Carbide tool grinders.

[Highpower]

There is a set of videos (5 parts) on YouTube that someone made showing how he made some improvements on his "carbide tool grinder" that a lot of home/hobby metalworkers have. It is a clone of a Baldor "500" grinder.

http://www.youtube.com/watch?v=lSi3lucyR...B4341A8C46

I viewed those videos right after I purchased my grinder some time ago and set about doing the same operations on it. While it did improve the performance somewhat, I still had a pretty good vibration in my grinder at times as the spindle was speeding up or slowing down when turned on or off. At certain RPM’S the grinder would shudder as it passed through its "natural frequency". It was bad enough that it would cause a brand new incandescent bulb in the light fixture to burn out the filament every time I turned off the grinder. I quickly learned to use a CFL bulb. (lol)

At that time I basically skimmed the surfaces on the hubs to true them up, and touched up the trunnions with some sandpaper on a flat surface and called it good enough. Well, it wasn’t “good enough” after all. So recently I tore the grinder completely apart to give it a more serious effort. These are just a few of the things I noticed and tried to improve on…

I’ve been told that the reason for many failures of these Asian electric motors is because the factories often to not properly insulate the stator windings (if at all) as a cost saving measure. So I opened mine up to have a look. While it did have a very light coating of varnish on the coils, they certainly were not bonded together in a solid mass like higher end electric motors. I called a few local electric motor service companies in town and found ONE that was willing to clean up the stator assembly, dip it in a heated varnish tank, and oven bake it afterward to cure and harden the insulation. That is… IF I removed the stator from the motor housing myself. (Press fit.) Estimated cost $30 - $40.

To try to save a few bucks, I thought I would give it a try myself and bought an aerosol can of clear insulating varnish (about $6) and started spraying. It was thin. Like water. Let it dry, and spray another coat. And another. And another….



Growing tired of this, I did a little more research and found out that there were a couple of different formulas for this insulation and moved up to the next higher viscosity, (Red) A few more coats of that and I was finally satisfied that the coils were sufficiently saturated and held tightly together. Time will tell how it holds up. I did have pictures of all of this, but seem to have lost them.

The next issue was the spacers used for locating the hubs on the motor shaft. Roughly machined and WAY oversized on the ID. They certainly didn’t help in keeping anything balanced by sitting off-center on the shaft. (0.747” OD.)



I turned some new spacers that are a snug slip fit on the shaft. No more flopping around and wobbling.



Even after truing up the original hubs previously, I wasn’t happy with them because I could still see voids in the castings. The mounting holes weren’t drilled very accurately either and the bolt circle pattern was off kilter, making it hard to bolt on a grinding wheel. I had purchased a diamond wheel a long time ago to put on the grinder for touching up carbide bits, but I never did install it. The diamond wheel is 3X heavier than an aluminum oxide wheel, which is a lot of mass to spinning at 3400 RPM. So I set about making some new hubs from some solid 6061 round stock.



You can see the voids in the lower two original hubs.

I went back and squared up the table parts and the wheel housings on the mill this time, making sure all the surfaces were flat / square / parallel to each other. The housing surfaces were going off at different angles causing most of the problem tilting the tables up and down. I also partially counter-bored the wheel housings around the mounting bolt holes because they are so close to the edges, the bolt heads rubbed on the sides making it nearly impossible to get a socket wrench on them.



So here it is, all back together, and greatly improved. The first thing I notice when turning the grinder on now is that it takes a lot longer to spin up to speed now due to the extra weight of the diamond wheel. The motor is working extra hard to get that mass moving now, so I’m sure the magnetic fields pulling on those windings are extra strong now. Hopefully my DIY insulation job is up to the task. I do know I’ll feel safer with the solid hubs hanging onto those wheels though.



For what it’s worth…