MetalworkingFun Forum

Been handling too much wood, my hands are clean, and it was too hot today to be working outside so we ventured back into the lonely machine shop.
The 3 jaw for the hardinge was badly bell mouthed so thought we'd tune it up. Tore it apart to clean the scroll and found the back side with the pinions totally dry, not a hint that it ever had lube, HUM. There was a small ding on the end of the mouth that was affecting the fit when I checked with blueing. The other day I repaired that with a bit of scrapping to get a good contact impression.
Set up the tool post grinder and dressed a wheel, which is for a valve seat grinder, have a bunch of them in different sizes, 9/16 course thread bore.


Dave from one of the other forums leant me a set of spacers he'd made to preload the jaws.



After grinding I have between .0005 and .0015 runout, on different sized stock. Not repeatable, clamp the pin and one time you'll get .0005 the next time .0015, pretty much the nature of a 3 jaw, but the dowel pin stays parallel to the bed within .00025 as interpolated off a 1/2 thou test indicator 2 1/2 inches from the chuck.



NOW THE INTERESTING PART.
I've read you should use the pinion marked 0 to get the best results. I do but to be honest have never noticed any difference. I tightened the chuck on the spacers using the 0 one before I ground the jaws. Now if I use the other pinions I get 4 to 5 thou runout on the test pin, never better than 3 and the test pin will be a thou or worse off parallel. Go back to the 0 pinion and all is well. Tomorrows project is to check the 12 inch Bison chuck on the Summit and see if it gives similar results.

I could be wrong but I thought that when you ground the jaws you used a ring that sat on the outside, not the inside - like you would when gripping a section of pipe from the inside. This way, the pressure from grinding is pushing against the ring and not the scroll.

I checked the results on my 3 jaw and found best results when tightening using the #2 pinion. On my friends lathe it is #1.

Think this is the way you want to load them. With the spacers between the jaws your loading it the same way you are when gripping a shaft. I plan to use a ring to hold it when I touch up the outside surfaces.
The Bison on the Summit gets the best results on the first pinion over clockwise from the 0 one, HUM

As I said - I could be wrong

I put a cut across the width of the backing plate on my 3-jaw chuck, inline with the pinion that I got best results with. I then filled the cut with black oil-based paint and wiped off the excess. Makes it easy to spot.

Greg,

Normally when the jaws are worn on a chuck, the scroll is worn as well. Try checking the runout on different diameters of stock and see how much variation you get. Ideally the jaws should be preloaded in the direction of use before grinding them, but as long as the scroll isn't badly worn, it doesn't make much difference. Axial runout is helped the most by grinding, as you have found with your .00025 reading.

Tom

Seams to give 1/2 to 2 thou runout (Clamp once get 1/2 clamp again get 2) from 1/4 to 1 1/2 stock.
Checked the 12 inch 3 jaw Bison on the Summit. The marked pinion gives about 3 thou runout but the next one over clockwise it drops to 1/2 thou on 1 1/2 inch stock.

OK we are happy you are back in the metal shop. Now don't close the doors again until you have your firewood processor finished. That is an order young man!

The only thing I want to hear from you now Greg is, Sir, Yes Sir!

When I bought my Logan it came with a Buck 6 jaw through adjust. The previous owner used a center punch to make a diamond pattern on both the chuck & the OD of the spindle for alignment/mounting. I've stuck with that & am more than pleased with repeat-ability, etc.

BTW, when I was taught how to make soft jaws we used a hardened disk to clamp on with the very back of the jaws and use the same procedure for regrinding 3/6 jaw chucks. This way the clamping pressure is in the same direction as when one would be holding a work piece. If necessary one can relieve the back of the jaws on a surface grinder. This was 40+ years ago and has worked well for me.

Greg,

BTW, that sure looks like a Rockwell/Delta 14" vertical bandsaw in the background.  Does it have the high/low gear box for metal & wood working like mine?

Stan

Thats what I do with the soft jaws too Stan, you clamp down on the spacers Dave lent me, but your doing on the ends of the jaws to remove tipping action.
Was sawing some lumber for a friend of a friend, he said he had a bandsaw his uncle gave him, did I want it. It sounded from his description that it was probably a 14 inch band saw, which I'd been looking for to convert to metal. Couldn't believe when he dropped it off that it had the reduction built in.
Was working in the shop BF but still can't open the big doors to get the processor out. Soon, I promise, Soon.