Sharpening & Maintaining Square-Ground Chisel Saw Chain
If we had a web cam in our shop, you could probably overhear one of our techs talking about sharpening or some maintenance aspect of square-ground chisel saw chain. It is something we talk about very frequently. The reason is: chain maintenance greatly effects the cutting performance of any pro saw.
If you are a user of square chisel chain or considering using it, you have probably discovered that there is not a lot of published information on the subject. Of the information that exists, much is handed down from user to user -- and fair amount of this is clouded with misinformation.
Many pro users ask the same questions and have similar problems. So, we have assembled frequently asked questions and our answers. Hopefully these will help you with a question you have, or expose you to an idea that will help you get better performance from your professional saw chain.
Frequently Asked Questions
Q: Does square ground chisel chain outperform round-ground chisel chain?
A: If cutting efficiency is what you are after, the answer is: yes. On most pro saws, square ground chisel chain will cut 10% to 15% faster than round ground chisel chain. Its sharp angles sever wood fiber more efficiently that any other type of cutter tooth. But, if maximum stay sharp ability and ease of filing are objectives, the answer is: no. Chisel chain dulls easily and is the most difficult to sharpen.
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?
A: Yes, corner alignment is critical. The working corner of the grinding wheel must 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, but 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 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.
For more information and a graphic, see our section on Sharpening Angles Of Square-Ground Saw Chain.
Q: What angle should that little angle be on the inside of the tooth -- you know, that little line that goes up into the corner where the top plate and side plate meet?
A: No, we didn't forget about this angle. Actually, it is formed when you align the corner of the grinding wheel with the corner of the cutter tooth and all the angles above are correct.
Q: Is it true this angle should line up with the corner of both plates on the inside and the outside of the tooth?
A: No, this angle only needs to line up with the outside corners. Where it ends up on the inside of the tooth doesn't make any difference. The thickness of the metal in the corner of the tooth affects where it ends upon this inside. Pay attention to the outside corner and the other angles. If they are right, don't worry about where this angle is on the inside of the tooth.
Q: Do I need to remove the gullets very often?
A: Yes, don't let them get longer than 1/8". When the gullet is longer, the "set" remaining in the gullet can rub against the wood. When this occurs, the gullet can keep the cutter's sharp corner from biting into the wood. With the gullet removed, the sharp corner becomes the most outward point and the tooth will "feed" well.
For more information and a graphic, see our section on Chain Gullets Explained.
Q: Should I run my rakers below the manufacturer's recommendation?
A: No, if you have to cut your rakers low, you are probably not doing a good job of sharpening the cutter teeth. While some do try, you can't make up for bad sharpening technique by cutting your rakers low. Well sharpened cutter teeth with no gullets and rakers set at the recommended height will produce cutter teeth that pass smoothly through the cut -- and when each tooth takes a smooth and even bite, the chain performs very well. This is what your sharpening and maintenance program is all about.