What's new
What's new

z axis backlash on bridgeport


Jan 30, 2016
Does anyone have a retro fit for bridgeport z axis ...to convert to a screw vs. rack and pinion ? or a method to tighten what I have ? Ive installed ballscrews X,Y . Thanks
Which Z? The knee or the quill?
Gueesing you mean the quill since "rack and pinon". Fairly common gizzmos just put a screw and nut out front.
Thanks for that reply ......ive looked for pictures or videos and came up blank. Most commly done at the knee ?
Easiest to do the quill. Much less mass to move.
Here is one. https://www.homemadetools.net/forum/bridgeport-cnc-conversion-mechanical-87030
and another: https://www.centroidcnc.com/bridgeportkneemill.htm
Arguably the knee is better and has more range, better accuracy but you need some real serious power moving that load.
For more fun do both. Now it is a 4 axis and you can tilt the head and feed on a angle.

:dopeslap:Occurs to me to ask if this a cnc type retrofit or just power feeds on a full manual machine as I maybe answering wrong.
What are we trying to do?
Last edited:
My mill has a similar design as those. There is flex in the system (not backlash). The ball nut has no radial rigidity which the design needs. If you make your own add in a small linear rail/guide to keep yoke perpendicular to quill.
Most Bridgeport Z axis ballscrew conversions such as the Elrod (shown in the Centroid link), Southwestern Industries etc have the ballscew hanging way out the front of the machine, to clear the original feed stop mechanism. This isn't ideal. However, you can actually fit a 16mm ballscrew where the threaded feed stop bar was originally fitted. This reduces the overhang and gives you a more rigid result.
Here's how I did mine Z axis MkII Works nicely.
Here's another example, with the motor driving the ballscrew from above.
The skill is to minimise how much quill travel you lose, as this is a key drawback of CNC turret mills. My final version has almost the original 5" mechanical travel, although you will lose some of that due to the limit and home switches.