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.