Re: Z axis conversion

Joe Vicars wrote:

> From: Joe Vicars <jvicars@...>
>
> Can someone point me in the right direction for info on converting
>
> the "Z" axis of a Bridgeport-Type mill. I'm reffering to the
> mechanicals of getting a backlash free mechanism. Is there a worm
> gear
> in there or what?

The hardware in the Bridgeport M and J heads is hopeless for CNC.
There is a worm drive from the fine feed handle to the quill pinion.
Then, the quill rack and pinion drive adds even more backlash.
I pulled the quill pinion completely out, and drive the quill by a heavy

coupling that attaches where the depth stop ring used to attach,
through the slot in the front. That coupling is driven by a ball screw
that sits about 1 inch in front of the mounting bosses for the old
depth stop rod. The whole mechanism clamps onto these bosses.
See a picture on my web page at :
http://ascc.artsci.wustl.edu/~jmelson/CNCconv.html
I think it is the 8th picture down.

If you need more detailed pictures, I think I have a few. I have
good drawings of the coupling from the ballnut to the quill.
But, there was a major measurement error when I attempted to
measure around those bosses on the front of the head, and make
sure the encoder would clear the belt housing. I ended up with
a mess, with shims, filed-down areas, washers and all sorts of
jury-rigging to get it in position to drive the quill and allow the
encoder to fit in place. So, drawings of my entire assembly
would be leading you the wrong way.

Jon