MGoodwin
ArboristSite Member
I started a new thread on the matter because I want to focus on the reasoning for using raker angle versus raker depth. Below is a post from BobL (I think there was a picture but it wasnt showing up) outlining the use for raker angle but I am not clear on the exact reasoning. I am all for it though I am unconvinced. Below that is my reasoning for using raker depth.
FROM BOBL:
1. Chip size and hence cutting speed is determined by cutting angle (angle between raker - cutter -wood) which is controlled by the raker depth.
Few chainsaw users realize that filing to constant raker depths (eg 0.025") over the life of a cutter produces increasing smaller cutting angles and hence reduced cutting speed. IMHO this plays into chain manufactures hands because it usually results in users buying a new chain before they need to.
In this picture I show a new and well used cutter filed to constant raker depth, the red line.
The blue line shows the reduced cutting angle resulting from using a constant raker depth.
To compensate for this the raker needs to be dropped even further. Carlton fileoplate guides do this automatically but fix to a constant angle so if you want a slightly different angle you have to do it manually.
I adjust my rakers height by first measuring 3 or 4 gullet widths (green line on picture) with a vernier caliper. I then divide the average gullet width by 10 and use that as my raker depth for the whole chain.
Because the length of the green line increases as the chain is constantly resharpened the raker depth increases producing a constant angle. The number used to divide my gullet width by is different for different type of wood, I use 10 for Aussie Hardwood but softwood I use 9.
Eg a new 3/8 chain has a gullet width of around 0.25" so divide by 10 gives 0.025". Near the end of its life the gullet can be 0.45" - again divide by 10 gives 0.045". I know some people will baulk at the thought of a 0.045" depth but provided they are all the same it should still produce smooth cutting
Most saws with used chains that people bring me to look at because they are are not cutting have this problem.
Now, what about raker shape??
My take:
Raker height setting: it has been argued that a progressive raker depth is the appropriate methodology. I have been looking around at chain manufactures sites etc and all I have found is the rakers determine the depth of cut, regardless of the angle between the raker and tooth. That’s why we have depth gauge tools that reference off the tooth (though there seems to be one or two that use raker angle?).
In the CS101 post by BobL detailing raker depth/ raker angle (fantastic write up to be sure) and the above post, the argument is made that the angle should be maintained, not the depth relationship (for example .025”). To maintain a constant angle through the life of the chain, would be to constantly increase the depth (which BobL posted depths using this process at one point). Seems to me the only relationship that matters between the raker and tooth is the depth. My reasoning is pretty straight forward: if one were to sight down the length of the bar, the only measurement you would be able to determine is the height difference between the top of the raker to the top of the tooth (raker depth). In other words you would not be able to tell the raker angle. Sighting down the bar is the same approach the teeth interact with the wood, hence why I think depth is the correct parameter and not raker angle. Because the wood is cut “head on” relative to the tooth, not the angle established between raker and tooth, I am not seeing how this measurement is useful.
I am hoping that BobL, or anyone, could explain why raker angle is the correct parameter to use when sharpening/maintaining chains. Thank you very much for your insight.
FROM BOBL:
1. Chip size and hence cutting speed is determined by cutting angle (angle between raker - cutter -wood) which is controlled by the raker depth.
Few chainsaw users realize that filing to constant raker depths (eg 0.025") over the life of a cutter produces increasing smaller cutting angles and hence reduced cutting speed. IMHO this plays into chain manufactures hands because it usually results in users buying a new chain before they need to.
In this picture I show a new and well used cutter filed to constant raker depth, the red line.
The blue line shows the reduced cutting angle resulting from using a constant raker depth.
To compensate for this the raker needs to be dropped even further. Carlton fileoplate guides do this automatically but fix to a constant angle so if you want a slightly different angle you have to do it manually.
I adjust my rakers height by first measuring 3 or 4 gullet widths (green line on picture) with a vernier caliper. I then divide the average gullet width by 10 and use that as my raker depth for the whole chain.
Because the length of the green line increases as the chain is constantly resharpened the raker depth increases producing a constant angle. The number used to divide my gullet width by is different for different type of wood, I use 10 for Aussie Hardwood but softwood I use 9.
Eg a new 3/8 chain has a gullet width of around 0.25" so divide by 10 gives 0.025". Near the end of its life the gullet can be 0.45" - again divide by 10 gives 0.045". I know some people will baulk at the thought of a 0.045" depth but provided they are all the same it should still produce smooth cutting
Most saws with used chains that people bring me to look at because they are are not cutting have this problem.
Now, what about raker shape??
My take:
Raker height setting: it has been argued that a progressive raker depth is the appropriate methodology. I have been looking around at chain manufactures sites etc and all I have found is the rakers determine the depth of cut, regardless of the angle between the raker and tooth. That’s why we have depth gauge tools that reference off the tooth (though there seems to be one or two that use raker angle?).
In the CS101 post by BobL detailing raker depth/ raker angle (fantastic write up to be sure) and the above post, the argument is made that the angle should be maintained, not the depth relationship (for example .025”). To maintain a constant angle through the life of the chain, would be to constantly increase the depth (which BobL posted depths using this process at one point). Seems to me the only relationship that matters between the raker and tooth is the depth. My reasoning is pretty straight forward: if one were to sight down the length of the bar, the only measurement you would be able to determine is the height difference between the top of the raker to the top of the tooth (raker depth). In other words you would not be able to tell the raker angle. Sighting down the bar is the same approach the teeth interact with the wood, hence why I think depth is the correct parameter and not raker angle. Because the wood is cut “head on” relative to the tooth, not the angle established between raker and tooth, I am not seeing how this measurement is useful.
I am hoping that BobL, or anyone, could explain why raker angle is the correct parameter to use when sharpening/maintaining chains. Thank you very much for your insight.
