I see a number of questions regarding chain angles from time to time so though I would put together this post explaining what each of the angles are, their purpose and effects of varying the angles.
I won't go into much detail about how to generate these angles. If there is enough interest I'll do that in another post.
Firstly a quote from the Carlton chain Manual.
It's not specifically directed to milling but it still applies - note the emphasis on
rakers rather that
cutter edge angles as being the main source of chain problems
This following figure is modified from the Oregon chain manual and I will refer to each of these below.
RAKER ANGLE (RA)
The Depth Gauge setting I replace by what I call the raker angle. It's a term use to describe the angle between the wood, cutter edge and top of the raker. RA is a "roll your own" angle since optimal RAs depends on a number of factors like, saw power/torque, drive sprocket pin count, chain, hardness/dryness of wood, length of bar or how many cutters are in the kerf, etc.
The RA works together with the TPFA (See next paragraph) to generate a highly desirable self feeding saw.
I recommend starting with what most new chains have which is a RA of ~6º and then vary up or down from there.
I use about 6.5º for an 880, with an 8 pin drive sprocket, full comp 3/8 chain, in green Aussie hardwood.
The higher the RA the greater initial bite the cutter makes.
Too high a RA and the saw will struggle, increase chain vibe, bar, chain saw wear, and even stall low a powered saw
Too low a RA will result in slow cutting and lots of fine dust frustrating operators causing them to push harder and increase bar and chain and powerhead wear.
Using a 0.025" raker depth during the whole life of the cutter continually decreases the RA and is the main reason why I see operators throw away perfectly good chains because they do not appear to be cutting even when the cutters are razor sharp.
Using a consistent RA means you do not have to worry about keep the cutters the same length since each cutter cuts according to its RA and TPCA rather than its length
TOP PLATE FILING ANGLE (TPFA)
This is traditionally 20 - 35º for cross cutting and les,s eg ~10º, for milling.
A higher TPFA will pull the chain slightly more sideways in the cut hence cutting a slightly wider kerf and vice versa.
The reason for using a higher TPFA for cross cutting is because it involves cutting across wood fibres leaving fibre ends hanging and occupying some space in the kerf. When the chain is blunt the fibres are often torn more than cut and the furry fibre ends can clog a kerf restricting adequate clearing of sawdust making more work for the chain to clear the dust.
Will Malloff uses 0º on his chains. This is fine as long as they are not less than 0º. If they are less than zero the cutter may tend to slew off the cut and not cut as efficiently. This is why I recommend some angle rather than zero. I'm not fussed about this angle being too accurate and my cutters are normally 10º +/- 5º
There is a lot of discussion about TPFA being a significant influence in the finish obtainable by a CSM. I reckon that the stiffness of a CSM and the way an operator guides the saw down the log are much more significant that TPFA. If the mill is a sloppy-joe and the CSM jockey seesaws the mill down the log with uneven pressure, starting and stopping to put in wedges and ramming the CSM into the cut this will produce a far worse finish than a higher TPFA. Most of my chains start out as regular cross cut and they are filed to a TPFA of ~10º over successive sharpening. If I am careful with my mill I see no difference between the finish generated by low or high TPFA.
TOP PLATE CUTTING ANGLE (TPCA).
TPCA determines the hook which combined with RA determines how effectively the saw/chain self feeds.
TPCA variations have the same effect as RA
A cutter with a high TPCA will have a similar effect to a low RA. High TPCA generates a cutter with a squarer cutting edge or less hook which goes blunt slower but provides poor self feeding.
If the TPCA is >90º, then a what is called a back sloped cutter is generated, which will cut poorly or not at all which often results in operators pushing saw harder leading to high bar and chain wear and powerhead overloading and overheating.
If the TPCA is too shallow then the edge of the cutter will also be too fragile and easily break off/wear so the chain will become blunt quickly.
TPCA is a result of the size of the file and it's height above the top of the cutter (or radius of the edge of the grinding and angle of the grinder used).
Like RA, TPCA is a "roll your own" angle since it depends on a number of factors like, saw power/torque, drive sprocket pin count, hardness/dryness of wood, length of bar or how many cutters are in the kerf, etc.
Will Malloff uses a quite shallow angle of 45º on 404" chain. Oregon recommends 50º for its ripping chain.
It's easy to set AN angle on a grinder but as the resulting angle also depends on the radius of curvature of the grinding wheel the actual angle obtained will not be what the grinder says it is. It is quite difficult to measure this angle on a cutter but on 3/8" chain I use whatever a 13/64" file in a 3/16" file guide generates because this seems to produce enough hook for the chain to self feed a little without knocking the edge about too quickly causing it to become blunt too quickly.
For newbies I recommend sarting with 50º and varying it from there.
SIDE PLATE FILING AGLES
This angle is not one that can be actively controlled as it is the result of the combination of TPFA and TPCA. Once these two are fixed this determines the side plate filing angle.
FILE GUIDE ANGLE
Finally comes the file guide angle. This is easy and I just go with what the chain manufacturer suggests.
Usually a slight angle of say 10º helps form a pointier tip on full chisel chain while for semi chisel chain no angle is needed.
I hope this is useful to someone.
Cheers
