Thread: Is there a chuck doctor in the house?

Dear members,

I recently purchased a new 65mm 3-jaw, self centering, scroll type chuck for my mini lathe, and to my surprise, it did not run true.

I tried to take a lick off the inside faces of the jaws, but that did not make much difference.
I ground the jaws in situ with my Dremel set up as a tool post grinder, and with the chuck spinning at about 2000 RPM. I'm afraid to keep on grinding, I need to hold fine work.

My question is, who can I take the chuck to for professional grinding?

I live in the Northern suburbs of Melbourne.

Hope someone can help.

Regards,

Ken

Pretty much anyone with a surface grinder and a cylindrical grinder capable of doing internal work could do it, mate.

Whack the jaws up on the surface grinder and re-do the angles & notches if necessary to allow fine diameters to be held, then put it up on the cylindrical and grind the jaws true.

Not a hard job, just time consuming. (Which will be costly if done at shop prices.)

If it's brand spankers, you can't get it swapped for another fresh one?

Gentlemen,

I am surprised I have had only one reply to my plea.

This problem must come up often. My chuck screws directly onto the lathe spindle, so I am tempted to make up an adaptor plate/back plate. By this I mean screw a back plate onto the spindle, then mount the chuck to the back plate via an adaptor, with some form of adjustment to correct misaligment.

Any further comments would be appreciated.

Regards,

Ken

G'day Ken.
I had a similar problem with the 3 jaw chuck.
I chucked it and now run a 4 jaw chuck all the time.
I bought a good Starret dial gauge and now have no problems.
Setup time is a bit longer, but well worth it.

Is it the whole chuck misaligned or is it just the jaws? Is it worth posting some pics of the problem?

is it the jaws not running true or the chuck?

did you purchase your chuck in australia,if so why didnt you take it back.

Have the jaws been removed my point being with a three jaw chuck each jaw should be numbered and only fit in that numbered slot and incerted into the chuck in order 1...tighten the chuck slightly 2...tighten the chuck slightly 3...mix them up and you have problems
Thus the question is there numbers marked on the chuck and jaws have a VERY close look remove them all and re engage in order 1...2...3...

Rgds

Originally Posted by neksmerj

Gentlemen,

I am surprised I have had only one reply to my plea.

This problem must come up often. My chuck screws directly onto the lathe spindle, so I am tempted to make up an adaptor plate/back plate. By this I mean screw a back plate onto the spindle, then mount the chuck to the back plate via an adaptor, with some form of adjustment to correct misaligment.

Any further comments would be appreciated.

Regards,

Ken

If you go the backing plate way check out this link ,gives step by step instructions how to do it.
http://www.metalwebnews.com/howto/ch.../chuckmnt.html

It will depend if your chuck has recess in the rear face to locate on the backing plate and tapped holes to bolt it on.
Once you get the chuck running true then you can mess with the jaws.

With the greatest respect, jaw No.1 is in slot No.1, jaw 2 is in slot No.2, and jaw No.3 is in slot No.3.

Even with my failing eyesight, 1 is 1, 2 is 2, and 3 is 3.

The chuck is very small at 65mm in dia, and is basically a flat disk with 3 jaws, tightened by tommy bars. It's not like a conventional chuck with a Tee handle chuck key.

It was purchased from the UK. Where it was made was probably from a non English speaking country.

It does not have a recess in the back, hence the need for an adaptor to attach it to a backing plate.

The body of the chuck runs true, the jaws do not.

Further comments are welcome, but please, I am a novice, not a dill.

Ken

Hi

If you need to hold fine work and hold it accurately, then your first mistake is buying a THREE jaw chuck.

ALL three jaw chucks have some runout. Even if you correct the runout on YOUR lathe, there is no guarantee that it will again run true when you open and close the chuck jaws.

This is a fact of life and we live with that. You can be sure that (everything else being ok) the item you turn in the three jaw chuck will be concentric to the current mounting in the chuck.

Theoretically you should be able to remove the chuck with the item in the jaws and remount the chuck on the lathe and it should run true. All this of course requires best practices to be in use, clean spindle threads and clean three jaw chuck etc.

If you need to do much fine work and have repeatability then you need to consider a collet based method of work holding.

MrFixIt,

I'm inclined to agree with you, none of the 3 jaw chucks I have, run true.

I reckon you are right by suggesting a collet based system. Seams like I will have to make up something, as I'm pretty sure there won't be anything around for the Unimat 3 mini lathe. If there is, a set would be worth more than two gold bars!

Most of my hobby work is small, ranging in size from 3mm to 10mm round, so, has anyone made up their own set of collets? If so, any drawings to get me started?

Thanks for your comments.

Ken

if you are thinking of trying to make an offset adaptor plate to compensate for your jaw runout good luck.The only way i can think you may be able to achieve this is by mounting a 4 jaw chuck,placing a bit of ground stock as large as can be held by 4 and 3 jaw chuck,put the bar in 4 jaw then open 3 jaw and also put on stock,machine recess in back of 3 jaw ,maybe 60 od by 2-3 deep if possible,IVE LEFT A BIT OF DETAIL OUT SO BEAR WITH ME. before mounting the ground bar in 4 jaw rough out your mounting plate,if you can weld weld a spigot to the centre of your mounting plate use a bit bright a suitable dia to tap for mounting to spindle,i would probably use a bit of 65od black bar 10 -12 mm thick,machine this all over after welding spigot on,dont drill it,finish turn od of the mounting plate to a suitable od for your chuck,and mark a pcd on the face while in chuck at suitable dia,NOW GO BACK TO THE 2 CHUCKSmachine the back of your 3 jaw to suit the mounting plate with appropriate clearence,remove 3 jaw from lathe ,mark holes on backing plate drill your tapping drill size and spot through for chuck,remove the plate drill and tap chuck,drill clearance holes for backing plate,fit backing plate to chuck put chuck back on spindle turn od of spigot and drill and tap or turn thread to suit your spindle,this should now have your chuck running out but your jaws running true.(maybe)

Buy yourself a set of drop in collets that use a draw bar. Make a sleeve to fit spindle at either end. Be warned. Collets age like anything else and don't hold their accuracy their entire life, especially if over-tightened regularly. Also note that most collets will only run true to about a thou or so. (And that's fresh out of the box.)

Hum, not trying to be disrespectful guys but how much does a good chuck cost, one that runs true that is? Is it worth to do all that work?
I have two chucks kicking around on the floor of my shed, one is 4 jaw the other is 3 and I use them for door stoppers....

Are this any good?
chuck
more chuck

This is fairly cheap!
Old Chuck