# True Grip Chuck



## lensman57 (Dec 20, 2012)

Hi,

I have won a 4" Pratt Burnerd True grip Chuck on ebay, there are 3 adjustment screws that bear against the internal parts of the back plate. What is the correct procedure for truing the chuck for a particular diameter stoc? Do the back plate screws need to be loose or sung or tight while I am turning the adjustment screws? 

Many thatnks and regards,

A.G


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## chipenter (Dec 20, 2012)

A bit like adjusting a four jaw slacken the screw or screws opposite the hight spot , with a D T I and tighten all three .


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## modelman1838 (Dec 20, 2012)

Hi
I have a griptrue chuck on my myford and I use it all the time. The screws on the back plate should not need to be loosend or tightened each time, but should be tight enough to hold the chuck on but not over tight. The wedge action of the adjusting screws provide a good deal of force so the backplate screws can be fairly tight. On my chuck the backplate screws have not been touched for at least ten years.
What I particularly like about the griptrue is when the jaws become a bit
bell mouthed like they do on all chucks you can remove them and stone them flat as perfect concentricity is not a problem unlike normal chucks where the jaws must be trued insitu however you choose to do this.
Hugh


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## lensman57 (Dec 20, 2012)

Hi Jeff,

Many thanks for your reply. Do I have to loosen the integral back plate screws for adjusting the 3 adjustment ones or does it work with the back plate screws tight. I did open the bakplatd cleaned all the mock, that is how I know the inside of this chuck.

Regards,

A.G


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## deverett (Dec 26, 2012)

Now that you have cleaned the inside of the chuck, make sure you have just sufficient grease on the pinions, adjusters and in their sockets.  Too much and the inevitable swarf that finds its way in will not do the operating bits any good and centrifugal force will throw the surplus out anyway.

When you dial in the workpiece using the 3 adjusting screws, be aware that the chuck body moves in relation to the backplate.  Therefore, you need to have the backplate screws only tight enough so that the adjusters can move the chuck body relatively easily, but still hold everything firm.  Too tight and you will tend to strain the mechanism.

Dave
The Emerald Isle

Another long-time Grip-Tru chuck user.


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## lensman57 (Dec 26, 2012)

Hi Dave,

Merry Xmas, I will certainly do as advised. I need to gauge how tight is tight with regards to the mounting screws.

Many thanks and regards,

A.G


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## Marty Feldman (Dec 26, 2012)

If you have access to a copy of GH Thomas' Myford handbook, you will find a clear how-to discussion.


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## mu38&Bg# (Dec 26, 2012)

modelman1838 said:


> What I particularly like about the griptrue is when the jaws become a bit
> bell mouthed like they do on all chucks you can remove them and stone them flat as perfect concentricity is not a problem unlike normal chucks where the jaws must be trued insitu however you choose to do this.
> Hugh



I've not purchased an adjust tru type chuck because I use soft jaws. What I wonder about the statement above is that if you need very good accuracy, how do you ensure it without turning jaws in situ? If you take the jaws out and stone them how can you be sure the jaws are holding the stock concentric to the spindle axis? Do you check the runout in more than one place on the part to verify? What I'm saying is if the part is not concentric and you adjust the chuck position while checking only one axial location on the part, you may get a false sense of security. Of course this depends on how tight a tolerance you work with.


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## BobsModels (Dec 26, 2012)

AG

Go to this thread and there are instructions with a picture. I have several of these. the trick is to get the mounting screws just snug enough so the adjusting screws can move the chuck around takes a few tries but once set up you are good to go for a long time.

My additional recommendation is to set the chuck for a size that is the median of your work. I have found these a very accurate chuck and the run out very small when using different sizes. In my case it is set for .312 and I get about .0003 on .5 and virtualy 0 on .187.

http://www.practicalmachinist.com/vb/general/pratt-burnerd-chuck-help-141755/

Bob


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## lensman57 (Dec 27, 2012)

Hi and greetings to all,

Just wish to express my thanks to all of you for your help.

Regards,


A.G


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