Pulley Nearly Finished

I guess everyone is wondering how to make a crowned pulley for a belt grinder.

I am still mired in the belt grinder project. I’m sort of thinking my best bet is a 3HP 2-pole motor, but I have a 2HP 4-pole motor sitting around, and I want to test it to see how well it works. Maybe it’s the answer.

I tried the 3HP motor at 167 Hz (5000 feet per minute on the belt), and the VFD couldn’t deal with it. I know for a fact it can run the 2HP motor that fast.

It’s too bad I don’t know much about electrical motors. I sort of suspect that the people who have been giving me advice don’t know much either. Some have told me that when you double the speed of a motor, you halve the torque. I have no idea whether that’s true or not. It’s not that easy to find information on 3-phase motors online. I am planning to try to educate myself, but I haven’t succeeded yet.

I had a drive pulley which fit the 2HP motor, but I bored it out to fit the 3HP motor, so I can’t use it on the small motor. That meant I had to make a new drive wheel. Simple, right? Turn a 4″-thick pulley on the lathe, bore a hole, add a set screw…done. Actually, that would probably work, but I wanted to be totally certain the belt would track correctly, so I made a crowned wheel. I finished it a few minutes ago. But for the set screw hole, it’s done.

I have read that you only need one crowned wheel on a machine to make the belt track, but everyone seems to use crowned drive pulleys as well as crowned tracking pulleys, so I don’t want to rock the boat just yet.

Making the pulley was a bit of a pain. In case someone Googles the process in the future, I will leave some information.

First of all, as I said above, you may be wasting your time. You may be able to use a cylindrical pulley. Check it out, if you can.

Once you decide to make a crowned pulley, you need to know a couple of things. The crown doesn’t need to go all the way to the center of the wheel. You can just crown it toward the outside. How far toward the outside? I don’t know.

Also, for a 2″-wide belt, you want about 0.030″ of crowning. That’s radius, not diameter. Sadly, I didn’t pay attention, and I took 0.030″ off the diameter. I forgot that my lathe reads diameter measurements, not radial ones. I’m sure it will still work, though, since there is a ton of slack in the suggested measurements.

I did not have 4″ round aluminum stock lying around, so I used 4″ square stock. That was fun. I had to cut 3.5″ off on the band saw, and then I had to put it in the 4-jaw chuck. I turned part of it down to a 4″ cylinder (slightly smaller due to inevitable chucking error). Then I drilled a hole deep enough for the motor shaft. After that, I crowned one end.

The crowning job was simple. I set the compound slide to around 1/2 a degree, so it would come toward me very slowly as I moved the tool toward the headstock. With this setup, I could start the crowning cut 0.030″ into the work, and it would back out completely as I cut about an inch toward the headstock. This worked perfectly; I had a cylinder with one end that was very slightly tapered.

Then I made my mistake. I parted the cylinder off of the square bit.

I should have crowned the other end at that point, because it was firmly chucked, and everything was completely concentric with the lathe’s axis. Oh, well.

Because I now had a cylinder with one cruddy-looking, parted-off end, and it wasn’t chucked, I had some extra work to do.

First, I chucked it, used a dial indicator to get it concentric, and faced the rough end. I knew this was the best grip I would ever have on the part, so I took this opportunity to bore the hole to size. I opened it to 5/8″ with an S&D bit, and then I finished it up with a boring bar.

It’s frustrating, boring things to size when you can’t test fit them. The motor could not be lifted onto the lathe, and I could not take the part out of the chuck without messing things up. I had to run between the lathe and motor with dial calipers, which are not all that accurate. When it was all said and done, I was still a thousandth or two over the size of the shaft. A totally snug fit would have been nicer, but what I got was perfectly acceptable.

When that was done, I had to shove the part way out in the chuck’s jaws, with the tapered side toward the headstock. That means the chuck was gripping a tapered part. Usually, this is a really bad idea, because chuck jaws are very straight. If a part is smaller toward the headstock end, the jaws will only grip farther toward the tailstock, and if you don’t get a good grip, the part can move or even fall out. But the taper on my part was very small, I am brave, and I am too lazy to make an arbor or take other extraordinary measures to get it perfect.

I managed to put a taper on the exposed end, and then I rested a straightedge on the wheel and rocked it to see where the crown’s apex was. It was a bit off center, so I used emery cloth to sand the wheel until there was no pointy apex and the crowning appeared symmetrical.

Great.

With all that done, I had to put a 3/16″ keyway in the wheel.

Keyways are tight slots made with broaches. A broach is sort of like a really thick saw blade that only cuts in one direction. You use a special bushing to hold it in the wheel, and you push it with a press.

In Youtube videos, this is really easy. People use crummy, small Chinese arbor presses and broach things in no time. That didn’t work for me. It will work with a thin wheel, but the thicker a wheel is, the more pressure you need. Earlier this week, I broached a 1/4″ keyway, and I had to use a 20-ton press. Today I broached a 3/16″ keyway, which should be easier, and my 3-ton arbor press was just barely enough.

I learned something disturbing: broaches aren’t made for fat wheels. If a wheel is too thick, a broach will not be finished cutting when you push it until the end is flush with the top of the wheel. I had to put a punch on top of the broach and push it the rest of the way through. On top of that, I had to broach it from both sides. Very aggravating. A 1/4″ broach is maybe 1.5 times as long as a 3/16″ broach, so the smaller your keyway is, the more likely you are to get stuck.

I finally got it done, and now I have a beautiful wheel that needs a set screw hole. Once that’s done, I’ll throw it on the little motor and fire it up.

I suspect this wheel is actually better than the one I bought, and having made it myself, I can see how hard it is to make one with accurate dimensions.

I still have the little motor the Post Office broke. The seller filed a claim, and they paid it. He didn’t want the motor back. The Post Office didn’t ask for it. Now it’s here, with one broken bolt hole. I managed to get the fan working, so the motor can be used. I’m almost afraid that if I turn it on, the Post Office Fraud Squad will swoop in and arrest me.

I don’t know what to say about that. They did screw up the motor, and it was non-functional. It’s still seriously damaged, so I didn’t get what I paid for. But I feel weird, sitting here with a working motor I didn’t pay for.

I guess all parties are happy, so let the good times roll. And even if it works, I plan to replace it, because the broken base is depressing to look it.

The information I have received about motors and speeds and VFD’s has been inconsistent and tinged with ignorance, so I’m still going by trial and error. Anyway, I should be up and grinding tonight, and then I’ll have more data.

I’m excited that I can make crowned pulleys. I’m even more excited to know that I probably don’t have to.

Some day, possibly years from now, I will post a photo of a finished knife I made.

That’s all I have. You can stop pretending to be interested now.