Monday, January 31, 2011

Chainsaw Rakers

Well I spent the better part of four hours on Saturday sharpening the chains on my two 36" bars, getting ready for Monday's trip to Sechelt. Normally it takes only a couple of hours to prepare for each cutting session.

This time took longer because in addition to sharpening, I had to file down the rakers. This is an extremely tedious procedure, but needs to be done every 3-4 sharpenings else the teeth cannot 'bite' into the wood when cutting. I use a Dremel drill to hog each raker down to close to where it should be, and then use a file and a raker guide to get it bang on. I don't like the Dremel for sharpening the teeth though, I can't control it as well as I can a file.

I use ripping chain for cutting slabs. The main difference between ripping and normal chainsaw chain is the angle of the teeth. Ripping chains are normally filed to between zero and ten degrees, while a typical chainsaw chain used for bucking firewood say, is filed to about 30 degrees.

When a chainsaw is ripping, ie cutting a slab, it is effectively cutting end grain for the whole cut. And the saw's throttle is kept wide open for the whole cut, which may last five or ten minutes. So milling is about the hardest use a chainsaw can be put to in wood!

And of course there are many different types of ripping chain. I use two types, the subject of this particular blog entry is a bit unusual, it has two types of teeth on it, regular cutting/clearing teeth, and scoring teeth that have no top on them, they just score the wood to make it easier for the regular teeth. It's kind of hard to see the difference in the picture below, check out the top view in this link for more details.  Ripping Chain

I like this chain for a couple of reasons, I find it cuts a bit more smoothly than a chain with all regular teeth, and it allows the motor to maintain higher RPMs while cutting.  On the downside I do find it a bit fussier (ie dulls more quickly) and perhaps a bit slower. Of course, how sharp a chain is is way more important than anything else.

The picture shows the angle of a regular tooth in green and a scoring tooth in red. If you put your protractor to the screen you will find that the scoring tooth raker has an angle of about 9 degrees whereas the regular tooth is about 6 degrees. The cutting tooth raker is bang on, but the scoring tooth raker may be a touch aggressive.

Of course the whole measuring system falls apart quite quickly if the teeth are not a consistent height. And there is an element of 'eyeballing' that comes into play in the camera angle and in drawing the lines. Not to mention that the bar the teeth are sitting on has a slight curve in it.

I'll talk a bit more about tooth height in a future entry. Consistent tooth height is critical for several reasons.

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