I leaned something new about my old chuck today

[Defender92]

I just wanted to share this because I was surprised a self centering 3-jaw chuck could be this accurate.

Long story short I figured this Pratt Burnerd chuck was junk. It came with my Clausing Colchester 13”. It was hard to move the jaws in spots. I opened it up today, cleaned and greased it. In that process I leaned it had 4 adjacent screws that pressed on the backplate that worked like a 4 jaw chuck.

I got it dialed in to about .001”. I verified this with another gage pin. That’s about the same as my Hardinge-Sjogren Speed Collet Chuck!!

Anyways. I’m very happy about this and figured I’d share if there was any other amateurs out there that didn’t know about the adjustment screws.

I also stamped a mark on the backplate to ensure it’s mounted on the same pins every time.

View attachment trim.CBF7B398-9A91-41CB-A99B-3D5DF4442A8C.MOV

 

[mmcmdl]

Long story short I figured this Pratt Burnerd chuck was junk.

Why would you even think this ????? It's one of the best chucks made .

 

[Dabbler]

I have Pratt Bernerd chucks because I think they are the best I can afford.

 

[brino]

....so set-true or set-tru or set-rite or something....depending on who patented what name.
Brian

 

[Ironman2]

It's called a Poor Man's Set True. I have done that to several chucks, including the one I have on now.
Due to imperfections in the scroll and gears, if it is set true using a 1" pin, it will be true within a range, say 1/2 to 1.5" and then go off.
I have 3 different sized bits of shafting for zeroing so I have coverage up to 6"

 

[darkzero]

....so set-true or set-tru or set-rite or something....depending on who patented what name.
Brian

Pretty much. I heard Buck was the one who invented it but I don't know the truth in that. Buck = Adjust-Tru, Pratt-Burnerd = Setrite, Bison = Set-Tru, Gator = Tech-Tru. Those are just the ones off the top of my head, I'm sure there are others. And Tap-Tru is what I call my beater chuck that I undersized the backplate register & adjust runout by tapping.

 

[Firstram]

Tap-Tru FTW, I have a cheap 5C collet chuck set up like that! Do I need to send you royalties?

 

[brino]

And Tap-Tru is what I call my beater chuck that I undersized the backplate register & adjust runout by tapping.

Will, is that name patent-pending?
Brian

 

[darkzero]

Will, is that name patent-pending?
Brian

I came up with the name all on my own but I'm not the only one who has called it that. I've seen other people call it that but long after I thought of it. Of course I learned about the idea from others so surely someone has had to have called it that before me. But I won't refuse any royalty payments. Haha!

 

[mmcmdl]

Just saw this one Will . Yes , we ran flat back chucks on the large grinders and simply brought them in true with lead hammers and tightened the bolts . Always able to bring the shafts in within .00005 which was called out . I always wondered why nobody does this on a lathe as it is so simple .