With a little alteration an old auto piston becomes a grinder head for light and small work. Cut the piston skirt off just below the wristpin bosses. A portion of the piston wall is then cut away creating access for a belt drive, or a hole drilled in the bottom of the piston could allow it to be driven from below. This diagram shows the rear-driven aspect. The shaft is turned to fit the wheels and threaded for retaining nuts. Collars should be turned at the same time the shaft is made, and should very closely conform to the diagram here. The pulley is a standard type available at hardware stores in 1" or 1&1/2" size depending on the size of the piston and the overall project. Steel pulleys are better than the white metal available as standard fare in the hardwares today. Drill small access holes in the shaft/bearing receptacles, so that these bearings can be oiled periodically. On this model all that is required are two small holes drilled through the base and it can then be screw mounted to any bench or plywood plate. It may be necessary to elevate the grinder with base plates to create clearance for the belt. Check everything before final assembly. This is a good little lapidary type grinder, but needs to be mounted in a pan and have a hood covering the wheel if you are going to use it to grind rocks. Lubricate the lapidary type wheels with a pressurized water feed or spray bottle of water. Finally, before the shaft is made check and see what type of diameters you will be working with as far as your particular abrasive wheels are concerned.
Please read this in its entirety before attempting to build. Safety First. Always wear eye protection when working with shop equipment. No warranty is implied or given concerning this information. The action of the author is to portray tested information. The action of anyone else, whether aware of this information or not, is in no way to be construed as actions of the author. This information is safe for anyone with good mechanical and electrical aptitude.
Sturdiness and accuracy come together in this inexpensive roller bearing grinder, which you can make from an old differential assembly. This grinder will handle wheels up to 12” diameter, and can be configured in numerous ways, including floor stands or bench models. Except for the machined shaft, which goes where the axle went, and the wheel collars, all the work can be accomplished with hand tools commonly found in any shop. Have the shaft custom machined at a machine shop unless you can do your own work with a metal lathe. I think top $ spent for this piece would be about $40.00, and probably as much as half that. If you can go to a schools machine shop and get them to do it for you, you will save substantially, and its a fairly easy job to perform. Metal stock can usually be obtained cheaply at scrap yards. Use the diagram here to show the machinist what you want, and furnish them the sizes for your particular salvaged differential assembly. The shaft should be cold rolled steel, around 24” in length, and 1&1/2” in diameter. Cast Iron disks known as building washers are your best bet for the four grinding-wheel collars you will need. Have them machined as they are diagramed, with a 1/16th" recess on the interior face, the face against the wheel. This is important to do. It is also very important to have the collar faces machined perfectly parallel, so the wheel rides true. The center bore of the collars must create a snug sliding fit over the ends of the shaft.
To make the drive pulley, four hardwood disks are bored to a Drive Fit (Tight) over a bushing made from a 3" length of brass tubing with an inside diameter of 1&1/2". The wall thickness of the brass bushing needs to be at least 1/8" thick. Use glue between the hardwood disks and clamp tightly until dry. When finished drill and tap through this wheel and the brass pipe for a headless set screw by which to affix the pulley to the drive shaft. A couple of set screws, one at either end, is optimum. Line 'em up.
Quite a lot of cutting and other modification is necessary on the housing, and different areas need to be addressed depending on which model you are making, either overhead or rear drive. Refer to the drawings for suggested ideas. The parts rests and wheel guards can be configured for your situation, and with a grinder of this size and power (2000 RPM Max) the parts-rest assembly is a very good idea, and the wheel guards a MUST. With the casing apart you will need to drill holes for the various accouterments to be attached, so it is a good idea to pre-mark your wheel guard assembly and part-rest assembly before you dissemble the differential housing. You will also need to drill for grease fittings tapped over the roller bearings themselves. Because the holes will be drilled at an angle it is best to drill smaller and then use a reamer to enlarge them. In order to tighten these assemblies bolts effectively, sleeves are cut from 1/2 inch pipe that fit over the bolts holding the assemblies on. The ends of these sleeves that butt up against the housing need to be beveled for a straight fit. The wheel guards are attached to the flat stock supporting bar at the back of the grinder, NOT at the housing of the grinder itself, so care must be taken with measurements and final fastenings.
When assembling the unit be careful to align the interior parts of the roller bearing assemblies correctly, and if you make notes as you take it apart that could be very helpful. You will of course be including all the new parts as you do it, so patience will be good coin for you here.
1800 RPM is the suggested speed of this grinder, with 100 rpm either way, and washing machine motors are 1725 RPM. A pulley on the motor the same size as the grinders interior drive pulley will rotate the grinding wheel at that speed. Smaller wheels can be run slightly faster.
If this grinder is to be used for lapidary uses, modify the wheel guard to except a water feed, and mount the unit in a water tight pan.
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