Thread: Hercus chuck problem I think

I suggest you do a search on 'chuck runout', to save us typing the same stuff all over again.
FWIW, here is the short version:

1. 'Self centering' is a lie, at least for scroll chucks.
2. Buy a 4 jaw independent chuck and learn how to use it. It's a rite of passage.
3. Most likely your chucks can be improved somewhat by careful attention to mounting.

Thanks Bryan
Imm should of mentioned I have a four jaw chuck
So has you say maybe it's time I stopped being shy off the four jaw and get on with it

Originally Posted by Simplicity

There's paint there on the register surface of the spindle nose just near the tip of the dial gauge - not where you want paint.
Probably best to remove it, ditto for any paint on the vertical face of the spindle nose where the chucks make contact when tightened, as well as any paint in the nose threads. Depending on paint thickness, removal may improve the concentricity of work holding.

Other than that, give the 4-jaw a run as advised.

Cheers,
Bill

Thanks Bill
Will get the paint off
And see how that goes I didn't think the chuck round all the way up to there but it won't take much either to eliminate the paint either and eliminate that possible cause

And just checked I'm wrong the the chuck does run all the way past the paint ( lol

Originally Posted by Simplicity

Thanks Bill
Will get the paint off
And see how that goes I didn't think the chuck round all the way up to there but it won't take much either to eliminate the paint either and eliminate that possible cause

The first issue with the paint is that it invalidates the DTI reading for spindle run out because you are adding the uneven paint thickness to the spindle diameter and measuring both. Admittedly, the run out reading result appears to be a fair guess at the paint film thickness, so there may be even less run out than the initial reading suggests.

There definitely is paint in one patch of the thread, and maybe a patch on the register face of the spindle. The chuck backplate and spindle thread are like any nut and bolt, there has to be some clearance between the threads or you cannot move one relative to the other. Looking at some of the cheaper (Chinese) nuts and bolts you find in hardware shops and barns, the nuts are very loose on the bolt and have a lot of lateral movement. Hopefully the thread on the spindle and backplate have been formed with a lot more precision, but they still need some clearance.

The cheapo nuts and bolts work reasonably effectively, provided that you don't strip the thread, once tightened. This is because the underside of the bolt head and the underside of the nut make intimate contact with the material they are sandwiching, and align to those surfaces and eliminate the lateral movement present in the loosely coupled situation. The same happens with the spindle nose thread and backplate, the tread provides the coupling forces to fix the chuck, but the register faces on the spindle and backplate provide the precision alignment you need to make the chuck reasonably accurate. A patch of paint on the register will cock the chuck to one side and throw everything (including the four jaw) out of whack.

Ok I've cleaned all the paint of carefully soften it with turbs first.
Then just rubbed polished it off with some cloth.
Didn't want to scratch it all up
Then did my first test again same results in my view being a novice it's not the spindle.
I'm pretty sure it's the chucks.
They may and I'm speculating here.
That the chucks had a hard life before coming into my hands
The lathe is 9inch Hercus model AR
And was brought by my father in law (ex machinest)
From box hill tafe just before he left there in the 80s I think.
Unfortunately now the father in law is getting quite old
So can't really ask him for help ?

Hi Just a few observations from me , a novice .

Your 2nd test . The bar your have in the chuck is sitting in the outer edges of the jaws , this isn't an ideal method for testing the runout of that chuck .

How old is that chuck ? Grab the jaws and try to wobble them from side to side , get a feel of the wear in the jaw guides . There should not be ANY sideways movement of the jaws at all .

BTW a half decent 3 jaw chuck should have around a .003" runout .. Mike

- A brand new, good quality brand name 3-jaw chuck of 125mm diameter in the $500 price class has less than 0.025mm runout. But note that this accuracy can very quickly and permanently be destroyed by abusing the chuck, such as overtightening or using a hammer on the workpiece etc.

- A less expensive chuck in the $300 price class has when new typically 0.06 to 0.1mm runout. This too can quickly be degraded substantially if abused. Lowest cost Chinese and India made chucks have been knows to be off as much as 0.5mm from new.


Please download this .pdf file. Go to page 4. Here you see how the 6 (six) runouts that a chuck can have are measured to DIN standard. It is important that everyone measures chuck runouts the same way (eg same distance from the jaws etc) for the results to be truly comparable.
http://www.tos.cz/tospdf/technicke_informace.pdf

This website gives you the same figures in inches, if you do not like using metric measurements:
http://www.jtsmach.com/jtswebshop/Workholding/LC035.asp

Now you have a good idea what to expect from new, or well looked after used chuck.

Your chuck is not new. The scroll may be worn in places. The jaws may not anymore be a tight fit in the chuck body slots. The Jaw's clamping surfaces may have been damaged and worn by clamping onto the irregular hard outside scale of warm rolled steel. Someone may have used a mallet to straighten bar stock clamped in the chuck. Also, the fact that there is paint on the registration flange of your spindle nose, means that the chuck backplate is not a tight fit to the registration flange, and chuck centering depends entirely on the spindle thread. Chucks do not last forever. If you like to use the 3-jaw chuck a lot, and you expect it to repeat reliably to better than 0.1mm, it is maybe time to consider a new chuck. Chris

Ok I'm starting to think
I buy a new expensive 3 jaw
Learn to use my 4 jaw
Find a good second hand 3 jaw
Or just put up with what I have
Thanks for all the great replys
I feel I'm a little bit further a long this road now ) lol

Originally Posted by Simplicity

Ok I'm starting to think
I buy a new expensive 3 jaw

Not worth it because the most expensive 3 jaws have runout... Is in inherent to the design.... I use my 3 jaw much more then the 4 jaw..

You just work around it.... I did fit a new $100 chinese chuck to my Hercus though...

If you get a new chuck, you will need a new backplate as well and machine it to size... The backplate is the adapter that screws onto the spindle nose and bolts onto the back of the chuck.

Have a read through this thread..... with some of my experiences there https://www.woodworkforums.com/showth...31#post1427131

I've never really measured the run out on my 3 jaw. I'm thinking it would not impress me! I just work around it, if I need a 50mm finished piece then I start with 52mm! I have never really seen it as a limitation. It is as good as the lathe it is attached to which is all good enough for my use.


Simon

Looking at the picture, the jaws of the chuck appear to be replaceable soft jaws. Can you make an impression on them with a file? If so they could be a part of your problem. Do you have any other chuck jaws with matching numbers to the chuck?
Mm.

As said earlier the length of material you are using to check is a bit short.

A longer piece passing through the chuck to at least reach the rear of your jaws would give a better reading.

As said the jaws may be worn on the outer edge giving a possible false indication.

If after checking again you have a similar result then there may be something wrong with the jaws or chuck.

Have you removed the jaws from the chuck.

If so have you replaced the jaws into the same position they came from,they should be numbered to correspond with the chuck.

If this is all good, reverse the jaws and do a similar test.

This should indicate if the outside jaw is worn/faulty or if there may be a problem with the chuck.