rescuing a chuck

While looking for something (which, needless to say I didn't find!) I came across a used 4" Burnerd 4-jaw SC chuck which I had forgotten about. It was a show or autojumble purchase in the distant past, and I had presumably been impressed by the fact that it had both sets of jaws. I started to check it out, and changed from the outside jaws, which were in place when I bought it, to the inside jaws and was puzzled to find that they did not meet in the centre. After several attempts I finally persuaded myself that I had not made a mistake inserting them, looked at the teeth and realised that there was a problem! (upper panel in the picture). Obviously these are the set which I would most often need. The cost of new replacements would be rediculous, and the chance of finding a used set of four is in the hen's teeth category. Could I grind off the undamaged first tooth on jaws 2 and 3 and the damaged tooth on jaw 4 and just put up with the resulting loss in maximum capacity? The scroll appears to be OK. The good set are in the lower panel for comparison

It was definitely a case of caveat emptor - I should have been alerted by the tool marks on the face of the body and the fact that the outside jaws were installed, which are much less likely to be used routinely.

If you insert each the broken jaws one revolution of the scroll "late", It should work I would hope. Not as robust though and a bit of a faff.

Niall exactly right, grind off the tooth on jaw 2 and the remains of the one on jaw 4 also make sure there is no remnants of the broken off jaws on 1 & 3 it should then work OK but as you are aware with reduced capacity.

No looked but try Rotagrip for spare jaws.

John

Why are you talking about reduced capacity? you surely do not intend to use the jaws with only the last partial tooth gripping the scroll.

Thanks for the comments. I'll try surgery!

Bayzle, yes indeed. It will be used on a Myford so with small bar only!

Alternatively you can try reordering the fitting sequence so that from your photo jaws in number sequence go into the chuck in order sequence of:-

Jaw No 1 2 3 4

Seq No 3 1 4 2

I have a similar problem with one of my chucks and have found this works well!

Insert number 2, then 4, then 1, then 3. Each in their proper positions, not sequentially. That should do the trick without making two of the jaws weaker.

Edited By not done it yet on 06/06/2020 13:32:34

Jaws do come up for sale frequently on ebay, but you have to be careful that they are the same size as yours. We had two PB 4" chucks with the same type of damage and I found that the jaws were not interchangeable. It is always the same teeth broken by ham fisted people who must fit work that is too big for the chuck. There is a possibility that these might be suitable:

https://www.ebay.co.uk/itm/Lathe-3-Jaw-Scroll-Chuck-Jaws-Very-Good-Condition-Hard-Internal/133429444822?hash=item1f1103c0d6:g:RHcAAOSwb7te2MHg

Edited By old mart on 06/06/2020 14:17:27

He needs 4, unless he mixes jaws with different numbers?

Thanks NDIY and Oily Rag

Yes, reordering the sequence works fine and will make the chuck usable for now. I suspect it may no longer be very precise, but I'll strip and clean it and see. Anyway, it's useful to have for quick and dirty jobs. I'll keep my eyes out for a replacement set, but in my experience even a set which is nominally correct can need some fettling to work smoothly. Sets of four are rare.

I think bodging the jaws of this poor chuck may be counter-productive. Maybe the scroll is mutilated as well. That jaw damage was done by a poor operator. Chances are he persistently overtightened the chuck, and maybe being a gorilla he abused it in other ways. Assess the chuck carefully throughout. It might be Beyond Economic Repair, a time wasting money pit. A Bernerd chuck in good condition is worth having, but a Bernerd chuck in poor condition is junk.

Alternatively, if the Bernerd is in good nick, hurrah, is loading mangled jaws into it respectable? My feeling is chaps proud of owning quality tools should cough up cheerfully when spares are needed. Otherwise, there's grave danger of believing one has good tools when they've been spoiled by cost-cutting maintenance. In this example, holding strength of the jaws is reduced, and pressure will be put on teeth that look OK, but could be strained, and the operating range is reduced. Good tools should be fixed properly. Buy new jaws!

Just an opinion, it's not my money I'm spending. Feel free to disagree.

Dave

It will be just as precise but just not for use at the largest normal chuck opening, that is all. Being a PB 4 jaw self-centring chuck it is likely quite a good one.

I have a 4-jaw self-centring chuck and while it is good for perfectly round workpieces, it is not so good on anything that may not be. Being the diametrically opposite jaws that failed, I might suspect it was tightened, at too-full opening, on a piece of not quite round material.

I'm so used to three jaw scroll that I didn't notice that it was four jaw. Not much chance there as they are rare. The chuck can still be used as long as the capacity is reduced to a jaw opening which gives three undamaged teeth engaged in the scroll. I had thought of buying a four jaw scroll once, but they don't really have much practical use compared to an independent.

Looking at the jaws on the cheap Chinese chuck on my Warco, it's readily apparent that the damage seen in Niall's chuck would be very unlikely to occur, because all the scroll teeth are the full width of the jaw - none of them are on the triangle down to the grip face.

The Pratt Burnerd 3-jaw on the Myford Speed 10 I used to have showed the similar damage from when I bought it, and I've seen it on many other SC chucks.

I'm suspecting that (at least some) more recent designs are circumventing this vulnerability. It means sacrificing some capacity at the limit - and doing the changeover to external jaws at a lower diameter - or else positioning or extending the scroll further towards the chuck periphery. It looks a beneficial change to me.

Edited By Mick B1 on 06/06/2020 16:05:39

ARC have 100mm four jaw scroll chucks for £59 with both sets of jaws which would probably be a lot better than your tired old Pratt.

Hi Guys,

I've recently just bought a 100 mm 3 jaw scroll chuck from ARC. I'm quite impressed with it. In my opinion it is a better chuck than the PB one that came with my lathe ! Just a pity that its not a slim body one like the original chuck, the chuck sticks further forward by nearly two inches.

Just insert the offending jaw one rotation late. Mark it with a black permanent marker as an aide-memoirs . I have 3 sets of soft jaws just like that.

If you lose one tooth your capacity is effectively reduced by 1 pitch, if you have a minimum number of teeth that you need engaged in order to not break any more.

To check the capacity of the chuck, just remove the chuck and lay it on the bench. Remove the jaws and lay them on their sides next to their slots. Line up the teeth on the jaws with the scroll teeth and move them until at least two teeth overlap, not including the missing tooth. That will give a good idea what you can get away with for maximum diameter. Somebody tried to hold something with only one tooth engaged in the scroll and broke it off. It will always be the same jaw as that one is the first to end up with only one engaged. When you see the price of even second hand jaws, a new chuck from ARC gets more attractive.

The broken teeth on more than one jaw shows that the person had several episodes of stupidity.

Edited By old mart on 18/06/2020 19:50:40