Re: [CAD_CAM_EDM_DRO] Z Axis Mechanical Layout Options - Bridgeport M Head

Hi Mark ,
I bought a clone mill (FIRST with 50 x 10 table) a couple of years ago. It
had been retrofitted with SERVO Products controller and 3 axis drives.
When I bought it it wasn't fully working. Had a couple of electronic
problems which the folk at SERVO gave me wonderful help with and I was able
to fix.
However the Z axis had been adapted locally with a mixture of tooth belts
and gears ( they had done a frightening amount of work to produce a crappy
result) to drive the quill pinion and it was not working and the previous
owner seemed to have had continuing problems with it.
From bits and pieces I had learned from this group and elsewhere I decided
this approach was not for me, so I started from scratch and built a quill
drive using a screw positioned where the depth stop screw was fitted .
There was a retrofitted mill at my place of work so I was able to have a
good look at it , though I did not copy it exactly. I had room to fit a
double tooth belt drive to the screw which enabled me to mount the motor
vertically at the side and with a second short belt turn the drive at right
angles and drive the screw. This enabled me to keep the block mounted on
the front of the quill short and consequently reduce the cantilever effect.
I used a piece of acme screw material (good quality stuff) and a matching
bronze nut. I cut the nut in half and built an adjustable anti backlash nut
assy. At the time this cost $96 NZ which was about 1/6 of the cost of a ball
screw and I wanted to be sure things worked.
Of course , guess what I found in a second hand machinery dealers shop 6
weeks later .... a brand new 16mm ballscrew with nut the right length , for
$160NZ !!! So I now have that stowed away for insurance .
However that was nearly 2 years ago and the Z-axis has been working fine .
About 1.5 thou of backlash last time I checked, but I can live with that for
the work I have been doing.
I did manage to stuff up one particular time and drove a cutter straight
down into a block of plastic when the motor was still switched to manual and
didnt run.
Broke the belt and gave me a heck (I'm trying to be polite) of a fright .
However a new belt fixed it and didnt do any other damage.
I can email you some photos if you like . Perhaps I should tune myself in to
how to put pics on the group files . It is much easier to follow on a
picture.
I definitely would not consider driving the quill rack and pinion though.
Backlash can be a major pain and the rack has not been designed for
measurement accuracy, that comment comes from guys way back on the list and
others ,not just me.
If I can help lets know
Regards
Graeme

----- Original Message -----
From: "natchamp_87" <mark@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, November 19, 2002 12:31 PM
Subject: [CAD_CAM_EDM_DRO] Z Axis Mechanical Layout Options - Bridgeport M
Head


> Well, I got my new (to me!) BP M head mill. I have already started
> taking it apart for the clean up, ball screws, etc. One of the
> things I have not resolved is the best way to accomodate the Z axis
> travel. I am hoping someone can shed some light on the best way to
> accomplish this.
>
> If I move the quil, it appears there are a couple ways to do this.
> 1) mount a motor to turn the same shaft as the hand lever. This to
> me has a problem of very long travel for a given rotational travel of
> the motor, unless I severly under drive the pulley which still might
> not be enough?
> 2) mount a motor to turn the fine feed shaft and worm gear. This
> would fix the long travel per motor rotaion in 1 but the worm gear
> isn't fixed to the shaft, it works on friction. I could key-way the
> worm gear onto the shaft? This, to me, seems like the best approach
> for moving the quil.
>
> If I move the knee I would need a bigger motor and could still under
> drive to address the higher torque required. However, there doesn't
> appear to be any good mounting locations for this method.
>
> Can anybody shed some light on this? I know people have done this
> many times and would love to hear some insight. Thanks a bunch.
>
> Mark
> mark@...
> www.mark.hargett.com
>
>
>
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