The Madsen site has some great info, just working my way through it:
gotta avoid those "beaks"...
Q: Is it better to file or grind square ground chisel chain?
A: It is better to grind it. From what we see, most who square file don't do it well. Many don't realize (or admit) the kind of cutting performance they would enjoy if their chains were sharpened better. Square filing requires precise corner alignment and filing angles -- a level of accuracy that is hard to achieve by hand.
Q: Can you have a grinder set up with all the correct angles and still grind chains that cut poorly?
Chisel Chain Corner
A: Yes, corner alignment is critical. The working corner of the grinding wheel mist be aligned with the corner of the cutter's tooth. If the wheel is set too high, the chain won't cut well. In the wood, the chain will perform like a dull chain, even though you know you just sharpened it. If it is aligned too low, the chain will cut great, but it will get dull fast. The reason is: The cutter tooth will have a little "beak" on the top of the tooth. This little beak can be quite sharp, but has little support and dulls easily.
Q: Don't some people grind this way on purpose?
A: Some do, and if they are satisfied with the results, it's OK with us. They could get similar results from increasing the side angle or increasing the "back slope" on the side of their tooth. This will still feed aggressively but will give the cutting edges more support.
Another reason for "beaks" is it is difficult to align your grind perfectly on every tooth. Some grinders are not as accurate as they should be, the size of cutter teeth may vary slightly, and some grinder operators pay more attention to the process than others. Maybe another way of saying this is the accuracy "window" is larger for some than others. So, depending on what size "window" you work with, always try to align perfectly, but make sure that if you are off a little, you will be low. If you are slightly low, the chain will still cut well. If you misalign the corners and end up with the corner of grinding wheel slightly high, the chain will perform poorly.
Q: What are the best angles?
A: There are four main angles in the face of a square ground chisel cutter tooth. They are:
Outside Top Angle - This is the angle on the top plate of the cutter that you see when you look down on the top of the chain. This angle should be 15- 20 degrees sloped back. (0 degrees would be a right angle to the bar.)
Inside Top Angle - This is the angle of the face, inside the top plate. This angle should be 40-50 degrees. (0 degrees would be a right angle to the top plate.) If all this geometry doesn't make sense to you, just remember that the inside angle should be about 45 degrees.
Outside Side Angle - This is the angle of the side plate of the cutter that you see when you look at the chain from the side. This is the angle usually called "hook" by cutters. It should slope back up to 5 degrees. (0 degrees would be the plane of the bar.)
Inside Side Angle - This is the angle of the face, inside the side plate. This angle should also be 40-50 degrees.
.......But I guess if you're felling toothpicks you don't need the accuracy of hand filing .....:sarcastic:
