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

Advert

New Replies

Report Bug

Help/FAQs

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

This topic has 12 replies, 9 voices, and was last updated 7 April 2025 at 19:31 by old mart.

Viewing 13 posts - 1 through 13 (of 13 total)

Author

Posts
6 April 2025 at 21:32 #792242
Greensands
Participant
@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.
Advert

6 April 2025 at 22:28 #792252
Michael Gilligan
Participant
@michaelgilligan61133
I bet it’s bore is nineteen of those nasty furrin millimetre things !

MichaelG.
7 April 2025 at 07:02 #792261
David George 1
Participant
@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
7 April 2025 at 08:45 #792265
Paul Lousick
Participant
@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 !
7 April 2025 at 08:52 #792267
Michael Gilligan
Participant
@michaelgilligan61133
For info.

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

MichaelG.
7 April 2025 at 08:55 #792268
Clive Brown 1
Participant
@clivebrown1
As said, no foreseeable problem with machining, but as the OP already has a 5″ chuck, then why bother?
7 April 2025 at 09:02 #792269
Bo’sun
Participant
@bosun58570
On 7 April 2025 at 08:55 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.
7 April 2025 at 09:04 #792271
JasonB
Moderator
@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.
7 April 2025 at 09:44 #792272
Michael Gilligan
Participant
@michaelgilligan61133
On 7 April 2025 at 09:04 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.
7 April 2025 at 15:21 #792303
old mart
Participant
@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.
7 April 2025 at 15:35 #792306
JasonB
Moderator
@jasonb
How do you get on machining cast iron parts if you don’t want the swarf on the chuck? Anyway I think the bodies are SG iron which machines more like steel than grey iron

As for dust I aim for chips and a minimum amount of dust.
7 April 2025 at 17:34 #792329
John Purdy
Participant
@johnpurdy78347
I had the same problem with my 4″ PB Griptru chuck. It would not take a piece of 1″ stock in past the jaws, the bore was just shy of 1″. I removed the jaws, centred the body, and skimmed a few thou out of the body with no problems. worked well as stated by others. After doing it I dismantled the chuck and gave it a good clean and re-lube.

John
7 April 2025 at 19:31 #792340
old mart
Participant
@oldmart
If the body parts are SG iron all the better, but there is also the depth inside that has to be bored. I’m never afraid of dismantling and cleaning a chuck. That said, I did fully dismantle a 6″ Toolmex 4 jaw independent for machining the body, and it was probably more trouble than it was worth,especially getting things lined up so precisely so that the grub screws went in easily.

Somebody has a P B 80mm three jaw for sale on ebay and the label just says “iron body”.
Author

Posts