new life for old chuck

[old martParticipant @oldmart]

When we were given the Atlas 12 x 24 lathe, it had with it a very poor 5″ Pratt chuck and I discarded it after removing the backplate. Forgotten for years, I happened to find where it had been dumped and thought about the possibilities of getting it working again. The original hard jaws had been cut down and steel tops welded on and my first thought was to replace them with a set of better ones. We have loads of 5″ Pratt Burnerd jaws, but unfortunately although the teeth pitch matched the rest didn’t. I have photographed some of the proceedings, but didn’ think of taking pictures of the jaws before they were milled. There was enough left to make them simple tenon with 6mm screw holes. I used a 40mm shell mill with 4 APMT11 inserts and the welded and case hardened jaws used up both ends of a set of inserts taking the tops down to a starting height. The tenon slots were done with a 6mm solid carbide Totem endmill and they have ended up about 3.3mm deep and 10mm wide. The 5mm holes for tapping were drilled with a solid carbide stubb drill about 14mm deep. Tapping was definitely tougher than mild steel, but full threads are about 11mm deep now. The tops have yet to be made, I will use aluminium. I also shortened the inner ends of the jaws by about 6mm Which also meant loosing the end scroll teeth, but there are still 6 left and they do feed into the chuck correctly.

 

[old martParticipant @oldmart]

I have just got around to dismantling the Pratt chuck which varies somewhat from ICON’s recent thread on the screwed Myford version. This chuck has no thread and uses three 5/16W bolts to hold it to a backplate. The halves are secured by six 1/4W screws which needed help from an impact screwdriver to start moving. With three long 5/16W screws in the mounting holes, the halves can be jacked apart. I have never seen this design before.

 

[Howard LewisParticipant @howardlewis46836]

Obviously modified to take soft jaws.

Should be a useful tool when reassembled and fitted to a lathe.

Howard

[old martParticipant @oldmart]

The jaws that were in the chuck were not the originals, the serial numbers differ. I took a chance when I started work on the jaws before checking out the rest of the chuck, fortunately, the scroll is not damaged and is a good fit on its bearing, and the tee slots are in good shape. I have found a large block of aluminium, bigger than the spare made for the later 5″ PB chucks, pictured. The general idea would be large aluminium soft tops to hold delicate work. The rear half has plenty of room to add another set of three mounting holes, if needed.

[Nigel Graham 2Participant @nigelgraham2]

Good to see it restored to service, and usefully as a soft-jaw chuck.

I have an old chuck whose jaws have been bored out apparently to hold flanged workpieces, then a piece of steel welded (!) to the back to take a bench-mounting bracket. I think the previous owner was not necessarily the culprit but had used it as a sort of pipe-vice. So what you describe might point to a way to restore mine.

[old martParticipant @oldmart]

You might be able to grind off most of the unwanted top parts if you don’t overheat the lower part of the jaws. If you look at the side view of the jaw in the second photo, there are slight signs of the welding heat at the left hand end. Tapping would depend on the depth of case hardening and I chose 6mm, but might have got away with 8mm. This chuck will not be used for heavy duty jobs, we have lots of better candidates, so 6mm SCHS should be ok.

There are large numbers of chuck jaws on ebay, but many people mistake the numbers on them for part numbers, and not many can measure the tooth pitch properly.

[Andrew CrowParticipant @andrewcrow91475]

A while ago I gave an old chuck a new life as a 3c collet chuck, as I had a set of 3c collets for the George Thomas VHD I thought they might be a useful for the Myford, but of course they don’t fit the Myford spindle so I came up with this :-

Basically I removed the chuck jaw slots and attached a threaded adaptor to the scroll which draws in the collets as you turn the chuck key. On final assembly I bored the nose piece Number 3 morse to suit a Boxford adaptor I obtained from ebay.

Andy.

[old martParticipant @oldmart]

That’s a clever modification which may give inspiration for others to think about.

[old mart]

On 21 December 2024 at 20:18 old mart Said:

When we were given the Atlas 12 x 24 lathe, it had with it a very poor 5″ Pratt chuck and I discarded it after removing the backplate. Forgotten for years, I happened to find where it had been dumped and thought about the possibilities of getting it working again. The original hard jaws had been cut down and steel tops welded on and my first thought was to replace them with a set of better ones. We have loads of 5″ Pratt Burnerd jaws, but unfortunately although the teeth pitch matched the rest didn’t. I have photographed some of the proceedings, but didn’ think of taking pictures of the jaws before they were milled. There was enough left to make them simple tenon with 6mm screw holes. I used a 40mm shell mill with 4 APMT11 inserts and the welded and case hardened jaws used up both ends of a set of inserts taking the tops down to a starting height. The tenon slots were done with a 6mm solid carbide Totem endmill and they have ended up about 3.3mm deep and 10mm wide. The 5mm holes for tapping were drilled with a solid carbide stubb drill about 14mm deep. Tapping was definitely tougher than mild steel, but full threads are about 11mm deep now. The tops have yet to be made, I will use aluminium. I also shortened the inner ends of the jaws by about 6mm Which also meant loosing the end scroll teeth, but there are still 6 left and they do feed into the chuck correctly.

 

I also have a 5 inch pratt chuck that someone modified as per your method but using a set of soft jaws as the base. I made a further mod by drilling and reaming through the centre of the slot in both jaw and new jaw fronts then by using  hardened dowels it gives a repeatable location when I change the jaw fronts of which I have several sets.

Its a great way to increase the flexibility of the chuck without buying too many expensive soft jaws.

 

[DiogenesParticipant @diogenes]

Andrew, I like that collet chuck conversion, very good bit of lateral thinking..

[Andrew CrowParticipant @andrewcrow91475]

Thanks for the compliments both, but I had the idea from a 5c version that is supplied by ArcEuro although theirs looks very professional.

I didn’t do any plans other than on some scraps of paper just to get positioning of the parts in the right place. The only thing that was a bit of a light bulb moment was that the chuck body is reversed so that when you turn the key clockwise the collet closes as per normal chuck.

Also being a person that doesn’t like throwing anything away I’m always looking for a way to reuse whatever I can.

[old martParticipant @oldmart]

We have enough collet systems at the museum up to 30mm diameter. Apart from the dedicated Smart & Brown model A ones up to 3/4″, plus the stepped internal and external, we have er25 and er40 which can be used on both mills and both lathes, a huge choice.

I also don’t like throwing anything away that might be useful later.

[Andrew CrowParticipant @andrewcrow91475]

I had the 3c collets quite a long time ago before the er system became so widely available, I like them because they are very accurate and increase in 1/64 steps and they will grip short lengths when  necessary. Since converting the chuck I have also obtained some square and hexagon ones from Rotagrip in Birmingham, also made some of my own stepped ones.

Andy.

P.S What is the museum that you referred to in your previous message?

[old martParticipant @oldmart]

If you already have most of the expensive parts, it makes sense to complete the kit every time. The museum that I am a volunteer at is the Helicopter Museum at Weston Super Mare, I have been there over 17 years. I do have a little 7 x 12 lathe in my garage, but don’t use it much.

Visitors are not allowed into the restoration area, Health & Safety, as usual, and the machine shop is almost out of sight. I shall be going in tomorrow and might do a bit more to the chuck.

[JohnFParticipant @johnf59703]

Old Mart — see your messages !

[old martParticipant @oldmart]

I have completed the fitting of the tops, but have not yet decided whether to point the inner ends of the jaws. Since drilling the base jaws, I realised that if the screw holes were made equidistant from the tenon, the tops could be turned round if required.

 

[DiogenesParticipant @diogenes]

Looks good – may as well wait and let the work-queue dictate what happens to them next?

[old martParticipant @oldmart]

I have done away with the three 5/16W mounting threads, the holes have been opened up to 10mm which is much easier to get hold of, there was plenty of meat around the larger size.

[Harry WilkesParticipant @harrywilkes58467]

Old Mart do you (tongue in cheek) fancy taking these two on

H

[old martParticipant @oldmart]

Those pictures made me chuckle, the people with the lathes probably S—-T themselves. One of the chucks is a Sanou, by the look of it, we have at least three of them, hopefully not being abused, though. When I drilled and tapped the 10mm threads in the old Pratt, I was impressed by the high quality of the casting and our aluminium jaws will be used for holding delicate work, so the chuck will never be in danger of exploding.

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