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Default 6" 4 Jaw chuck Backplate

On Thu, 30 Oct 2008 14:45:20 -0700, Jim Stewart wrote:

Ricardo D. Medina wrote:
Hi,

I just bought a 6" 4 Jaw independent chuck for my Myford ML7, but I
can't get a backplate around here. What steel would you suggest I use
to make one? I was thinking along the lines of 4140, but if 1045 is
alright, it's easier to get here... Any ideas?


I currently fabricating a backplate
for a 5C collet chuck from a cast iron
round.


Just finished one for a 5" 4-jaw to fit on a asian 7x10;
6061T-something-or-other plate. It was thick enough and big enough and it
was in the pile of stuff-to-make-stuff-with.

Here's what I did, with a small trick I did to make mark the centres of the
holes for the chuck on the plate.

First off I mounted the plate straight to the spindle - three threaded
holes in the plate matching the spindle ones. That part was simple because
a while ago I made a good template for the spindle holes (after several not
quite so good templates). I screwed studs into the threaded holes and
bolted the plate on good and tight; then turned the front to match the
spindle nose. Turned the plate around and put the studs in from the other
side, bolted it down and indicated to make sure it was flat on the back
side, then turned the edge and the front to match the chuck.

Here's the little trick. I mounted the 4-jaw with the jaws gripping the
step on the front of the backplate. Adjusted the jaws until the outside of
the chuck and the back-side of the chuck ran true, then mounted a transfer
punch in the cross-slide and twiddled the hand wheels until the punch went
in one of the chuck mounting holes nicely. Took the chuck off, ran the
punch point up to the face of the backplate and scribed a circle. Measured
the circle dia, divided by 2^1/2, set the dividers to that and scribed the
centres.