the cutters are the same length, and none are more damaged than any others, then you've got no worries - start anywhere!

No Vernier Gauges

For the utmost accuracy you can use vernier calipers - but there really is no need, unless you pride yourself on engineering tolerances that NASA would be proud of. Use the simple nut and bolt trick - one bolt, fitted with two nuts is all you need. Fit the head of the bolt between the working edge and loosely tighten the first nut up against the trailing edge of the cutter (use the second one to lock it in place). For more information, check out this post...The Nuts And Bolts Of Meaasuring.

Setting The Lengths

Once you have sorted out any damaged cutters, and you know which one is the shortest, make sure that it's sharpened correctly and then measure along where the side plate and top plate meet. Set your measuring apparatus to the required length and don't forget to mark it!!. I just use a permanent marker to colour in the top plate so I know when I've gone round the whole chain.

Try to get the cutters all the same - if you don't you'll find it more difficult to get accurate felling cuts, particularly when using the medium fell technique as the saw will drift of course as you cut around the back of the tree. You might also find that you suffer from more vibration when you use the chainsaw, as the chain reacts to the odd lengths.

In the next post we'll take a look at filing angles and the working edge.

Left Hook

There's a lot of criticism within the industry surrounding the ability of chainsaw operators to correctly sharpen their chains. It's not helped by those in the industry who persist in setting out the same old myths that have been around for years. If you want the best performance from your chain then it needs to sharpened correctly.

Incorrect sharpening of the chain can lead to varied problems, from slow cutting performance to a greatly increased chance of kickback. Knowing how your chain should be maintained is extremely important - yes, it's a drudge but it needs to be done.

Here on DriveLink, sharpening the chain was covered in the following posts:

1. Chain sharpening: part one.


2. Chain sharpening: part two.


3. Chain sharpening: part three.

So, let's try and take a closer look at some of the problems encountered when sharpening. Find out more after the jump...

First off, it's important then when using the file that we keep it flat and straight whilst filing. We also need to maintain the correct pressure to ensure that the correct side plate angle is maintained. Now, it's difficult to measure the side plate angle correctly, although Stihl have attempted to make things a little easier with the various markings on their depth gauge tool; instead, when I teach sharpening I tell the students to use the angle specified in the manufacturers literature as a guide to how much 'hook' their should be on the side plate. An angle of 85^o would suggest little hook, whereas an angle of 60^o would show a definite hook in the side plate of the cutter.

The picture here shows a chain where this hook is completely wrong - the cutter actually appears to lean backwards and there's no hook at all. There's two major reasons for this:

• the file used to sharpen the chain was too large;


• too little pressure on the file whilst sharpening caused the file to ride up.

If you suspect the file you used was too large, check it against the filing table for your particular chain. If you use Oregon chain, check out their maintenance and safety manual at the manual - it's full of really useful information.

But what if you used the correct file size? It's likely that the lack of hook on the cutter was due to the file riding up as you sharpened - you'll be able to see this if you look at the shape of the gullet (between the cutter and depth gauge). If there's a ridge starting to form then it's a sign that you should have used a little more pressure - get rid of this ridge before you continue sharpening.

There is another possibility, and that is that you did not hold the file correctly - if you used a file guide, it should rest on the cutter and the depth gauge.

Try to maintain an even pressure on the file - not too much and not too little. Too much pressure results in the opposite problem; i.e. too much hook as the side plate is being filed by a different part of the file, resulting in what is sometimes referred to as a 'birds-mouth'.

Next post we'll take a look at cutter lengths.

Chain Sharpening (Part 3)...

Continuing on our journey to achieving a sharp, effective chain, in this post we'll look at the depth gauges and find out one way of setting them. More after the jump...

The depth gauge at the front of the cutter fulfils an important function - to regulate how much timber is actually cut. For this reason, it's important to keep these set at the correct height relative to the cutting edge - left too high and you'll not get an efficient cut, too low and you'll try taking too much wood out in one pass.

Leaving the cutter too high will occur if you don't check and set it regularly - as you sharpen the cutting edge, the height of that edge is actually reducing, and that means that you'll not be cutting as much as you could do. So, with the depth gauge left too high, by not setting it...

• Inefficient cutting as you could be cutting deeper.


• Takes longer to carry out the task.

But that's just mildly irritating when compared to the potential disaster that could await you if you decide to file the depth gauges down to much, and therefore try to cut too much timber in one go. So, for filing the depth gauges too low...

• ...you'll be trying to cut too much wood.


• ...vibration from the chainsaw increases dramatically.


• ...the saw may appear to be less powerful as it tries to keep up with the cut.


• But, worst of all, you massively increase the chance of kickback.

The tolerances for the depth gauge are fairly small, and 25 thou (0.65mm) is not uncommon. To maintain this setting there are a number of devices available on the market, from Stihl, Husqvarna and Oregon et al.

We'll take a look at some of these later on, but for now we'll use the simplest Depth Gauge Tool.

This tool, shown in the picture, can be laid on top of the chain with the notch at one end allowing the depth gauge to poke up through. You will need to remember two things if it needs to be filed down:

1. You must only file depth gauges on the other side of the bar to you.


2. You shouldn't file the depth gauge with the tool in place, otherwise you will effectively be altering the measurements set by using this tool.

Whilst you might be able to see the depth gauge poking up through the tool, it's easier to use a straight edge to run over the notched end of the tool. If the depth gauge is too high then it will catch on your straight edge.

If your depth gauge tool is like the one shown in these images, you should leave the tool in place whilst you file... but lift the back end up first. This has two advantages: 1) it uncovers the depth gauge giving you access to file it, and 2) it protects the cutting edge that you just sharpened.

That's about it really, work around one side, checking and setting as appropriate before turning the saw around and doing the other side.

Chain Sharpening (Part 2)...

Back in part one of chain sharpening, we took a look at the filing tables to ascertain the file sizes and angles that we'd need to use to maintain our chain properly.

After the jump we'll take a look at how we should decide where to start filing.

Deciding Where To Start

How would you choose which cutter to start filing? When I pose this question whilst teaching, one common answer is along the lines of "whichever one is on top".

But it's not quite that simple (you knew it wouldn't be didn't you?). So, how do we go about selecting the first cutter to be filed? Fortunately it's easy, and we don't have to try finding a secret mark on one cutter, or find where the continuous chain has been joined - you just need to find the shortest one.

There's a very simple rule to this, and it's that when you have finished filing all of your cutters, they must be the same length. If they are not, you'll find that the chainsaw will not cut straight and it's disconcerting to find your chainsaw has cut the timber in a graceful arc.

If all your cutters are the same length, then take another look and see if any are more damaged than the others - if so, tidy these up first.

Once you've found the shortest / most damaged cutter, it's time to sharpen it; place the saw in a vice to keep it steady, don't try to hold it between your legs or sit on it. Ideally use a file guide to ensure that you get the right angle - don't be tempted to guess what 30^o or 25^o looks like. The angle shown on the guide should be in-line with the chain / guide bar.

Once you've sharpened this first cutter, measure the length of the cutter (shown in the picture, right). You can use a nut and bolt for this if you're a cheap-skate you want to (I do), but obviously calipers are more accurate.

Now for the Dave's 'Tip Of The Day' - mark the cutter you've just started with. It's your chance to colour in - just use a permanent marker and colour the top of the cutter (called the top plate). This will ensure that once you sharpened all the others and you've worked your way around the chain, you won't carry on by filing the one you started with!

Only file the cutters that are on the other side of the bar to the one you're standing on. If you notice the arrangement of cutters on the chain, you'll see that they are on alternate sides - you sharpen all those on one side, then turn the saw around and do the other.

Once you've completed all the sharpening, you must remove the burrs that have formed during your filing; this is easily done by rubbing a block of wood up against the cutters. This will get rid of the wire edge and ensure that the chromium plating is not removed when you start cutting for real.

So we've now got sharp cutters and de-burred them - the depth gauges come next.