# Motorized spinning grinding head



## Technical Ted (May 20, 2020)

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


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## Bob Korves (May 20, 2020)

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...


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## Technical Ted (May 20, 2020)

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


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## mattthemuppet2 (May 20, 2020)

very impressive work!


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## benmychree (May 20, 2020)

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.


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## derf (May 20, 2020)

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


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## benmychree (May 20, 2020)

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.


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## Technical Ted (May 21, 2020)

benmychree said:


> 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


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## Jubil (May 21, 2020)

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


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## Janderso (May 22, 2020)

Beautiful build.
 I admire your work sir.


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## Technical Ted (Dec 4, 2020)

Now that I've gotten a few other projects done (i.e. refurbishing my new to me Induma milling machine) I decided to design and make the indexing arrangement for my grinding fixture. This first indexing plate I made is for divisions of 2, 3, 4 and 6 which will be the most common for my use. I can make up additional plates if/when needed. I basically copied the design of a smaller grinding jig I got with my tool and cutter grinder that was pretty well worn. So now all I have to do it remove the motor and install the locking pin arrangement and I'm ready to go!

Ted


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## Technical Ted (Dec 19, 2020)

Finished up the last piece of the puzzle... a 3" 4 jaw chuck for the head. I didn't want a 3 jaw, because I wanted something I could dial in exact and a 3 jaw of that quality would have been way to expensive for my budget. Also, for small diameter stuff, I have Jacobs chucks mounted on straight arbors I can hold in a collet. 

It sure was handy having a lathe that used 4C collets to make it!

Ted


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## Janderso (Dec 20, 2020)

I don’t know how I missed this post back in May.
Very impressive work sir!!
Wow


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## Technical Ted (Dec 20, 2020)

Janderso said:


> I don’t know how I missed this post back in May.
> Very impressive work sir!!
> Wow



Thanks!

Ted


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