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Newbie with a chuck query

Three jaw chuck serial numbers not matching

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Colin Wilks25/03/2019 12:18:16
30 forum posts
2 photos

Hello all,

Just setting up a workshop in order to repair/ restore my two Austin Sevens.

I have bought a Myford Super 7 from 1974, which has a three jaw chuck which seems miles out as far as run out is concerned. I am at the stage of trying to level the lathe up and wanting to machine a length of material to check for taper. Before I go any further I want to clean the chuck, which is full of swarf and grime.

It is a 100mm Burnerd 30M marked "Specially made for Myford ML7 Lathe". The face is marked 1,2,3 next to the jaw slides. The back plate has a serial number, 86371. The pinions are marked 1, 3, 3 (ie I've got two 3s and no 2). The jaws are marked 1,2,3 and numbered 103522, 111218 and 111218.

Am I right in thinking the numbers mismatch is not good news and I've got a "bitsa"?

I am fortunate that the lathe came with

Any info/advice most welcome.


Maurice25/03/2019 13:53:29
459 forum posts
50 photos

Hi Colin; welcome. The differing numbers do not sound good, but I'm not sure. However, until recently you could buy replacement sets of jaws from Burnerd. The chucks were made accurately enough to make this practical; and cheaper than a new chuck. I am assuming they are still in business! Having got a chuck with matching jaws, I think you need to pay some attention to the backplate. Before I go further, is it actually a separate backplate, or do you just mean the back of the chuck? The reason I ask is because the chucks "Specialy made for Myford" usually had a threaded body, not needing a separate backplate. If it does have a separate backplate, then it may not have been machined on your lathe, and will need remachining, or if it's not thick enough to allow this, then you may have to get a new one.


David Standing 125/03/2019 15:03:51
1288 forum posts
48 photos

Colin, you do have a set of mismatched jaws.

Pratt Burnerd are very much still in business, part of the 600 Group that owns, amongst other things, Colchester and Harrison.

If looking for a new set of PB supplied jaws, make sure you are sitting down first.

The 3 jaw 30M chucks might be made for Myford, but they do have a separate backplate, it is just they were supplied with the correct backplate for Myford.

It is more likely a jaw problem than a backplate problem.

It will probably be cheaper to get a good s/h chuck than buy a new set of genuine PB jaws from PB.

For starters, I would try and borrow a known accurate chuck from someone nearby and try that on your lathe, so you know the chuck is the problem.



Edited By David Standing 1 on 25/03/2019 15:05:16

not done it yet25/03/2019 15:48:16
4487 forum posts
16 photos

You might improve concentricity by moving the jaws to different slots. shouldn't make much difference, but it may do - they don't number the jaws and original positions for nothing. The dirt and grime will noit improve matters, either.

Plasma25/03/2019 17:14:52
388 forum posts
45 photos

Yep looks like someone was careless with the chuck jaws, you will need a new chuck or set of jaws.

Colin Wilks25/03/2019 17:49:27
30 forum posts
2 photos

Thanks all. My message was chopped off before posting and should have included fact that the back plate is separate, held on by three 1/4 BSF cap head bolts. There are three other holes on the back plate tapped 1/4 BSF and I assume these are to jack the plate off?

Luckily I got some collets with the lathe, so can proceed without the chuck but wanted to know my options.

Sounds like a new/second hand chuck is called for. I bought this through a dealer and it was mentioned that the previous owner had mislaid the three jaw chuck but had bought a replacement. I suspect what I've got is an ebay special!

It is a lot of years since I used a lathe and then it was pretty amateurish, so I have no doubt I'll be back with more questions.


Brian Wood25/03/2019 17:53:53
2141 forum posts
37 photos


Before you spend a lot of money, what sort of error are you getting? Jaw 1 could have a broken off piece right at the smallest section that engages with the scroll, it is the weakest part and the normal fitting sequence of jaws 1-2-3 will give a very large error. [about 1/3 of the scroll pitch which will be about 40 thou eccentric.

Look and see if that is the case; if so all is not lost! Install the jaws in the order 2-3-1, ie with Jaw 1 last and if they are a reasonable set you should see a marked improvement. Whether that is then acceptable or not only you can judge

Did you get both the inside and outside jaws with the lathe?



Edited By Brian Wood on 25/03/2019 17:55:27

Maurice25/03/2019 19:23:34
459 forum posts
50 photos

Following Davids's reply, I have just examined my three jaw and four jaw chucks, stamped "made for the Myford ML7". The were purchased new in about 1970. Neither of them has a separate backplate. This does not help with Collin"s problem, but I think that replies on the forum should not be dismissed simply because they seem unusual. And I do know what a backplate is!


Emgee25/03/2019 19:48:53
1445 forum posts
212 photos

I also purchased a 100mm 3j SC chuck from the Myford stand at the MEE early 1990's it was made especially to fit direct to the spindle, the threaded part was attached to the back of the chuck by front mounting screws so I guess you could say it was on a backplate, however it may have been part of the scroll.
The jaw numbers were matching to the chuck number stamped into the back of the chuck, or backplate if you must, I sold it on this forum about 2 years ago, still in fine working condition.

I would be wary of buying a chuck that did not have matching jaw/chuck numbers.


Edited By Emgee on 25/03/2019 19:50:27

Mike Poole25/03/2019 20:20:13
2538 forum posts
60 photos

I doubt you will ever find the missing jaw so to sort out what you have will probably mean grinding the jaws so they match the chuck. The fact you could buy a new set of jaws must mean the scroll and teeth are held to a pretty tight tolerance and I believe new jaws are made to be a tight fit in the body so some fitting should be required so I would keep the jaws you have. If the jaws are an acceptable fit in the body then after a good clean and close inspection for any burrs or damage I would grind the jaws. There is plenty of info around on the net about jaw grinding.


Hopper25/03/2019 23:29:36
4389 forum posts
92 photos

There was even an article in a recent MEW magazine (Issue 267) on grinding the jaws of a PB Myford chuck, including dimensions for making the simple "clover leaf" plate to hold the jaws in the outward position while grinding. All else you need is a common Dremel type grinder and make a bracket to hold it in the toolpost.

Howard Lewis26/03/2019 08:27:16
3132 forum posts
2 photos

If you follow Hopper's advice, which would seem to be an easy way out, since you have two jaws marked 3, you need to identify which one should go in slot 2. The jaws will be hard, so it may be difficult to engrave them, (You are unlikely to be able to stamp them )

Somewhere, I have a new set of jaws for a PB chuck, must check the size!. If they would fit, you are welcome to them.


Howard Lewis26/03/2019 08:27:16
3132 forum posts
2 photos

If you follow Hopper's advice, which would seem to be an easy way out, since you have two jaws marked 3, you need to identify which one should go in slot 2. The jaws will be hard, so it may be difficult to engrave them, (You are unlikely to be able to stamp them )

Somewhere, I have a new set of jaws for a PB chuck, must check the size!. If they would fit, you are welcome to them.


Hopper26/03/2019 08:38:27
4389 forum posts
92 photos

Depends too on how much out of true the jaws are sitting. Regrinding is good for up to maybe .010" or so of runout but much more than that, apart from taking forever to grind off, will leave a very wide gripping face so you will lose the ability to grip very small diameters, like say 1/16" or so. But still, it's better than no useable chuck at all I suppose.

If your runout is too great, you might even be better off to scout around for a used #2 jaw to install before regrinding. Or even a complete set if you can find them. The do come up on eBay from time to time. (EDIT: See Howard's generous offer above. Gotta love the ME forum!)

Meanwhile, bodging being the better part of valour (discretion is way over-rated), if you can measure the runout, you could just use a piece of packing strip between that jaw and your piece of bar to get going doing your initial set-up turning tests.

Edited By Hopper on 26/03/2019 08:42:25

Edited By Hopper on 26/03/2019 08:44:27

Simon Williams 326/03/2019 10:09:54
492 forum posts
78 photos

Original post says he has three pinions, 3,3,1 ; can't see that's going to matter too much. It's not ideal, but it's a second order correction.

He also has three jaws which I would call a mismatched set in that he has got 1,2,3 but different serial numbers. How much error this will introduce is anyone's guess, but if they fit in the correct slots (and subject to the above comments about missing teeth or a damaged scroll) this should give a usable if not precision chuck. There's a lot of good work come out of a poorly chuck by dint of machining everything at one setting.

If the concentricity is close but not close enough then we might be into jaw grinding territory. I'd be chary of committing to this except as a last resort.

Some of the posts above seem to have got fixated on not having a 1, 2 3, set of JAWS, this isn't the case.

What would be interesting to know is how far out of true the chuck is with all three jaws fitted. If it's country mile out then there is something wrong with the teeth or the scroll. This might be helped by shuffling the jaws or putting them in with one tooth delayed, but it's a long shot and is going to be a PITA for all time, Interesting but not serviceable.

Given a lathe is only as good as the chuck, bite the bullet and buy a new (i.e. replacement) one. Nothing wrong with buying another second hand one with all the jaws but be choosy. Alternative is three (six including the outside jaws) new jaws - money well wasted since we don't know the scroll isn't damaged and we've still got the riddle of the mismatched pinions which indicates this chuck has some sort of bodge-it history going on.

HTH Simon

Ian S C26/03/2019 10:51:53
7468 forum posts
230 photos

I have use of a Box-Ford A with a Burnerd 4" three jaw chuck, I had quite a battle getting things right until I found that one jaw had had the first tooth broken off, A bit of fiddling around and its ok(sort of).

Ian S C

Chris Trice26/03/2019 11:02:59
1362 forum posts
9 photos

Did it come with both sets of jaws? If no then it will be cheaper to source a new (second hand) chuck. It's such a basic but necessary and central part of lathe turning, it's worth starting off with a "good" chuck rather than trying to compensate for a bodged one.

Hopper26/03/2019 12:23:38
4389 forum posts
92 photos

Sorry, for some reason I thought it was 1,3,3 jaws. If the jaws are 1,2,3, then regrinding should be pretty simple to bring them back to concentric.

Misnumbered pinion should not make any critical difference. It's just a gear to turn the crown wheel.

Chris Trice26/03/2019 16:06:19
1362 forum posts
9 photos

Colin is a relative beginner. Talking of regrinding requires at the very least a grinding spindle or Dremel with a suitable tool post mounting and making/buying the gadget for holding the jaws open at their tip and you'll still be left with a chuck that won't hold anything smaller than 1/8th", assuming his efforts are even successful. Seriously, just buy another chuck because you will eventually anyway when the shortcomings of the first rapidly get annoying. Since the one supplied has obviously been swept up off the floor from under a bench somewhere, the scroll and inner workings could be well knackered. Even PB say it's often more expensive to repair than replace. I'm reminded of a friend of mine who used to work as a car mechanic and the customers that used to think a £25 service would make their 200,000 mile car like new.

Colin Wilks26/03/2019 18:05:06
30 forum posts
2 photos

I'm not too worried about the odd pinion but the jaws are a mismatch, 1 x 103522 plus 2 x 111218. I've got a Dremel and can set it up to grind the jaws, but for now I'm going to strip the chuck down and clean it out and go through the large box of various bits that came with the lathe. The third 111218 may just be lurking somewhere! I have a feeling Chris Trice is correct and a new chuck will be the outcome, but this one needs cleaning out anyway, so I have nothing to lose by stripping it and seeing where I get to.

Many thanks for all the interest and advice. I'll come back and let you know what happens.


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