Prat Burnerd Griptru adjustment

This topic has 7 replies, 6 voices, and was last updated 5 March 2025 at 21:26 by Paul Lousick.

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5 March 2025 at 15:19 #787345
vic newey
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@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?
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5 March 2025 at 15:41 #787352
Clive Brown 1
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@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.
5 March 2025 at 16:41 #787368
vic newey
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@vicnewey60017
On 5 March 2025 at 15:41 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
5 March 2025 at 17:48 #787378
Dell
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@dell
5 March 2025 at 18:18 #787381
Martin Kyte
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@martinkyte99762
Did you use the same chuck key pinion both times? You should always select a master pinion and stick to it.
5 March 2025 at 19:51 #787406
bernard towers
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@bernardtowers37738
Just done the Hemingway version of this on my std 3 jaw and it works really well.
5 March 2025 at 21:14 #787415
vic newey
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@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
5 March 2025 at 21:26 #787418
Paul Lousick
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@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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