Re: Bridgeport Z axis drive
Posted by
Jon Elson
on 2000-11-27 11:55:52 UTC
Marcus & Eva wrote:
but the Bridgeport quill is QUITE beefy. Over 3" diameter, about 1/2" walls
most of the way up, and even with the quill fully extended, there's almost a foot
of quill still left in the casting! I have tried to measure a difference in stiffness
between quill fully retracted and fully extended, and I find that there is very little
difference! This is on an ancient round-ram Bridgeport base upgraded with
a Bridgeport J head.
stiffness reasons. I removed the entire pinion and shaft to prevent it
clunking as the quill was moved by the ballscrew. I would suspect
a backlash of .020" in the rack and pinion alone. If you adapt to the
fine feed handle, there is a worm drive that may add another .050"
to that, due to the worm driving the overload clutch, driving the pinion
shaft, driving the pinion. All those things have loose keys that add a
little more backlash, and it adds up to enormous backlash.
I mounted a ballscrew as close to the front of the spindle housing as possible,
and made a link from where the stop ring attaches to the quill to the
ballnut. I get about .001" backlash, mostly a flexing of this link.
Jon
> Hi Wally:Well, this may be true on lighter machines, benchtop mills and mill/drills,
> All of the commercial conversions I have seen, mount a small Z axis
> ballscrew to the quill.
> This is probably the least offensive way out of an intrinsically crappy
> situation.
> The basic physics you are up against, is that an extended quill flops around
> in X and Y, because it is cantilevered out so far.
> This makes heavy cutting impossible, and accuracy a hit or miss affair,
> depending on how far out the quill happens to be sticking.
but the Bridgeport quill is QUITE beefy. Over 3" diameter, about 1/2" walls
most of the way up, and even with the quill fully extended, there's almost a foot
of quill still left in the casting! I have tried to measure a difference in stiffness
between quill fully retracted and fully extended, and I find that there is very little
difference! This is on an ancient round-ram Bridgeport base upgraded with
a Bridgeport J head.
> Connecting the Z axis servo to the quill downfeed mechanism adds aThe rack and pinion mechanism is hopeless for accuracy, backlash and
> horrendous and variable amount of backlash to the equation.
> I can't guarantee it, but I'm pretty sure you will be disappointed if you go
> to all the trouble to make the mount, and then find you can't machine
> anything to closer than boilermaker's tolerances.
stiffness reasons. I removed the entire pinion and shaft to prevent it
clunking as the quill was moved by the ballscrew. I would suspect
a backlash of .020" in the rack and pinion alone. If you adapt to the
fine feed handle, there is a worm drive that may add another .050"
to that, due to the worm driving the overload clutch, driving the pinion
shaft, driving the pinion. All those things have loose keys that add a
little more backlash, and it adds up to enormous backlash.
I mounted a ballscrew as close to the front of the spindle housing as possible,
and made a link from where the stop ring attaches to the quill to the
ballnut. I get about .001" backlash, mostly a flexing of this link.
Jon