Easing out the bore of a 3-jaw, s/c chuck

[GreensandsParticipant @greensands]

I have a very nice 3.25” O/D Prat 3-jaw self centering chuck which annoyingly will just not pass a 3/4” diameter rod stock through the bore. For example, a recently purchased length of aluminium rod measuring a dead 0.750” in diameter had to be reduced to 0.746” dia in order to enter the bore which seems a tad ridiculous. The answer I feel is to put the chuck up into the 5ins chuck and take say 0.005” off the bore but before taking such drastic action to a perfectly good chuck I am just wondering what others may think of the operation or have been faced with a similar problem.

[Michael GilliganParticipant @michaelgilligan61133]

I bet it’s bore is nineteen of those nasty furrin millimetre things !

MichaelG.

[David George 1Participant @davidgeorge1]

Hi I had the same problem with a Pratt chuck which was new and was 25mm bore I bored it to a few thou over 1″ bore with no problems now I can get 1″ black bar through to the spindle face which will only take 3/8″ diameter.
David

[Paul LousickParticipant @paullousick59116]

A Pratt chuck is fairly robust and you do not locate on the bore, so taking a few thou off the diameter should not be a problem.

Pratt Burnerd chucks were made in Halifax, so I doubt if is was made using those nasty furrin millimetre things !

[Michael GilliganParticipant @michaelgilligan61133]

For info.

https://www.colchester.co.uk/Data/Product_Downloads/Pratt_Burnerd_International_Workholding_Brochure_2022_Web.pdf

MichaelG.

[Clive Brown 1Participant @clivebrown1]

As said, no foreseeable problem with machining, but as the OP already has a 5″ chuck, then why bother?

[Clive Brown 1]

On Clive Brown 1 Said:

As said, no foreseeable problem with machining, but as the OP already has a 5″ chuck, then why bother?

I’m guessing the Pratt chuck might run truer.

[JasonBModerator @jasonb]

Why Bother? Could have better run out than the 5″‘, less wear and as members get older the smaller chucks are easier to lift.

Michael I thought by the description it was an old imperial chuck not a newer 80mm one.

[JasonB]

On JasonB Said:

[…]

Michael I thought by the description it was an old imperial chuck not a newer 80mm one.

Possibly  ‘transitional’
They obviously ended-up going for 19mm

MichaelG.

[old martParticipant @oldmart]

Going to 0.754″ would be fine, but you should strip out the chuck so that the minimum of parts have to be cleaned after the boring. Cast iron dust gets everywhere. Going larger would take careful evaluating of the design of the chuck. Make sure the OD of the body is running true before boring.

[JasonBModerator @jasonb]

How do you get on machining cast iron parts if you don’t want the swarf on the chuck?

As for dust I aim for chips and a minimum amount of dust.

[Author]

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