Grinder Takes Shape

I have my 2×72 belt grinder set up, more or less.

It has been an interesting project. To make it work, I had to choose between getting a new base for the grinder or making it work with my old abrasive cart, which is a Northern Tool cart that held my 1×42 belt grinder and bench grinder. In the end, I decided the smart thing was to try to jam both belt grinders on the cart. It’s easier to put the bench grinder on a new base than to start from scratch on a belt grinder base.

The motor I’m using is gigantic. It’s the old 2-HP Reuland motor I got for nothing (sort of). When I bought my first lathe, the unscrupulous dealer sold me the wrong machine, and he included a 1-phase motor instead of the 3-phase job he had advertised. He made a little effort to make things right, and that included shipping me the ancient Reuland. The shaft was banged up, so I took to Ebay and bought a beautiful new 2-HP Baldor, cheap.

I guess I can’t call it free, since the dealer still cheated me, but I didn’t pay for the motor.

When I first tried to use the Reuland, I had a hard time getting the lathe’s pulley mounted. Then it ran funny. When I took the pulley off and looked at the shaft, it appeared that someone had banged it pretty hard with a giant hammer or something. It had burrs and a big flat spot. I can’t even guess what kind of idiot does a thing like that to a top-of-the-line 3-phase motor, but I can tell you this much: it was an employee, not the owner of a company. People who pay for things don’t beat them with hammers.

When you bang on a piece of metal and make a depression, you also raise metal. The metal you displace from the depression has to go somewhere, so it usually rises up around the depression, forming a rim. I heard a master machinist describe this as “disturbed metal.” My motor’s shaft had disturbed metal around a big ding, so the pulley had a hard time sliding past it.

I got rid of that lathe a long time ago, and of course, the buyer cheated me out of a hundred dollars. I had it rigged up with a VFD, which I kept. The fact that I had a motor and VFD lying idle figured prominently in the rationalizations that enabled me to buy the new belt grinder.

When I tried to put the new drive wheel on the motor (to pull the grinding belts), it didn’t want to go over the damaged shaft, and the keyway in the shaft looked enormous. I assumed it was larger than the usual keyway for a 7/8″ shaft. It looked bigger than the corresponding keyway in the wheel. I figured I would have to broach a bigger keyway into the wheel.

I got the motor running, and I used the spinning motion to help me file the bumps off the shaft. I then sanded it. After that, the wheel went right on, and surprisingly, the key fit. Apparently, the monkey who banged up the shaft also did something or other to cause the keyway to wear, and it made it look like it was a size larger than it is. Whatever; as long as it works.

That’s the exciting story of the motor.

It turned out I actually had two VFD’s to choose from. A long time ago, I bought a VFD for my milling machine, thinking I was buying a pulley machine. A machine with multiple drive pulleys allows you to change speeds by moving a belt from one pulley to another. The seller, who tended to screw up a lot, informed me he was sending a variable speed mill instead. Nice, because that’s a pricier tool, and I wasn’t paying extra. But I had already spent maybe $250 for the VFD.

The purpose of the VFD was twofold: 1) to turn 250V 1-phase power into 3-phase power, and 2) to allow me to vary the frequency (changing the motor’s speed) without handling belts. I no longer needed the frequency feature, but I still needed 3-phase, so I hooked the VFD up.

Later on, I bought a big phase converter (machine which turns 1-phase into 3-phase), so I didn’t really need a VFD for the mill. I left the VFD connected anyway, because I was lazy. Yesterday I removed it, and I’ll be connecting the mill to the phase converter soon.

Now I have two VFD’s ready for use. One is small and easy to mount. The other has a nice detachable control pad, so I can mount it out of the way of dust and run an ethernet cable to the control pad. I can connect a remote speed-control pot to the smaller VFD; it won’t be as elegant, but it will work.

I wired the motor up to the VFD. I cut a piece of thick plywood to use as a platform. I put the motor and grinder on the wood, and I clamped them down. I ran the motor with a belt on the grinder and moved things around until I was happy.

After that, I used a stubby pencil and transfer punches to mark drilling locations on the wood, and I made holes for 3/8″ bolts.

The bolts go through the grinder and motor bases and then through the plywood. I didn’t want anything to protrude under the plywood and scrape up my cart, so I used T-nuts. These are nuts that sink into wood. I used a Forstner bit to cut shallow cavities on the underside of the wood (for the T-nut bases to fit into), and then I installed the T-nuts. Perfect.

Drilling wood is a real pain. It always blows out and tears up on the lower side. I made a lot of effort to avoid this. For one thing, I clamped scrap to the underside of the wood so the scrap would support the fibers where the bits came out. For another, I drilled tiny starter holes all the way through the wood, and I used them to guide a spade bit which I applied from the underside. This created shallow 3/8″ holes on the underside. When I drilled down from above, I met these holes, and there was less wood in the way to blow out.

Here’s a photo of what I have now:

Some people insist on metal plates and so on to anchor belt grinders. I guess that’s nice if you work in a factory and you put hundred-pound loads on your grinder rest. The setup I created is as solid as a rock, and it doesn’t have to handle heavy loads. I used 3/4″ plywood, but 1/2″ would have worked fine.

I’m going to sand the rough edges off the platform. Then I think I’ll hit it with truck bed paint. It goes on without primer, it dries fast, it looks good, and it wears like iron. After that, I’ll try to situate rubber feet on the underside of the platform, so they’ll butt up against the inner walls of the cart and hold the platform in place. The platform won’t sit in the cart. It will rest on the outer edges. That lets me use platforms that are larger than the top tray, and it leaves space in the tray for belts and belt grease.

I can retract the tool arm(s) when I’m not using the grinder. That will keep it out of the way, to some extent.

I haven’t figured out what to do about dust. One easy solution is to hang the VFD under the tray, away from dust, and run wires to a pot mounted on the platform. I hate to cut holes in my nice cart, though, and I wonder if it will protect the VFD. Generally, people put them in boxes with air filters. Mine would be exposed, but it would be in an area which sees little dust.

I think that will work. I’ve seen where the dust from grinders falls, and it doesn’t fly around corners or in loops. It falls under the platform and belt. It won’t make it to a VFD under the tray.

I can already tell the grinder is going to be a fantastic tool. While I was setting it up, I used it to remove some of the milling marks from a knife I made. The grinder has a flat platen behind the belt, and you can press flat objects against it, so it creates a flat surface. From the results I got, I believe it will work well enough (accurately enough) to allow me to put flat, scale-free sides on knives.

This will sound crazy, but I held the knife against the platen with my bare fingers, turned the motor on, and let the belt grind it while I held it there. It was no problem at all. In the future, I think I’ll put something between me and the blade, so my fingers won’t hit the belt if I slip, but at low speeds, it’s not likely to hurt me because I can move my hand way in plenty of time.

I’ll need a big contact wheel. That’s is a giant pulley (maybe 10″ in diameter) that replaces the platen. It allows you to grind the sides of knives so they’re slightly hollow. That makes sharpening easier, and it makes for a less clunky knife. Contact wheels cost a lot of money. Not sure why.

I’m going to have two nice grinders, side by side, with speed controls. That will be excellent. If you haven’t used grinders, you don’t understand how useful they are. They sharpen. They deburr. They clean. They shape. They polish. Wonderful machines.

Now I suppose I need to learn about belt grinder safety so I don’t sand myself to death.

Good tools turn frustration into pleasure. I look forward to using this thing.