Motorized spinning grinding head

[Technical Ted]

Just thought I'd share what I've been up to lately. I designed/built a spinning head for my grinders. One goal was to use materials I had on hand and that lead to some design limitations, but, after multiple design approaches, I came up with a solution.

For the bearings I used a pair of replaced spindle bearings out of a Bridgeport head. These were given to me a while back and although used/replaced they felt and looked fine to me and since I'm only going to be running at probably 350 RPM max and light duty at that I figured they were worth a shot. They are working fine and sure beat spending hundreds of dollars for new ones!

I made the spindle from a piece of B7 bolt material I had on hand which is 4140/42 prehardened (similar to 4140 prehardened). I feel this material will work fine for my use.

Collet wise, although I would have liked 5C, the bearings have too small of a bore for these so I went with my 4C collets. R8 would seem to make sense, but they have no through hole... I'm currently drawing up a 4C mount for a 3" four jaw chuck as well.

After assembly, the bore in the spindle runs within 0.0003" TIR. I'm very happy with this; it could have been a lot worse with all the machining/assembly variables involved. The right thing to do is to grind the spindle bore in on its' own bearings and I may do that, but I'm going to use it for a while and see how things go. My collets, although good brand names, are old/used and don't run perfectly true anyways. I test ground a piece of mild steel and could not detect any out of round condition at all.

The motor is a Parker Hannifin Compumotor stepper and drive. Way over kill for this application, but the only thing I had on hand that was around the right size, power and also has programmable speed control. This made pulley sizing completely irrelevant.

I didn't want to add any additional stresses so instead of welding I used screws and dowel pins for assembly. The only components I had to purchase were oil seals (not to keep oil in since I greased the open bearings, but to keep grinding dust out), the belt (2L V belt) and some fine thread hex head cap screws.

With the threaded top rail and locking flange nut assembly on the rear I left things open to add an 24 position indexing plate and lock pin for indexing, which I'll be designing soon.

Works great!
Ted

 

[Bob Korves]

Very nice job, Ted! If the v-belt causes vibration and/or runout in use, try using an appropriately sized o-ring instead. They run much smoother, and you can always switch back to the v-belt if you are doing a job that requires more torque (most jobs do not.) The o-ring can run in the same pulleys you are using now. O-rings are somewhat safer, too, than v-belts when exposed...

 

[Technical Ted]

Thanks Bob. I was originally thinking the same thing. I ordered a 1/4" round Polyurethane Rubber belt from McMaster Carr. This material is suppose to be more resistant than the black O-ring type belts. The problem was the two oil seals. They fit so tight they added way too much resistance to rotation. I even machined some off the mating surfaces to get the fit I liked, but the belt still slipped some... enough to heat up the pulleys which in turn headed up the spindle. So, I switched to the 2L belt and it worked out beautifully! No vibration, slip or problems whatsoever!

I love McMaster, but sometimes the shipping costs more than the product , which was the case when I had to order the 2L belt. The round belt will go into my parts department!

Thanks,
Ted

 

[mattthemuppet2]

very impressive work!

 

[benmychree]

Typically, precision spindles do not use seals, only laberynth or felt closures that do not drag. My B&S Micromaster uses a multiple O ring drive for the spindle, it is smooth and capable.

 

[derf]

I used a j3 serpentine belt on mine. They have less drag and more traction than a V belt or an O ring.

 

[benmychree]

I had a Leblond cutter grinder years ago, early 1900s, I made a setup to cylindrical grind between centers, made two cone pulleys of steel with 3 steps, radiused in the root diameter and used a leather sewing machine belt to drive it, laced with copper wire. This was in the mid 1970s.

 

[Technical Ted]

Typically, precision spindles do not use seals, only laberynth or felt closures that do not drag. My B&S Micromaster uses a multiple O ring drive for the spindle, it is smooth and capable.

I agree. I originally looked into making something like they use on Bridgeport mills, but felt for a spindle in the horizontal position (vs vertical) and with the fine grinding dust that it would not be adequate. I found some spindle design information on-line from a bearing manufacturer that stated installing oil seals backwards was best when used solely for keeping dirt out, so that is what I did. Now that I have the fit I want on the sealing surfaces and a good belt (2L V belt) it works great! Very smooth, very nice finish and I can't see any out of round condition on my grind. The oil seals should do a great job at keeping the dust out of the bearings and they were an easy/inexpensive thing to use.

Thanks for the suggestions,
Ted

 

[Jubil]

If it performs as good as it looks then you have a winner.
Very nice build.
Chucl

 

[Janderso]

Beautiful build.
I admire your work sir.