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Enlighten me on a Harding 4-Jaw chuck please

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petcnc

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#1
Looking for a decent 125mm 4-Jaw independent chuck I found a Pratt Burnrred one labeled "new but old stock and no longer manufactured".

The rest of the info on it is as follows:
Pratt Burnerd Light Duty 4 Jaw Independent Chuck
Body : High strength iron
Jaws : Case hardened and ground on fitting & gripping surfaces
Thrust Bearing : Case hardened
Operating screws : Acme form thread, machine rolled for strength. Hardened & tempered.
Body thickness 42.9mm
Bore = 25.4mm
Recess = 69.85mm
Mounting = 4 x M8 on 53.97mm P.C.D.
Suppied with one set of hard reversible jaws, chuck key and mounting screws.

125mm_Pratt_Burn.gif

As I need more info on that I made an inquiry and the man in charge of the company answered to me with those info:


It is a Pratt chuck that was made for Hardinge Lathes and has their name on it.
We do not have a data sheet for this as it is no longer made.
The light type refers to the fact that it is a thin bodied chuck used on small lathes.
It is brand new but at the moment the chuck key is missing and were are trying to find one.



QUESTIONS
Is (was) PB making chucks for Hardinge lathes?
As I do not have any experience on Hardinge lathes what system they use to support the chuck?
Do I need a special (ie made by PBA) mounting plate to fit this chuck to my 7X12 mini lathe?

Thank you
 
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middle.road

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#2
Should be able to make up your own mounting plate without any problem.
(4) mounting holes on the front face for M8's or 5/16" SAE Bolts.
Should be straight forward. A picture of the backside might help.
 

Chipper5783

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#3
I have a thin body 150mm (6") PB 4J, direct mount D1-4. It was original equipment on the Smart & Brown 1024. It is a very nice chuck. I really like the thin body, the over hang is reduced and you gain a little center distance.

It is not a heavy duty chuck, so don't crank down hard. 4J chucks hold really well, you don't have to crank down hard. Besides, you said this was a 125mm chuck - obviously it is not heavy duty!

What lathe are you putting it on?
 

mikey

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#4
Pretty big chuck for a 7X12" lathe. I know it will fit but it is on large side. PB chucks are high quality chucks and this one will need a back plate as Dan said, provided it is a plain back chuck. If it is threaded to fit a Hardinge spindle (I think they used a 2-3/16-10 threaded spindle) then it won't work. The cost they are charging for a brand new PB 4JC is quite fair for a chuck of this quality so if you need a chuck this big, I would jump soon.
 

petcnc

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#5
It is not a heavy duty chuck, so don't crank down hard. 4J chucks hold really well, you don't have to crank down hard. Besides, you said this was a 125mm chuck - obviously it is not heavy duty!

What lathe are you putting it on?
Believe it or not I plan to replace my cheapo 125mm 4-jaw on my 7X12 Lathe that was never accurate!

PC300376s.jpg

Pretty big chuck for a 7X12" lathe. I know it will fit but it is on large side. PB chucks are high quality chucks and this one will need a back plate as Dan said, provided it is a plain back chuck. The cost they are charging for a brand new PB 4JC is quite fair for a chuck of this quality so if you need a chuck this big, I would jump soon.
I use a 125mm (5in) chuck for years to my mini lathe and I enjoy the extra power I gained due the extra mass of the chuck (inertia) Of course I have changed the plain ball bearings of the Lathe for taper roller bearings.
 

markba633csi

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#6
What's wrong with your current 4J chuck? Jaws problems?
Mark S.
 

petcnc

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#7
What's wrong with your current 4J chuck? Jaws problems?
Mark S.
Yes Mark, jaws are not (never were) holding work vertically, plus I suspect, they suffer from the "bell shape effect" as they do not support work equally to front and back and to hold work I must tight them very firmly.
I must either replace the chuck for a decent one or I have to find a way to grind the jaws (making a toolpost grinder and find a way of doing that properly).
Petros
 

markba633csi

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#8
You could take the jaws out and grind them, unlike a 3 jaw scroll chuck which has to be ground in situ
Mark
 

petcnc

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#9
You could take the jaws out and grind them, unlike a 3 jaw scroll chuck which has to be ground in situ
Mark
I thought I must grind them while they were in chuck to achieve maximum accuracy... No?

I'm puzzled how I can do it accurately if they are removed from chuck....
 

markba633csi

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#10
Since each jaw adjusts individually you only need to grind each jaw face to be 90 degrees with some type of fixture or by eyeballing it
Yes?
Mark
ps if you had a milling machine you could clamp them all together in a row with the tips up and then with carbide tool mill the tips all at once or you could mill them one at a time for that matter-they don't need to be exactly the same length with respect to each other
 
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petcnc

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#11
Since each jaw adjusts individually you only need to grind each jaw face to be 90 degrees with some type of fixture or by eyeballing it
I do not trust my eyes anymore for that! I'd better use some fixture.
Thanks Mark
Petros
 

markba633csi

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#12
An accurate machinist's square would be helpful
 

Silverbullet

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#13
If the jaws are bell mouthed I'd be sure to grind them on the chuck . With them under holding pressure. , I suspect it's not the jaws but the chuck slots or jaw slots. .
 

petcnc

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#14
The guy gave me an extra £15 ($20) off for the missing key!
I think £186 is a fair price for a PB chuck, although postage is quite a lot (£37)
 
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