3 jaw chuck run out

[oldtiffie]

Softies

Buy/get some jaws for that chuck that "soft jaws" can be fixed/mounted to.

Get/buy/make some soft jaws.

Close the soft jaws onto any bit of round stock that suits and bore and/or face the soft jaws to suit the job in hand.

The machined surfaces in the soft jaws will be as accurate and an as "true" to your lathe as is likely to be required. Should be "true" to within "half a thou" - or better.

Best result for least time, effort, "drama" and buggerising around.

[philbur]

If the chuck is mounted on a backplate remove the chuck from the backplate open the mounting holes on the backplate by 1 mm. Reduce the chuck register diameter by 1 mm. Put the chuck back onto the backplate and your chuck is now adjustable for concentricity.

A common or garden three jaw chuck is a bench vice designed for mounting on a spindle.

Phil

[loose nut]

Even if it was within 1 or 2 thou it wouldn't hold that accuracy for very long anyway, 3 jaws aren't meant to be really accurate at least the ones we can afford.

.003 good
.020 bad
.007 not terrible.

[gnm109]

I clamp a piece of steel round stock with a hole in it.... in the back of the jaws and then use a tool post grinder to true up the jaws. Mark the steel so it aligns with the #1 jaw (or any jaw for that matter as long as you mark it). I then clamp the same piece of steel with the hole in the middle in the newly trued up faces (aligning it with the same jaw) and clean up the back end portion where the piece was clamped to start.

Once done...make sure to dissassemble the chuck and clean it very well. The grinding swarf will chew the chuck to pieces if left inside. Oil it well and then check for true.

Cheers
mac.

That's what I do. I had the jaws of my 6" 3 jaw Enco D1-4 wear loose on the outer ends after some 15 years. I ground it as above and got it very close. I don't remember the number but now the chuck holds nicely.

On a three jaw, some runout is to be expected and really isn't a problem unless you want to machine something round and remove it and replace it. That can cause a problem, but I'm sure everyone here already nows that.

If the jaws aren't loose and the chuck is nice and clean, you can get them quite close with a regrind. I also made a holder for a pneumatic die grinder that I did the job with.

[dm1try]

i recently got a NOS 80mm (3") polish-made BIAL CT-80A chuck. the certificate says:
body runout: 0.01mm (0.0004")
radial runout of a mandrel in inside jaws: 0.01mm (0.0004")
radial runout of a ring in inside jaws outer steps: 0.012mm (0.0005")
radial runout of a ring in outside jaws: 0.012mm (0.0005")
face runout of a ring: 0.006mm (0.00024")
haven't verified that myself yet, though

[darryl]

This just my own experience, but I've found that if you mix the jaws up, they won't even come close to centering. I'm talking about 100 thou or more of offset- if a mounted workpiece has less than 10 thou of runout the jaws are most likely in the right slots.

[polepenhollow]

I have a lathe with an L00 spindle snout.
My chuck had about .015 runout. I took off the chuck, turned the mounting spigot on the backplate undersize by .010.
I held a .625 dia dowel in the chuck jaws and indicated in the dowel/chuck combo to swing "0" on the reduced dia backplate.
Tighten screws and you are in business.
If it goes out in the future or it is radically different at a different dia, re-indicate the part and retighten the chuck to the backplate.
Works great.
KL

[EVguru]

Check if the chuck has a mark by one of the key holes. This is the 'master' and the one that would have been used when the jaws were originally ground. If you decide to grind your jaws then mark one key hole to use.

If you ever need to hold something really tight, you should really use an independant 4 jaw, but using all three key holes will enable you to grip tighter without straining the scroll.

[Black_Moons]

Maybe its not his jaws that are out but just the mounting to the D6-1backplate that isent aligned as theres no register for it to the chuck itself?

[gwilson]

My favorite chuck is the 4 jaw Bison UNIVERSAL chuck. I must have bought 8 of them over the years for a succession of lathes at work and at home.

They all ran only .001" out. I mounted them all on backplates myself. My Bison at home is less than .001" out.

And they weren't too expensive a chuck(at least before their price increases.)

[MichaelP]

Gwilson,

You mean this model allows a self centering (vs. independent) operation with a 0.001" work side runout?

[J Tiers]

Maybe its not his jaws that are out but just the mounting to the D6-1backplate that isent aligned as theres no register for it to the chuck itself?

Easy to check by checking runout on the chuck body. Any decent chuck company will not tolerate much runout of the chuck body vs true axis, it should be in the tenths.