Jamie M wrote:
On 9/28/2012 9:39 AM, Stanley Schaefer wrote:
On Sep 27, 2:27 pm, Jamie wrote:
Hi,

I bought a 4" 3jaw lathe chuck off ebay, and am adapting it as a 4th
axis for my milling machine. The lathe chuck has a backplate with a
1.5" (1 1/2") spindle bore, and 1-1/2"-8 threads (8 threads per inch)

Is there an off the shelf pipe I could buy to thread into this and put
a couple bearings on the pipe to function as the lathe spindle? I
think
I might have to make this spindle on a lathe but it would be nice to
not have to!

cheers,
Jamie

It doesn't take long to do once you get set up. I made a dummy
spindle end for making chuck backplates, took an hour or so. That's
NOT a standard fastener or pipe thread. Or you could make a backplate
to fit whatever you're going to hook up the chuck to and fit it to the
chuck in place of the current backplate. Almost as much work as the
dummy spindle nose, I've done both. A three jaw wouldn't have been my
choice for such things, you can tweak a workpiece in a 4 jaw to be a
lot closer on center, but that's me.

Stan

Hi,

I think I will use some cold rolled steel tube, 1.5" OD and 1" ID, then
put the 8TPI threads onto that, hopefully the tube will work for 1.5"
ID bearings. What type of bearings would be good to use? I probably
will use two bearings I guess and would like to have some axial
pretension to get rid of axial play in the spindle, so need some axial
load as well as radial load bearings. Maybe a single thrust bearing
and a single roller bearing? Or an angular contact bearing and a
roller bearing maybe. Also what is the best mechanism to apply
the axial preloading?

cheers,
Jamie


Jamie,

For a 1.5" x 8tpi threaded spindle I would look at using maybe 2"
bar to start with so you can have an abutment for the chuck threaded
mounting plate to abut against. The various lathes I have used such as
Myford and IIRC Southbend are like this and the location is done by the
abutment and a short plain section next to it before the thread, not the
thread itself. If you look in your chuck you may well find a plain
before the start of the thread. In you chuck case can you remove the
mounting plate? it may need to if possible to true to get the best
running of the plate on your spindle.

Also consider how to lock the chuck from rotating on the spindle so that
cutting forces can't unscrew the chuck.

Also check prices on metric bearings as they are often cheaper due to
larger volumes, shouldn't be an issue if you're making the parts you
make it to the size required.