Bantam lathe chuck

That's a huge amount of runout. Did it just start doing this, or was it like it before? Have you tried putting the jaws in different slots? Are the jaws and slots numbered at all?

Or it may be the jaws are bellmouthed and giving an exaggerated runout. Can be checked by visual inspection while tightening jaws on to a piece of ground bar or silver steel etc. It may be possible to regrind the chuck jaws - or fit new ones if you can get them - if bellmouthing is the problem. See recent article in MEW for how to do it.

If the problem however is the scroll plate distorted, you will need a new one of them too, by which time a new chuck is looking better and better.

Trouble with a bigger chuck could be extra load on the headstock bearings. Best to check with Colchester's recommendations on that one.

I've got a larger (160mm HBM brand) chuck on mine. Not sure what possible issue you could expect to result from fitting a larger chuck. The increase you suggest would approximately double the weight but the machining forces the spindle is designed for are much in excess of this.

The main limitation with a larger diameter chuck would be the jaws clashing with the carriage but I can tell you that isn't an issue. Even with the jaws near maximum stickout, you have clearance left over and the additional capacity is worth any extra cost. With runout like that, you can only benefit from a new chuck, even a Xmas cracker one!

Murray

Hello Ian,

Before you spend any money, my bet is on the fact you have the jaws mixed up in the slots. I am assuming the chuck ran true before you took it to pieces

#1 usually has the least amount of scroll engagement on the first 'tooth' into the scroll, #2 progressively more and most with jaw #3. Are the jaw slots numbered and for that matter the jaws themselves?

If the jaws are not numbered and you stand the jaws on a plate on the gripping surfaces, you will see the progressive effects I mention. Number them 1 to 3 accordingly

If the chuck jaws are not numbered either, then assemble the chuck with your newly marked jaw #1 into a slot so that it just clicks into the scroll as you wind it anticlockwise when looking at the face of the chuck. Then wind the scroll clockwise until the start of the scroll just shows in the next slot round [also clockwise] Engage the jaw as I described and do the operation again for the final jaw.

Now test the chuck for run out, note the value and take all the jaws out again and repeat the whole sequence starting this time from the next jaw slot round in a clockwise direction. Test again for run out, note the result and repeat the whole thing again for the final slot. You will then have three set of run out readings.

Pick the best and build the chuck up accordingly, but this time mark positions permanently in some way. It is a lot of work but the only way to get it right in the absence of any helpful jaw and slot markings

Regards

Brian

Hmm. As the scroll itself has only one "start", the 3 jaws are each quite distinctly different and if you got them mixed up (wrong order), you'd see considerably more than 0.3mm - more like a couple of mm. If they are indeed fitted in the correct sequence but in the wrong starting slot, then I'd be surprised to see that amount of runout.

Time for a new chuck - you shouldn't require any further excuse!

Murray

Edited By Muzzer on 21/07/2018 15:24:11

The jaws could simply be in the wrong slots, eg 1 in 2 slot, 2 in 3 slot, 3 in 1 slot. They would then look right and meet properly, but not as set up when the jaw inner face was ground.

And in my experience, wear and damage are at least as likely on the scroll, as on the jaws. And on some small chucks, the solid-looking housing may have suffered, too. This might be the result, for example, of a parting-off disaster, or a serious dig-in turning brass.

Cheers, Tim

I’m with Tim. I had an unmarked chuck and jaws with different numbers stamped on them (not the 1, 2 and 3). Run out is very acceptable, as long as I start in the right slot. Chuck is now dot punched adjacent to the correct slot. This reminds me - I have never checked the other set of jaws for runout...

Almost there but can have a serious inbalance even if the jaws are in the correct positions/slots when you dont start at number 1.

Assuming you know which jaw goes in to which slot, all mine are hard marked by factory, soft jaws marked 1,2 or 3. In the chuck theres usually a marking 1 2 or 3.
At one time i probably removed jaws 8 times a day, takes about 3 mins.

Best way put all jaws in correct slots and push in.
Scroll anti clockwise until Number 1 drops down, keep pressure on all 3 jaws by pushing in whilst scrolling this time clockwise.
Check is wind in see if jaws meet equal.

If find theres runout now swap the jaws around and hard mark the things and the chuck wont go wrong its real easy.

I bought a lathe (also a Bantam, ironically) which had a Pratt Burnerd chuck that produced variable runout in the part between about 8 and 15 thou. The jaws were a good fit in the slots, didn't appear worn and there was nothing obviously 'wrong' with the chuck except that it had runout.

Turned out that the chuck was slightly bell-mouthed. Gently holding a part in the jaws meant that you could rock it around as it was only held on the very back of the jaws. The jaws were perfect, it was the body of the chuck that was deformed. This was a 4-1/2 inch Pratt Burnerd integral camlock chuck so a good quality item, I guess that sometime in the past someone must have really wrenched down on a part held at the end of the jaws or maybe had some other even where the part was torn out, permanently damaging the chuck body..

Soon after I bought a tidy 5" PB chuck that only had outside jaws so I tried the jaws from the bent 4-1/2" chuck in the 5" one and they consistently gave better than 3 thou runout on both the inside and outside sets.

The main point of the story is that it's common to immediately suspect worn jaws or a worn scroll and often the attempted 'cure' is to grind the jaws but don't jump to this conclusion too quickly - hardened steel jaws are tough and slow to wear, iron chuck bodies not so much so do your investigations before grinding parts that might have nothing wrong with them.

Back from shopping trip and back to workshop. Stripped and cleaned the chuck again. Assembled and refitted to lathe. Clocked chuck body again with negligible run out . Fitted a straight to MT3 adapter into the chuck and set the clock gauge up. Rotated the chuck CW and CCW to get the worst run out, around 90 degrees in each direction. Also tried same tests with a test bar I have and got similar results. I can't remember checking this before so its probably been like this since I got the lathe and I haven't really done much on it until now. Rotagrip have a discount on chucks at the moment so that might be an option but they are still expensive.

Have you thought about grinding the chuck jaws in situ, if they are bell mouthed?

That ought to take out any bell mouthing or slop between jaws and scroll plate.

Unless, heaven forbid, the chuck IS a basket case.

Any chance of being able to carry out any checks with the other set of jaws? That ought to show whether the problem is with the jaws or the scroll or chuck body.

Howard

From the pictures above it looks as though you are measuring runout some four to six inches out from the chuck. This will exaggerate the runout of the chuck by a serious factor. Measurements should be on the cylinder as close to the chuck jaws as you can get. At that point, if runout is within a couple of thou, that is as good as you are likely to get on a used chuck. If you can get it within a thou you are doing well.

It may well be that you have the usual small bit of bellmouthing of the old chuck, exaggerated by the distance out to the dial indicator. It may or may not be worth grinding the jaws (See recent article in MEW for that process.) depending on how bad it is up next to the jaws.

Hopper has a good point. Also, although the MT adaptor may be parallel on the outside, it is made for being ‘parallel’ on the inner surface. If of cheap Chinese origin, it could be anything!

Pull the jaws out of the chuck. Set the chuck so that one jaw slot is perfectly horizontal (at the back or the front) and run a tenth-reading DTI along the jaw guide (with the mag mount set on the cross slide). If the dial reading goes up or down rotate the chuck 180 degrees so the slot is now pointing the opposite way and repeat the test using the slide on the same range of travel i.e. don't wind the cross-slide to the other end, re-position the mag mount.

If you get anything but the same reading with the jaw slot at the front and the rear, your chuck is fubar.

Managed to get some time in the shop this afternoon and got the test bar back in the chuck. At 10mm from the front of the jaws I'm still getting from 0.17CW to 0.11CCW. Pete I will give that a try tomorrow. On a good note I received a set of 3d printed rail cleaners that I got from the bay and they fit nicely. I was also part way through a cnc router rebuild and decide not to go any further with it so when I get the various bits and pieces sold on I can get myself a nice new shiny chuck.

Bit of an update on this. I decided to get a new chuck and went for a P&B 160mm one. Anyway chuck arrived and has been cleaned and fitted. Test bar back in the chuck with great results. I went for a bigger chuck not so that I can turn really big parts but I can now get 45mm in through the chuck body.

I've heard of woodworm, but what's been at your cross slide?

But all's well that ends well! Now you really start to enjoy yourself!

Howard

Well sorted Ian, any links to the chuck that you bought in case others need to go down the same route?

Howard it was like that when I got it. I presume its previous owner had some other kit attached at some point. The link to the 160mm P&B chuck is http://www.rotagriponline.com/index.php?page=shop.product_details&flypage=flypage-ask.tpl&product_id=3534&category_id=234&option=com_virtuemart&Itemid=29

The cross slides came predrilled / tapped for a variety of tool posts and accessories (plus the gib fixing bolts) but even so, that one seems to have received some "additional attention"!

Good to see the problem has been fixed. This illustrates the essential requirement to possess a wide variety of chucks (and indeed other accessories). If you don't have several "known good" chucks, you can't narrow down any issues so easily. That's the logic anyway!

Murray