CHAINSAW CHAIN SHARPENING WITH A BENCH CHAIN GRINDER
There are a number of items to be considered when sharpening a saw chain with a bench mounted chain grinder. There are a number of manufacturers who sell grinders. The operating procedures vary from unit to unit, however the angles on the chain that must be maintained are the same. The angles vary depending on the type and manufacturer of the chain and a good grinder should be capable of sharpening most chains, with the exception of square ground chain. The following is a guide for using a chain grinder.
1. TOP PLATE FILING ANGLE (Figure 1)
This is controlled by setting the chain vise on the grinder to specified angle to the right of zero and sharpening all the right hand cutters. Then rotate the vise to the same angle to the left of zero and sharpen all the left hand cutters. A left hand cutter is illustrated.
2. TOP PLATE CUTTING ANGLE (Figure 2)
This is set by angling or rotating the wheel (and motor) to the correct angle so that the wheel contacts the cutter from the side. This varies depending on type of chain from 40º to 60º (60º is most common). I have found that using an angle of 55º produces a slightly faster cutting chain. However since this produces a thinner edge the chain dulls a little faster.
3. SIDE PLATE ANGLE (Figure 3)
This the most difficult angle to visualize and control. I refer to it as the hook angle. In other words it is how much hook the top plate of the cutter exhibits when you view the cutter from the side. If using a file you would control this angle by choosing the correct diameter file. A smaller diameter file will produce a smaller side plate angle or more "hook". A larger diameter file will produce a larger angle and it may approach 90º.
There are a couple of ways to control this angle with a bench grinder. There are four common wheel thickness, 1/8", 5/32", 3/16", 5/16". (5/16" wheels are used for large chain like that used on a harvester and won't be used for most saw chain encountered) The thinner the wheel, the smaller the side plate angle created. Also when using an Aluminum Oxide wheel the way you shape the wheel will affect the angle. You do not shape a Borazon or Diamond coated wheel. I have found that varying the top plate cutting angle will affect the side plate angle to some extent. There is a trade off in using the top plate cutting angle to control the side plate angle and the best way to create the correct side plate angle is to use the correct thickness wheel. it is best to use the angles specified by the chain manufacturer. Stihl recommends a side plate angle of 85º Oregon, depending on the type of chain, recommends an angle from 60º to 85º. When using a Al2O3 wheel shape the edge of the wheel to a smooth radius using the template supplied with the grinder.
Unfortunately as you sharpen the cutters not only do they get shorter, the height decreases and it becomes more and more difficult to keep the side plate angle below 90º.* My experienced is that with a smaller angle the chain cuts faster and requires less horsepower and creates less vibration. However with that said for, safety reasons, it is best to stick with the specifications recommended by the chain manufacturer.
1.) The depth that you grind into the cutter is important. Don't grind below the original gullet in the cutter. It is best to keep depth just above the gullet. If you grind too deep you can hit the tie straps and weaken the chain.
2.) Always set the depth gauge controls after you sharpen the cutters. The depth gauge controls are often referred to as the rakers. These control the thickness of the wood chip that cutters take or shear out. Too low rakers and the chain will "bite" to deep causing vibration and stalling the chain. Too high rakers and the and the chip is thin and cutting speed is reduced. For most common chain types the rakers are set 0.020" to 0.030" below the top plate. The rakers are set with a flat file and a depth gauge. I prefer Oregon depth gauges that come in a variety of forms to match their chains. However their gauges can be used on most commonly available chains. (Stihl, GB, Carlton, Windsor, and etc) It is best to file the depth control from the outside of the cutter in. Also once you have filed the top of the depth control round it to approximately its original shape.
3.) I recommend that you thoroughly wash the chain in mineral spirits and dry before sharpening. This helps the wheel from "loading up" with oil and wood dust. Once you have sharpened the cutters and filed the rakers, soak the chain in oil for a hour or so and hang it up so the excess oil drains off. Pre-oiling the chain prevents a "dry" start up on the saw.
4.) Keeping the chain tensioned properly is also important. I recommend that you keep it quite tight. (Assuming you have a sprocket tip bar) To check for proper tensioning try pulling the chain out of the bar groove. You should not be able to pull the drive links out of the bar using moderate force. It is a good idea to use gloves when performing this test. Once installed and tensioned, using gloves, pull or rotate the chain around the bar. It should move smoothly and not catch. If it does catch carefully check the bar and drive sprocket or rim for wear or damage. Don't start the saw until any repairs are made.
* If you look at the side view of most cutters the height of the cutter decreases from front to back. This design allows the cutter surface behind the sharp edge to clear the uncut wood.
All drawings on this page are from the Oregon Maintenance and Safety Manual.