# Raker depths



## MGoodwin (Oct 8, 2014)

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.


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## MGoodwin (Oct 8, 2014)

Here is a little explanation visual: http://www.madsens1.com/bnc_how_wks.htm. If the picture is right, you'll notice the chip is lifted as the tooth cuts and would seem unaffected how far in front the raker is positioned.


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## Philbert (Oct 8, 2014)

Here is the BobL thread I think of:

http://www.arboristsite.com/communi...ly-progressive-depth-raker-generators.114624/

The issue is that the top plate of the cutter is sloped. As the cutter gets worn/used/filed/ground back, it gets _farther_ from the depth gauge and _lower_ than the depth gauge. So many people believe that maintaining a constant offset in height between the two (e.g. 0.025 inches) is not as effective as maintaining a constant angular relationship. The referenced thread goes into the angular argument quite a bit.

The File-O-Plate, Husqvarna roller guide, and new STIHL FG4 guides use this angular/progressive approach. One disadvantage is that some of these are chain-specific - they will not work with all chains. This is a problem if you run or sharpen lots of different chains. 

Apparently, Oregon used to make a drop type depth gauge tool with an adjustable offset, so that you could dial in a specific amount. A version of this tool is shown in the Art Martin thread: http://www.arboristsite.com/community/threads/art-martin-will-the-real-logger-please-stand-up.4932/ 

Other guys use a straight edge and feeler gauges. Or you can buy offset style depth gauge tools in .025, .030, and .035 and estimate accordingly.

Bottom line is what works for you.

Philbert


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## Philbert (Oct 8, 2014)

Post 505: http://www.arboristsite.com/communi...-the-real-logger-please-stand-up.4932/page-26

I suppose with a fine thread screw and some feeler gauges or gauge blocks to calibrate, you could make your own. Maybe even a piece of channel and a cheap dial indicator?

Philbert


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## BobL (Oct 10, 2014)

I think you maybe getting confused by what I mean by raker angle.

It's not the angle on just the top of the raker (although that that does have an affect and I could point to some posts about this) its the angle between the wood surface, the tip of the cutter and the topmost part of the raker.
In the picture below the ruler is sitting on the top of cutters.
The raker angle is the angle between the ruler and the blue line.

BTW The top of the raker should be slightly curved. If it has a flat top (even if it is tilted) the leading corner can dig into the wood and add more friction than necessary.

Of course the raker depth determines the raker angles, as does the gullet width so as the cutter wears, if a constant raker height/depth is used the raker angle becomes more and more shallow which kills cutting performance




With all respect to the Madsen's info that is a very much simplified description of cross cutting. In CS milling it's end grain cutting so it's the top plate doing most of the work. 
It doesn't matter wether it's cross or end grain cutting a CS cutter does not work like a wood plane. The cutter rocks its way into the wood as determined by the cutter angle and chain tension. The raker anIf a constant cutter depth is maintained during the life of the chain the amount of "rock" available to the cutter decreases and it just cannot bite enough wood no matter how sharp the cutter is.

Anyway I'm near done writing about this topic having written more than enough about it on more than one forum. 
If anyone doesn't believe me, grab yourself a couple of chains with well worn cutters and set the rakers to 0.025" on one, and set the raker angle to 6.5º on the other, and go cut some wood. 
Folks have given me old chainsaws telling me "it's not cutting" and when I give it back to them with just the rakers reset they think I have overhauled the saw.


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