PDA

View Full Version : How would you do this? (chuck fitting)



Timleech
12-30-2006, 05:28 AM
I need to adapt a couple of chucks to my DSG lathe, which has a simple spigot and 4-stud flange on the spindle. The only thing I have to fit the spindle so far is the 3-jaw which is probably the original, 52 years old.
First off is a 16" 4-jaw which originally had an integral L2 fitting. I bought it unused or almost so 6 years ago, it's had very little use since. I adapted it to fit my TOS, with C6 spindle, by hacking off the threaded projection and machining the C6 taper direct into the body. This I did by clamping the chuck backwards onto a 3-jaw in the lathe and indicating it true from the body before machining. That wasn't a huge success, parts held in the jaws would 'wobble' slightly relative to the axis. My guess is that I didn't have it quite as true as I had thought, but it makes me think twice about doing the same again. The alternative is to bore and face it on the mill, but that'll require some *very* careful setting up, tramming etc to get a decent result. Either way assumes the face of the body is square to the jaws, but it is a decent quality (Pratt, I think) chuck.
Any recommendations, anyone been there before?
After I've done the 4-jaw I have a faceplate and 12" 3-jaw to do, but at least by then I'll have the added option of setting them up in the 4-jaw.

Thanks
Tim

Ian B
12-30-2006, 06:06 AM
Tim,

For holding the chuck back to front for machining the rear register, would you not be better off taking the jaws out and clamping it to a faceplate? Then you only have the radial displacement to worry about, as the face should run true. Some jacking bolts fixed to the faceplate might be handy for moving it into position radially.

Ian

Ian B
12-30-2006, 06:10 AM
oops - just re-read your post; you don't have another lathe with a big enough swing to mount the 4 jaw?

If you go the mill route, how about mounting the chuck on a rotary table; tramming then becomes much less of an issue as the chuck body will be true to the axis of rotation of the table.

Ian

Timleech
12-30-2006, 06:15 AM
Tim,

For holding the chuck back to front for machining the rear register, would you not be better off taking the jaws out and clamping it to a faceplate? Then you only have the radial displacement to worry about, as the face should run true. Some jacking bolts fixed to the faceplate might be handy for moving it into position radially.

Ian

Ian

Bit of chicken & egg here, the faceplate I have also has the C6 fitting & needs adapting. I was going to do that in the 4-jaw ;)
Also it's (I think, haven't yet measured) slightly smaller OD than the 4-jaw, which would make clamping the 4-jaw to it a bit fiddly (there's not a huge clearance between 4-jaw & lathe bed).
I can probably get the faceplate set up in, or clamped to, the 3-jaw or do that in the mill if I decide that's the answer. The faceplate can of course be trued up after fitting, not so with the 4-jaw.

Thanks
Tim

ulav8r
01-01-2007, 03:02 AM
A better way to hold the chuck might be to chuck up a large piece of stock in the 3 jaw, turn it to get it running true, then clamp the jaws of the chuck you are fitting onto the stock. This will hold the chuck true if the jaws are in good condition.

Timleech
01-01-2007, 02:49 PM
A better way to hold the chuck might be to chuck up a large piece of stock in the 3 jaw, turn it to get it running true, then clamp the jaws of the chuck you are fitting onto the stock. This will hold the chuck true if the jaws are in good condition.


What I've done in the end is to clamp the chuck jaws directly onto the lathe spindle, which has a 1" long 5.25" dia. spigot. The chuck was pressed very firmly against the spindle whilst clocking it to run true on the periphery. The end result is passable if not brilliant, I'm getting of the order of 4 thou runout measured 9" from the chuck jaws on a bar which has been clocked true at the jaws.

http://web.onetel.com/~duttondock/Pictures/4jaw-1.jpg

http://web.onetel.com/~duttondock/Pictures/4jaw-2.jpg

Thanks
Tim