Pratt/Burnerd 4 jaw Dismantling ?

[Martin KyteParticipant @martinkyte99762]

Hi Everyone

Does anyone have any idea how to dismantle a Pratt/Burnerd 4 jaw independent chuck. Is it even possible. I have a good one with a broken adjuster screw and a very old one with good screws and I would like to swap one of the screws over. Any ideas please.

regards Martin

[Martin KyteParticipant @martinkyte99762]

Pratt/Burnerd 4 jaw Dismantling ?

[Clive Brown 1Participant @clivebrown1]

Hi Martin, from memory, the screw is retained by a "dowel" which has a fork that engages the waist in the screw. You will have to devise a tool for pressing the dowel out towards the rear face of the chuck. AFAIK, it's just a press fit, but there might be a retaining grub-screw visible .

[Brian WoodParticipant @brianwood45127]

Hello Martin,

The jaw adjustment screws are held in place between two jaws of a hard plug inserted from the back of the chuck. In one design these are held in location with a side screw, fitted from the back of the chuck, locking the plug in position. Unscrew and tap the plug out with a slim pin punch acting on the visible face beside the waist in the jaw adjusting screw

A second design dispenses with that arrangement and in this design the plugs have been pressed in and these are rather more difficult to remove. They have to be driven out with a slim blade shaped tool acting on the face of the jaw, it has to be slim to work in the space left available by the waist of the adjusting screw. The width should be equal to the face width of one jaw to give it the maximum cross section to work without buckling

Support the chuck on something solid but with space behind each of the plugs to give it somewhere to go as it moves. Heat at each position helps in expanding the bore and gently tap each plug out, remembering that they are hard and therefore prone to chipping. Once the plug has moved sufficiently it is possible to grip it in a slide joint pair of plumbing wrenches and wriggle it out.

Regards Brian

 

Edited By Brian Wood on 04/09/2020 14:11:24

[old martParticipant @oldmart]

PB used two types of thread on similar sized chucks, square and ACME. You can compare the teeth in the jaws to easily check. I was in the process of repairing a very worn 6" PB and after making four screws, I was dismayed to find that the plugs which you are in the process of removing were all cracked. This prompted me to give up and I got very lucky buying a NOS Toolmex for just over £106. The square holes are smaller than PB ones, and consequencly, the ends are less likely to crack.

I always use a strap wrench to unscrew the chuck, and never use a "cheater" for more key leverage.

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