Chain back clearance angles

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Albert Beerstein

stihl learning
Joined
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Been playing with various chains and measuring everything, trying to find why sharpening results are sometimes inconsistant, but realised I had overlooked this: does it make a difference?

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these are the angles of various chains that I have :-
stihl picco .050 11.9°

stihl 3/8 chisel 11.7°

carlton 3/8 semi

carlton Lo Pro semi

carlton 3/8 chisel 8.5°

oregon chisel 3/8 11.5°

oregon chisel skip 3/8 11.5°

windsor chisel skip 3/8 9.5°

Johno & Jono semi 3/8 ( chinese chain sold here) 12°
 
Is this the reason some chains cut good and are well liked (E.G. Stihl and Oregon)?

A more acute back clearance angle would be the limiting factor for depth of tooth cut into wood, larger back clearance angles would allow the use of higher depth gauges for the same cut distance into the wood ( in a direction perpendicular to the bar). - the tooth could travel further into the wood before the top plate became level to the direction of travel then steered the cutter back out of the wood?
 
As far as I'm aware the top plate angle is set on cutter manufacture Ie when cutter /drive links made up it is a set angle the lower back end being lower is all involved in the cutter performing well the usual method of having a good cutting chain is correctly sharp cutters & correct raker depth race saw guys have their own usually secret sharpening angles etc. I will stand corrected but don't think the angles you speak of have any or very little effect on cutting capability
 
Is this the reason some chains cut good and are well liked (E.G. Stihl and Oregon)?
A more acute back clearance angle would be the limiting factor for depth of tooth cut into wood, larger back clearance angles would allow the use of higher depth gauges for the same cut distance into the wood ( in a direction perpendicular to the bar). - the tooth could travel further into the wood before the top plate became level to the direction of travel then steered the cutter back out of the wood?

Interesting "point" you bring up there AB.

Whatever the back angle is , it is a fixed parameter for a give chain, and along with the TPCA, contributes to the overall point-ness of a cutter.

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The extent to which a cutter penetrates wood is perhaps surprisingly less affected by the point-iness of the cutter edge and more by the raker angle.
If the raker angle is too low, it doesn't matter how pointy or sharp the cutter is (i.e. what the back angle is) the cutters will make dust because the raker angle isn't allowing for the cutter to make significant penetration into the wood
Screen Shot 2017-11-05 at 3.39.46 pm.png
Few folks realise that chainsaw cutters do not always slide along the top of the bar. Instead cutters bite into the wood is determined by the raker angle. While the cutter takes its first bite the cutter rocks on the raker which also very slightly forces the rocker to penetrate the wood and then the cutter rocks further into the wood. This process continues until the chain tension snaps the chip out and the chain back onto the bar. This process happens to varying degrees for groups of 3-4 cutters with the chain porposing up off the bar in waves. The extent to which the cutter ultimately bites into the wood is determined by how far the raker will let it rock and the overall point-iness of the cutter. So yes the back angle does ultimately contribute.

The largest difference between the back angles you have listed above is 5º. This can be easily compensated for by adjusting the TPCA or hook. However, I doubt anyone compensates for this deliberately - usually they will follow a chain makes recommendation on file sizes or grinder angles and experiment about those recommended values. When it does matter is if someone switches between chains and uses a filing or grinder setup for one type of chain on another. In harder woods you may even wish to use a less pointy cutter (less TPCA) so the chain lasts long through a milling cut before it gets too blunt.

What a higher back angle cutter may limit is over all chain longevity. At the very end of its life, a cutter with a higher back angle may have its edge so low on the chain that the raker will have to be filed down to next to nothing to maintain an adequate raker angle. This will make a cutter able to hold and clear less sawdust. I think some chains have marks on the cutters below which you are not supposed to use them although you could probably go a bit further than the lines. In contrast a Carton chain can be used until the cutters start breaking off which is well past where those marks appear on other chains.
 

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