Hi Nicholas,

You say that the jaws have been assembled sequentially, but are they in the correct slots? Is jaw 1 in slot 1? I would hope that at least one of the slots is numbered. If not I would try moving all the jaws round by one and testing again.

HTH

Rod

As Martin suggests, check for run-out of the chuck mounting surfaces on your threaded adaptor with it fitted in the mill spindle. Any run-out indicated increases the further you move from the measuring point and will be several times greater beyond the chuck jaws.

Emgee

Nicholas,

Self-centering chucks, whether 3 or 4 jaw, have to be assembled in a particular sequence.

First, as already suggested identify the numbered jaws and the numbered slots.

With the chuck on its back on the bench turn the scroll round, observing the number one slot until the outermost end of the scroll appears, then turn it back a little just enough to allow the No 1 jaw to enter the slot and push the jaw down as far as it will go (not very far) then turn the scroll so that it engages the first tooth of the jaw and starts to pull it inwards verifying correct engagement. Turn the scroll until it appears in the No 2 slot and repeat the above with the no 2 jaw and so on with the other two jaws.

This procedure ensures that all the jaws are synchronised with the scroll.

This should solve the problem.

I use a 125mm self centering TOS 4- Jaw chuck in the lathe. Theoretically, a 3 jaw chuck should be better than a 4 jaw for round bar. In my case the 4 jaw TOS has better run out than the 3 Jaw chuck supplied with the lathe, both are more than good enough for a hobby lathe.

Given the 4-jaw will hold square and elliptical stock, I only use the 3-jaw for hex bar now.

So how do I go about setting up chucks?

Aside from stripping and cleaning my process has been.

1. Pop mark a point on the spindle.

2. Fit a backplate, pop mark to align alongside the mark on the spindle

3. Turn the backplate in-situ to reset the register faces for the chuck.

4. Mount the chuck and pop mark to align with the pop mark on the back plate.

This should produce the very best alignment in terms of run out, and everytime you take the chuck off the machine, you can put it back exactly where it came from. Similarly, if you need to strip the chuck, the backplate can always go back exactly where it came from.

Issues – if the backplate is already 'a fit' with the chuck, you have to lose some of the meat out of the backplate, but this has not caused any noticeable problems. For the four jaw, the spigot on the new backplate was a bigger diameter than the chuck register, so perfect for this treatment

Final point – to get best run out keep everything scrupulously clean when assembling chuck to backplate, chuck to lathe, chuck jaws. Any trapped bit of swarf has the ability to throw out the alignment. Same with machined tapers, if the socket isn't clean a bit of detritis gets trapped between the taper and socket, again there is the potential for upsetting the alignment and increasing the run out. Problem is, it tends only to be noticeable when its bad, when it's tiny, it's usually found when the job didn't turn (pardon the pun) out to spec.

Bear in mind I am an expert in these matters – I've nearly finished my third engine… Feedback is a gift

Happy Christmas

Steve

You can tell the jaw order by looking at the back of the jaws. If that is out they will be all over the place. I understand that the zero mark usually indicates the position for jaw one – that jaw is the one that can be pushed in least before it's scrolls meet the scrolls in the chuck itself. Jaw 2 goes in further and so on. The scroll in the chuck needs to be wound round so that it's start is just before the 1st slot then each jaw is inserted in turn while pushing on them and closing the chuck.

Just hope I have the position of the scrolls on the back of the jaws the right way round. I do it without even thinking about it or look at the numbers on them. Where the marks are absent the usual trick is to mark them with a centre punch. One dot for one, 2 for two and so on.

You could try rotating the bar just as the jaws close on it – hard to explain and there is a bit of a knack to it. It needs to be rotated when all of the jaws are touching the bar. It probably will help once you have the technique correct.

John

–

I bought a chinese 3 jaw from a well known dealer , turned out to have a huge run out inspite of certifates with it . Deslaer changed it no problem , second one is fine

Nicholas – first thing is talk to Chronos, let them know that you're experiencing problems. The fact that you've drilled it for a locking bolt isn't going to alter inherent run-out if it's there.

Secondly you need to make sure that your R8 adapter is truly concentric, if it isn't then that's another problem that you should take up with whoever supplied it or made it for you.

Looking at the Chronos site, the backplate of the chuck looks as though it can be fitted in any of 4 orientations, have you tried turning round and checking the run-out to see if it varies, it's possible that when you received it, the backplate was not in the best position, if someone else has done anything to the chuck – why was it so stiff?

The amount of adjustment you're looking for isn't 1.3mm – that's the TIR (total indicated run-out), the eccentricity is half that so you might stand a chance of getting that if the bolt holes have clearance, but I'd expect to find a spigot location between the backplate and the chuck body.

Above all else you need to make sure that all mating surfaces are clean and free of burrs or bruises, they can easily throw the chuck out of line.

Nicholas,

The chuck has two sets of jaws? Have you checked the concentricity using the alternate set of jaws.
This is not the best way to clamp a piece of bar but might indicate to you where the error lies.

Bob D

Sounds like you may be traversing the tool too quickly. How long does it take you to face right across the backplate?

Also,carbide tools don't give their best with shallow cuts. Might be best to get an HSS tool with a small radius on the end and try that.

Neil

Use a HSS tool, at least half the speed, 150 would be better, and it's going to be a slow process. I presume you are holding the tool in the machine vice, and traversing the table. About .25 mm / .010", maybe less is enough of a cut.

Why would you need a 100 mm chuck in a mill? On a rotary table, or dividing head yes, I used my mill to turn a part for my lathe at one time, but unless there was no other way, I would not do it again, I'd just use my Sure Adept.

Ian S C