Prat Burnerd Griptru adjustment

[vic neweyParticipant @vicnewey60017]

One of my lathes, a Holbrook, came to me in the 1980’s with a 5″ griptru chuck, I rarely use the lathe these days so decided to fit the chuck on another lathe I use all the time which has a 4″ chuck.  I made the backplate etc and noticed when fitted that a test bar in the jaws didn’t run quite true. I refitted it back on the Holbrook and see the same thing there.

So I set up a DTI and it looked way out. I began adjusting the 3 Allen keys while turning the headstock slowly and it began to improve. I got it almost spot on and then released the test bar and retightened it and it had lost some of its previous setting. I did this twice with the same result so what is the best technique to adjust these?

[Clive Brown 1Participant @clivebrown1]

The technique should be on-line somewhere.Turning an adjustment screw clock-wise moves the chuck body outwards  from the spindle centre-line. It’s important to release the other two screws say a turn or two before you do this to allow some”slack” to enable this movement. Also, the 3 screws at the back of the chuck should be firm but not overtight otherwise that movement will be difficult.

[Clive Brown 1]

On Clive Brown 1 Said:

The technique should be on-line somewhere.Turning an adjustment screw clock-wise moves the chuck body outwards  from the spindle centre-line. It’s important to release the other two screws say a turn or two before you do this to allow some”slack” to enable this movement. Also, the 3 screws at the back of the chuck should be firm but not overtight otherwise that movement will be difficult.

It says online to start by slacking off all 3 of the adjustment screws which l did, when you mention 3 screws on the back of the chuck then maybe that’s causing my problem, l’ll take the b plate off and see if l can loosen them and then retighhten

[DellParticipant @dell]

[Martin KyteParticipant @martinkyte99762]

Did you use the same chuck key pinion both times? You should always select a master pinion and stick to it.

[bernard towersParticipant @bernardtowers37738]

Just done the Hemingway version of this on my std 3 jaw and it works really well.

[vic neweyParticipant @vicnewey60017]

Thank you all for advice and Dell for the scan of the original instructions. I will take it all apart and start again tomorrow and see how I get on

[Paul LousickParticipant @paullousick59116]

The jaws and scroll may be worn or there may be dirt inside of the chuck and needs a complete strip down and clean.

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