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.

Working Edges: Part One.

Post number three in this quick look at common sharpening problems takes a closer look at the working edge of the cutter. This is the crucial bit that slices through the wood and so it must be sharpened correctly. I've seen a number of common errors when filing the cutters and getting the working edge correct is probably the most difficult. Click on the jump to find out a bit more...

There are a number of things that need to come together to end up with a good sharp chain that's capable of cutting effectively and efficiently. When we sharpen a chain we need to know:

1. the file size;


2. the filing angle;


3. the depth gauge setting.

We've already seen in the previous post that selecting the wrong file size will affect the side plate angle, or the amount of hook, given to the cutter; and this time we'll have a look at the issues surrounding the filing angle.

The filing angle, given by the manufacturers, lets you know the best angle for the type of work that the chain is to be put to. For example, a crosscut chain will have a filing angle between 25^o and 35^o, whereas a ripping chain is much shallower - the ideal is 0^o but values in the range of 5^o to 15^o is more common. This is because of the different way the cutter has to remove the wood when cutting across, or with, the grain. Cutting across the grain (cross-cut) the cutters must be set up to sever the fibres, when cutting along the grain (rip-cut) the cutter must essentially chip the wood away. We'll take a closer look at rip cutting and cross-cutting in a later post and see how it actually works.

Back to our filing angle; there are several ways of filing the cutter - from using just the file on its own, to using a Dremel with an attachment, through to the professional grinding wheels for accurate setting. Each has it's own merits and drawbacks (perhaps that could form another post in the future!). Here, we'll stick to using the good ol' file with a file guide.

The potential problem with using just the file is that you have no control over the height that you are filing at, making it all too easy to set the incorrect side plate angle. The file guide, used properly, should reduce the chance of this - notice that it doesn't completely alleviate it as you can still place it incorrectly or put too much pressure down on it. But it helps, and it's also got the lines etched in to it to make lining it up to the correct angle a simple task.

Stihl recommend a filing angle of 30^o with their Rapid-Micro and Rapid-Super chains which makes it easy to remember, but you need to be a bit more careful with Oregon chains, even those with the same identifier on them. An Oregon #21 or #22 chain could have it's filing angle set to either 25^o or 30^o depending on whether it's a 'round ground chisel' chain or a 'micro chisel' chain.

Once you know the angle, the problem then is that it can be hard to achieve if your filing stroke is not even. The picture at the top of this post shows what happens if you change the angle right at the end of the stroke; you can see that the working edge of the cutter is no longer straight. To correct this, make sure that you keep your filing stroke completely straight from the beginning to the end, and maintain an even pressure.

In the next post we'll continue with the working edge and the difference in shape between a chisel cutter and a semi-chisel cutter. Chisel cutters tend to be very easy to file with a straight edge all the way across, but time and again I see semi-chisel cutters not done to their best, so we'll pick up on this and have a look why...

Name Your Chain...

Until now, I've tried to keep it as unconfusing as I can - but I'll forgive you if you lose it a bit on this one. It's not(?) hard, it's just that each manufacturer has it's own terminology and that leads to confusion.

So, let's take a look, after the jump, at what all these odd terms that we find on the filing tables mean...

Whilst we were looking at the Oregon filing table did you notice that they didn't refer to the cutter profiles using the same names as we used earlier? No? Look again.

Let's take a look at the list below to see our naming convention, along with Oregon's (in red) and Stihl's (in green):

• Chisel: Round Ground Chisel: Super


• Semi-chisel: Micro Chisel: Micro


• Chipper: Chipper: Standard

Stihl also refer to their cutters as normal height and low profile, for which they use the terms "Rapid" and "Micro" respectively.

Chain components...

The chain you use for sawing will be made up of just a few components - but those components have a bearing on what the chain will be best suited to, and how safe it is.

Although there are many different types of chain, made for particular applications such as rip-cutting, cross-cutting, metal cutting, chains (for the moment at least) can be divided in to standard chains and safety chains.

A standard chain has the following components:

• Cutter: this, as the name may suggest, cuts the timber - but it also regulates how much timber is cut.


• Tie-Strap and Rivets: these hold the components together and the chain gets its flexibility from the use of rivets, in the same way a bicycle chain does.


• Drive Link: this performs several functions as it transfers drive from the engine, cleans the guide bar groove as the chain rotates and carries the oil to lubricate the chain and bar. This link must match the bar in use as several different sizes of chain are available.

The components above form a standard chain, but there is an additional chain component that can add to the safety of this item by smoothing out the cutting action, reducing vibration (and therefore whitefinger) and reducing the chance of kickback. This component is called a Guard Link and is really a modified drive link. This link has a sloping top, and it's position in front of and alongside the cutter helps the lift the wood up to the cutting edge.

Cutters come in a variety of profiles, which are best suited to particular applications and each has it's own advantage and disadvantage.

• The chisel profile is good for use in softwoods and it has a fast cutting action to slice through the timbers. This cutter profile is prone to dulling quickly and is therefore less durable than other types of cutter.


• At the other end of the extreme is the chipper profile, which is ideal for hardwoods, but has a slower cutting action. However, the advantage of this cutter is that it is more durable than the other types - and that potentially means less sharpening :-)


• In between these two types is the semi-chisel profile - this is a good all-rounder balancing the speed of cut of the chisel, with the durability of the chipper.

Next post... pitch and gauge.