Mini-Mill conversion
Posted by
Jon Elson
on 2003-05-31 23:32:53 UTC
I converted a mini-mill from Wholesale tool to CNC in a great big hurry
to demo my stepper interface board at the NAMES show in April.
I noticed something pretty odd about it, the X axis leadscrew has a
pair of opposed ball bearings under the handle, but the Y doesn't!
It just binds the handle up against the bracket/bearing to constrain
the leadscrew axially. I tore into it today and put a pair of cheap
bearings in it, and it seems to work a LOT better. I found 2 bearings
in my junk box that were 1.100" OD and matched the diameter of
the screw just behind the "flange" that is part of the screw. I left
the screw unchanged, and after boring out a bearing nest on each
side of the original bracket, that flange presses against the
inner race of the "inner" bearing, ie. the one facing toward
the table. The handle presses against the outer bearing's inner
race, and preload is adjusted through the nuts that hold the handle
on. I have modified a pair of McMaster-Carr sprockets by boring
them out to match the diameter of the original calibrated dials,
and bored and tapped 2 setscrew holes in the sprocket teeth. Hopefully
these holes won't cause damage to the belt. So, these sprockets fit
right over the handles where the dials used to go.
The bearings were .312" thick, and it worked out that boring the bearing
nests at 1.100" left enough of the original bracket to be sufficiently
strong. I also had to open up the sleeve hole all the way through by a few
thousandths to allow the screw to turn without rubbing.
One problem I had at NAMES was that I had to leave the nuts on the
Y handle pretty loose or the handle would bind up the primitive
bearing there. The nuts would eventually work loose, or tighter, and
throw things out of whack. Now I can have the nuts pretty tight
without the bearing binding up at all.
Jon
to demo my stepper interface board at the NAMES show in April.
I noticed something pretty odd about it, the X axis leadscrew has a
pair of opposed ball bearings under the handle, but the Y doesn't!
It just binds the handle up against the bracket/bearing to constrain
the leadscrew axially. I tore into it today and put a pair of cheap
bearings in it, and it seems to work a LOT better. I found 2 bearings
in my junk box that were 1.100" OD and matched the diameter of
the screw just behind the "flange" that is part of the screw. I left
the screw unchanged, and after boring out a bearing nest on each
side of the original bracket, that flange presses against the
inner race of the "inner" bearing, ie. the one facing toward
the table. The handle presses against the outer bearing's inner
race, and preload is adjusted through the nuts that hold the handle
on. I have modified a pair of McMaster-Carr sprockets by boring
them out to match the diameter of the original calibrated dials,
and bored and tapped 2 setscrew holes in the sprocket teeth. Hopefully
these holes won't cause damage to the belt. So, these sprockets fit
right over the handles where the dials used to go.
The bearings were .312" thick, and it worked out that boring the bearing
nests at 1.100" left enough of the original bracket to be sufficiently
strong. I also had to open up the sleeve hole all the way through by a few
thousandths to allow the screw to turn without rubbing.
One problem I had at NAMES was that I had to leave the nuts on the
Y handle pretty loose or the handle would bind up the primitive
bearing there. The nuts would eventually work loose, or tighter, and
throw things out of whack. Now I can have the nuts pretty tight
without the bearing binding up at all.
Jon