Boring a chuck

[kiramunch@sympa]

Has anyone ever bored out their 3 jaw scroll chuck. I have a 4" rotary table with a 4" 3 jaw chuck. The chuck has a 5/8" bore that I would like to open up to 1". Because the mill is a mini mill, I am limited to the sizes of rotary table and chuck that I can use. Any thoughts?

[HuFlungDung]

I would take the back off the chuck and look inside to see what diameter the scroll centering boss is.

Alternatively, you could remove one of the pinion gears and check its overall length. Using your deductive powers, you can estimate how far the small end of the pinion is from the center of the chuck. Then you'd need to decide if boring the chuck is going to expose the ends of the pinions, or indeed, cut the ends of the pinions off. The former will allow chip dust to possibly enter the scroll gear; the latter will probably take the edge off your boring bar if the pinions are hardened.

[packrat]

Do you mean the center hole? You would need to make sure its not going to leave the wall thickness too thin, between the scroll and the hole. Open the jaws up and look at how much material you have. To me, I would want at least .100 inch per side wall thickness.

cary

‎HuFlungDung , you beat me! I was typing while you posted.

[kiramunch@sympa]

Yes, it;s the centre hole I want to enlarge. I was also thinking or getting a spin indexer if I cant bore the chuck. I need to be able to chuck round plastic rod at 1.004 inches. Will a 1.0 inch c5 collet allow the 1.004 diameter rod to be chucked? Thanx guys

[BillTodd]

You are very unlikely to be able to bore the 5/8" hole to 1" (80mm chuck?) I looked a boring a 5" Cushman slightly and decided against it once I had it apart . Remove the jaws and look at where the scroll revolves around the centre hole, there is usually ~1/8"-3/16" minimum to support the scroll. Also remember the pinions usually protrude into the centre support (their holes will almost break through into the clearance hole)

Attached are pictures of a model of a 5" Cushman chuck with a 1-1/4" clearance hole - the real chuck has even less room for modification

Re: 5c collet : If memory serves, 5Cs are sold in 1/64" sizes so I would expect them to fit items +/-1/128" ( ~8 thou") in diameter, i.e. 1.004" in a 1" collet should be OK.

[kiramunch@sympa]

Thank you Bill and everyone else