Daryl's Chuck has RUNOUT!

[DarBee]

Hi All,
I imagine Stu and Ewan will have at least one answer each for me on this one.
Since Stu Ewan and others have given me a bit of 'aggro' over my TPG (if I'm allowed to call it that?) being the angle grinder fitted to the tool post - I have decided that the nay-sayers are right - no where near accurate enough to be 'honestly' useful.

I have also decided that I will persevere but I will make a new spindle for the grinder, fit good quality bearings and extend the arbour section to take a 125 x 12mm grinding wheel. BUT there is a problem with my 3jaw - it's got 0.10mm (0.004") runout. The problem jaw is #3, which is a whisker shorter than the other two.

Is there a 'kosher' method of fixing this runout?

The pic shows the runout and the grinder spindle that will be replaced.

Thanks-in-advance, Daryl

[achjimmy]

Hi All,
I imagine Stu and Ewan will have at least one answer each for me on this one.
Since Stu Ewan and others have given me a bit of 'aggro' over my TPG (if I'm allowed to call it that?) being the angle grinder fitted to the tool post - I have decided that the nay-sayers are right - no where near accurate enough to be 'honestly' useful.

I have also decided that I will persevere but I will make a new spindle for the grinder, fit good quality bearings and extend the arbour section to take a 125 x 12mm grinding wheel. BUT there is a problem with my 3jaw - it's got 0.10mm (0.004") runout. The problem jaw is #3, which is a whisker shorter than the other two.

Is there a 'kosher' method of fixing this runout?

The pic shows the runout and the grinder spindle that will be replaced.

Thanks-in-advance, Daryl

Daryl if youre sure it's the one jaw check it over a few diameters, if it's consistent maybe try polishing a few thou of the othe jaws! But to be honest I never worried to much about run out on small chucks. I just made sure that the backplate spigot had a few thou play and would tap it around to clock it up. That's If it wasn't a Pratt chuck with the eccentric

[Grahame Collins]

I'll state right at the start that I have only heard about , not tied this this one, in discussing chuck run out with a fitter, years ago.

Truing the inner jaws involves the use of a - Yup! you guessed it - Tool Post Grinder.

The jaws are locked into an external ring and the jaws are lightly ground with the said Too Post Grinder. It was a long time ago and I don't remember more details,but then a lathe for me was not on the horizon,so I listened out of being polite rather than interest.

Hopefully that might trigger some memories for those who know much more than me about such repairs.

Grahame who manages without a TPG:D

[Ueee]

Hi Daryl,
What me??? nooooooo:D
For re-chucking accurate work like that i would use a 4 jaw and dial it in.

The process i have heard is the same as what Grahame mentioned. You need to lock the jaws in place and grind them with the TPG.....(not the TPAG:;) But as achjimmy said it could be the scroll, if it is a cheap chuck. You need to test it at different diameters to make sure it is not inaccuracies in the scroll.

Cheers,
Ew

[Stustoys]

Hi Daryl,
What me??? I didnt think so either:D. Maybe I fired one off that missed?

First thing I would try is checking the runout when the chuck is tightened on each of the three sockets. I'm read but have never bother to try that depending on where the error in the chuck is that one socket can be much better than the other two.

Why not a 4 jaw?

The problem I have heard with the external ring is that you are using the other side of the scroll and jaw teeth. I've heard of holding a internal ring at the back of the jaws, grinding, then removing the jaws and grinding the part you couldnt get to.

But regardless of what you do I think a 3 jaw will give you problems unless you can machine everything in one setup and then run out doesnt matter anyway.

Between centers?


Stuart

[PDW]

Is there a 'kosher' method of fixing this runout?


Sure. Learn to use a 4 jaw chuck.

PDW

[Dave J]

I agree with above to use a 4 jaw for this work.

If all you have is a 3 jaw you can machine down the register on the back plate and allow the chuck to move a little as said above.

After doing that place you job in the 3 jaw and run a dial indicator on it and with the chuck bolts only lightly done up and tap it with a soft face hammed to get it to run true, then tighten the bolts and re check the job.

If it's an old chuck or a cheap one it will only run true at this diameter and will need resetting for different diameters, but I find if I set mine it's pretty good at all diameters.

Dave

[DarBee]

OK, thanks all for your info - I think I will try the Dave idea first. Having said that, I do have a forejaw - somewhere??

Of course, I'm sure you all have already guessed that the chuck is a ronable oriental variety.

Regards, Daryl

[RayG]

Hi Daryl,

I wouldn't get too fussed over 4 thou run-out on a 3 jaw chuck. Whatever job you do, you just plan it around so you can do the critical parts with just the one set-up, if you have to remove and re-chuck then just make sure you mark the orientation of the part so it goes back the same way.

Of course if the job absolutely must be swapped around, then use a 4 jaw.

Regards
Ray

[TKO]

The four jaw is of course the answer ,if the work has to be changed around ,and all the forgoing remarks I agree with, but if the four jaw is out of the question I would be testing the part you are going to use and what it shows to be out I would insert a same amount shim under the faulty jaw and retest till acurate,and ajust shim acordingly,and test each time the size of work is changed, I hear what you are all saying, but it is just a short term Idea till the chuck can be reground,that is what I would do if I had to,now if I am wrong for goodness sake put me right.

Eddie

[Combustor]

My chuck was in much the same condition a Daryl's, but I reckoned that with a .004" error there was not much to lose by trying to grind the jaws. I mounted up an electric die grinder with an extended neck then put a metal ring on the outside of the jaws and trued up the outer faces of the jaws before attending to the inside. It's now hardly over .001" error over most of its range, so worth doing, and did not take much time. For a lot of my work, that's close enough. As others say, there is always the 4 jaw, if I have the patience! Combustor. PS, A scrupulous clean of mounting faces before starting is a good idea. I won about .002 there before grinding. (C)

[achjimmy]

Hi Daryl,

The problem I have heard with the external ring is that you are using the other side of the scroll and jaw teeth. I've heard of holding a internal ring at the back of the jaws, grinding, then removing the jaws and grinding the part you couldnt get to.

But regardless of what you do I think a 3 jaw will give you problems unless you can machine everything in one setup and then run out doesnt matter anyway.

Between centers?


Stuart

Stuart is correct you are truing it to the backside of the scroll, in saying that as above it can correct error and get it a lot closer than .004". I think it depends whether it's because of wear or manufacturing tolerance. remembering a three jaw is supposed to be round already machined components and for high precision concentricity use collets.

I was always taught that tool post grinding on a lathe was a big no no. I have done it a few times but always tried to aviod it. Are they worth much? I have a nice Waldon TPG in a case.

[nearnexus]

Are they worth much? I have a nice Waldon TPG in a case.

About $500 - 650 is the current going price for a good one with both spindles.

I have a Waldown C01 and use it a lot. But you have to cover up the lathe well.

Rob

[DarBee]

G'day all,
PDW will be pleased to know that I found my forejaw under the lathe cunningly disguised as a 4-jaw - fitting it up was a PITA, but I haven't lost lost my touch to get better than 0.005mm runout. That will keep me happy for the current job.

But ... I was thinking (yep - very dangerous I know!) of machining a good sized piece of pipe or round stock (about 40mmD), placing that in the 4-jaw, then tightening the 3 jaw onto the machined stock (so it will be up against the 'correct' side of the scroll).

The back of the 3-jaw will then be facing the tool post. I was hoping that the internal register would then just need a (very) light skim to make it concentric with the jaws. I also wondered if it would be any help to re-mount it using loctite bearing mount.

I also like the collect idea as well - I only have a ER32 chuck (in the mini-mill), so while I'm asleep tonight, I will work out how I can mount it into the spindle - considering easy fitment & removal.

Regards, Daryl

[Stustoys]

The back of the 3-jaw will then be facing the tool post. I was hoping that the internal register would then just need a (very) light skim to make it concentric with the jaws. I also wondered if it would be any help to re-mount it using loctite bearing mount.

I also like the collect idea as well - I only have a ER32 chuck (in the mini-mill), so while I'm asleep tonight, I will work out how I can mount it into the spindle - considering easy fitment & removal.
I dont recall what chuck mount you have but I wouldnt be machining the back of the chuck unless I'd checked the runout at several diameters and found it pretty consistent.

Whats the taper in your spindle? you can likely buy an ER32 that will go straight in.


I was always taught that tool post grinding on a lathe was a big no no.
Depends how much you value your lathe. People are hardly likely to be swooning over my lathe in 100 years. Besides that it can always be remachined if I do manage to wear it out.


Stuart

[Dave J]

Check to see if the diameter is running true and the face of the chuck is running true, if they are both true I wouldn't go touching the chuck as the fault will be either the scroll or the jaws.

Dave