Reducing Bench Grinder Vibration

The Problem

If you have had difficulty getting grinding wheels balanced, this article may prove to be helpful. I have a 6 inch Craftsman bench grinder with a 1/2" arbor. That means that when I buy a new grinding wheel, it will likely have plastic bushings to reduce the 1" hole in the wheel to a 1/2" hole for the shaft. Those bushings can have a lot of play in them, causing a runout on the grinding wheel that is difficult to adjust. In addition, the cup-shaped steel washer seated on the too-small shoulder on the shaft is not enough to positively square the washer when the grinding wheel is tightened. This combined with the fact that the washers themselves may not be formed well results in a wobbling grinding wheel. The combined result: eccentricity and wobble. If you read forums about grinder vibration, it seems like the 6 inch grinder is more susceptible to vibration than an 8 or 10 inch. I suspect that it is because they have larger diameter arbors, and therefore less bushing play and larger shoulder area for washer squareness. I nearly scrapped my grinder and bought an 8 inch, but decided instead to put my lathe to work and build some bushings to resolve it.

The Solution

The solution is to build a part that will serve as both a precise bushing and square washer, leaving little room for variation when installing the grinding wheels. This part virtually eliminates eccentricity by being a tight-fitting bushing. The wobble is mostly suppressed as well, because the new washer is held square to the shaft by the long bushing-shaft fit rather than a tiny shoulder on the arbor. If your clearances are tight, you will have a minimum amount of vibration on your grinding wheels. The idea was not my own. I saw it on someone else's website, but with a much more complex process, so I wanted to simplify it. If you have a lathe, this is a pretty easy project to improve an otherwise useless grinder. Below are the basic steps to take in fabricating the bushings.

BEFORE AFTER

The Process

All you need for this project is a lathe, about four inches of 2 inch aluminum or steel round stock, a 1/2 inch drill bit, center drill, and left and right hand turning tools, a narrow-angle turning tool (like a thread cutter), and a good hacksaw. I bought two feet of 2 inch 6061 extruded aluminum online for $52 shipped.

Step 1 - Chuck a four inch long piece of stock in the lathe and cut a clean surface on the outside.

Step 2 - Cut the 1" arbor per the drawing.

Step 3 - Face the washer. The LH turning tool you use to cut the arbor will not result in a flat washer face, so it has to be faced with a RH turning tool.

Step 4 - Cut a recess inside the washer face. I used a 60 degree external thread cutter set at about 45 degrees to the work to make this cut. When next to the arbor, just touch off the arbor face then cut into the washer. I was able to start at the arbor, cut into the washer, then move the cross-slide out, cutting backwards into the washer face. This may not have worked on steel, but aluminum with thin cuts worked great. This portion doesn't need great precision, just get 0.020" or more depth cut into the ID of the washer, and you won't have to worry about it putting pressure on the center of the grinding wheel.

Step 5 - Cut a shallow groove for the hacksaw, allowing about 0.020" extra to be faced off later.

Step 6 - Drill a pilot hole using a center drill.

Step 7 - Drill a hole using a small drill bit (1/4" or so) a little more than the depth of the part.

Step 8 - Drill at least one more progressively larger hole. I only did this once.

Step 9 - Drill the final hole using a 1/2" drill bit. A smaller bit and a reamer would be better, but I didn't have a reamer.

Step 10 - With the lathe turning, carefully use the hacksaw to saw the part off, staying in the groove you cut in step 5. The use of lubricant will speed this process considerably.

Step 11 - Make the second part (2 pieces for one grinder) following the same steps as before.

Step 12 - Chuck the new part in the lathe and face the saw-cut surface with a RH turning tool.

Step 13 - Check the fit on the grinder shaft.

Step 14 - Check the fit in the grinding wheel.

Step 15 - Install grinding wheel and outer washer.

Below is the drawing.