Thread: a bush fix

What patches, they look normal to me?

I was looking at the difference in the "polishing" of the raker and cutter, there seems to be a difference in the amount of "polishing" on the 3 cutters pictured, the middle one seems to have the least, and theres a definate line along the middleish of the cutter. It doesn't matter in any specific way I don't think, but there is a difference and just curious if anybody else has observed this

Originally Posted by pjt

I was looking at the difference in the "polishing" of the raker and cutter, there seems to be a difference in the amount of "polishing" on the 3 cutters pictured, the middle one seems to have the least, and theres a definate line along the middleish of the cutter. It doesn't matter in any specific way I don't think, but there is a difference and just curious if anybody else has observed this

OK, now that I look closer I see the raker depths are not the same

The cutter with less shine has a cutter length of raker depth of ~0.057"
The cutter with more shine has a raker depth of ~0.065"

A lower cutter will dive further into the wood and be loaded up more than a higher cutter. The loaded up cutter creates more sawdust and bigger chips that escape below the cutter making it shine more.

It looks like you are running gullet width to raker depth ratios of about 7, which is pretty low Pete. If it's cutting fine it probably doesn't matter that much until the cutters gets short when they could snap off. If it was me I'd try to get the ratio up a bit more.

I also note the cutters don't have a lot of hook so the chain is probably not too grabby, but if a normal hook was applied the chain would really grab at those raker depths.

Yep that all makes sense Bob, results of wear/polishing/scoring can all be a tell tale sign of what's going on, just have to understand the pattern left behind.

I reckon that the difference in raker height is a function of field sharpening as opposed to doing it on the bench at home, it happens, I'll have a quick check of things tommorrow although as u say the chain is nearing the end and I tend to not worry too much at this point. I did notice that as the cutter length was decreasing I had to pay more attention to achieving a suitable hook angle, it seems the shorter the cutter becomes the file tends to ride up out of the gullet, to achieve the 10° from (horiz) (I forget what this angle is called) the round of the link tends to get filed as well, which I try not to do which may contribute to the reduced hook angle.

Having said all that tho the chain is cutting quite well, not too grabby, reasonable chips and a good rate of travel, even with a full 900mm width of cut in that raintree fork I posted some pics of a while back

Peter

Originally Posted by pjt

I reckon that the difference in raker height is a function of field sharpening as opposed to doing it on the bench at home, it happens, I'll have a quick check of things tommorrow although as u say the chain is nearing the end and I tend to not worry too much at this point. I did notice that as the cutter length was decreasing I had to pay more attention to achieving a suitable hook angle, it seems the shorter the cutter becomes the file tends to ride up out of the gullet, to achieve the 10° from (horiz) (I forget what this angle is called) the round of the link tends to get filed as well, which I try not to do which may contribute to the reduced hook angle.

I usually avoid touching the rakers in the field. Like I said in another post, I drop the rakers below the recommended depth and so during a cutting day I only touch up the cutters and by the second half of the day the rakers are running right and by the end of the day they are probably a touch under. Then that night I flip the bar and swap the chain and set the rakers of the old chain off the bar.

A "gullet width"/"raker depth" ratio of 10:1 produces a "cutting angle" of around 6º.
Your "gullet width"/"raker depth" ratios are around 7:1 which translates to a a cutting angle of around 8º which is pretty high - but is counteracted by a relatively smaller hook. I reckon if you added more hook the chain would grab too much but would probably self feed better if you let the rakers stay a touch higher and add more hook.

Having said all that tho the chain is cutting quite well, not too grabby, reasonable chips and a good rate of travel, even with a full 900mm width of cut in that raintree fork I posted some pics of a while back

Great!