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Skinner 6” chuck

Jon Paxhia

Plastic
Joined
Oct 4, 2020
I need some help with a skinner 6” lathe chuck, it reads 2-v-6 van Norman-51. I bought a Logan 816, it was a little ruff but the price was right it has 1.5-8 spindle threads. It did not come with the chuck mounted or even the back plate ready. The back plate was Chinese but fit up right and after facing was running .001 out, more then enough for my work. The skinner had roughly .625 mounting holes with a lager counter bore for socket cap screws. I used a .625 transfer punch to mark the holes and drilled and tapped 5/8-11 holes and mounted with 2.25 long bolts. The run out on a piece of work is .035-.040 total swing. I thought the bolts may have been causing a distortion on the chuck since the back plate shoulder is about .001-002 smaller then the chucks. So I drilled 3 new holes to 1/2-13 and tried again. Same results. I have taken the chuck apart and tried to realign the jaws by closing them all the way and making sure there are no gaps, and it seems to stay timed when assembled. Short of grinding the jaws, witch I have no way of doing, and if I did I’d also have to grind the flip side of the jaws since there two piece. Any ideas would be appreciated. Or do I just go buy a new chuck from shars? Can’t afford a bison and such.
 
Yep you got a wore out chuck! A new one of ANY brand will still have some run out. Just the nature of a standard 3 jaw chuck.
 
Well I can accept that, not the news I was hoping for, the chuck is tight as far as I would say, so only option is to grind the jaws?. And a new chuck I would expect to have .005 or less runout not .040. Would you agree?
 
I think it’s a few years newer, as it has 2 piece jaws, what sort of pic/ vid would you like?
 
Well I can accept that, not the news I was hoping for, the chuck is tight as far as I would say, so only option is to grind the jaws?. And a new chuck I would expect to have .005 or less runout not .040. Would you agree?

Well I have bought several Chinese $100-150 6 " Flat back chucks in the last year and both are well under .005. Last one was off Amazon for about a C note shipped. Looking at Mr Pete's video one tooth off on any jaw would sure give a bunch of run out. Way tooo many wear points in that chuck for long term accuracy in my opinion .
 
why is the plate running out 0.001" after facing? what is "total swing" and how straight is the "piece of work"? someting is wrong with 0.04" of runout. take something where you have qualified the straightness and measure in two places. then youll know how it is. next find the tightening sequence that minimises runout.
 
I would guess the plate is .001 out due to old bearings in the head stock. And yes that is total swing. .040 is total swing as well, half of rataiojs is .030 the other is .010. There are only 3 bolts in the chuck total, not sure how to tighten them opposite or in a sequence.
 
Yeah I thinks that’s the way I’m going to go I’m thinking a shars 6” with a back plate is $200 on eBay .
 
Yeah I thinks that’s the way I’m going to go I’m thinking a shars 6” with a back plate is $200 on eBay .

I've only ever had a runout problem with a 3-J twice since 1959.

First was JR HS/HS shop. Problem went away when the two new 4-J's arrived and I mounted them.

Second was at a day job around 1974. Problem went away when the 4-J arrived and I mounted it.

Twice in 61 years?

Almost got bitten a third time when a lathe came in the door with a 3-J on it.

Not as dumb as I look! This time, I already HAD the 4-J's.

:)
 
I would guess the plate is .001 out due to old bearings in the head stock. And yes that is total swing. .040 is total swing as well, half of rataiojs is .030 the other is .010. There are only 3 bolts in the chuck total, not sure how to tighten them opposite or in a sequence.

i was talking about the pinions. or do you only have one? so "total swing" = TIR?
 
Would you do a self centering 4 jaw or independent?

"Self centering" really means "self OFF centering".

Those are every bit as prone to permanently imperfect as a 3-Jaw scroll.

You go and get the ones with fine adjust as well as self-centering, you now have scroll-plate PLUS jackscrews so are still fiddling "some" and have only HALF the grip of a 4-J independent, same as a 3-Jaw scroll only has HALF the grip of a 4-jaw independent.

I'm not so much fussed about imperfect self-centering. Got plenty of collet "systems" if/as/when in a hurry and it actually mattered.

I avoid scroll-operated chucks because I am not amused at having to give-up the extra grip strength!

Only ONE design of scroll I'd trust. Old Skewl British maker, proprietary design. Odd, but effective!

Rare as false teeth for Earthworms, too. More's the pity!

Besides, no need.

Machinists who have never had anything mounted BUT 4-J can center them fast enough and as casually or as carefully as the job requires.

We do NOT all that often split a gnat's eyelash at TIR at all.

Plenty of stock to come off?

Close is good enough, and we start the task with FAR MORE runout than a 3-jaw driver!!!

Because it doesn't actually make a damn, that case!

"Cheating? You can bet your sweet ass it is!

Paychecks came good though!

:D
 








 
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