drive leadscrew? or replace?
Posted by
ccs@m...
on 2001-12-14 10:58:20 UTC
Now that I've made the ballscrew crosslide conversion work
satisfactorily, I'm recontemplating a full 2 axis conversion of my
larger (13" south bend) lathe, which raises the question of how to
move the Z (carriage) axis. (It's amazing how seeing part of the
project move can make ones outlook more positive)
One option is to drive the threading leadscrew. I do this on my
smaller lathe, and it works okay - plus I can disengage the half nuts
and manually move or reposition the carriage. But there is
substantial backlash, and driving the screw would require milling
about 3/4" off the tailstock end bracket (about 1/4 to 1/3 of its
length) so that enough screw would project for an 11/16" bore
"trantorque" bushing to attach a pulley.
The other possiblity would be to hang a new screw - probably a
ballscrew, but possibly an acme screw with moglice nut - behind the
bed. The nut(s) would mount on a bracket that would bolt to the back
of the carriage via some existing bolt holes, and could be
disconnected and allowed to hang out of the way below the screw when
manual operation or leadscrew threading was desired. My major
concerns with this are what it will be like to drive the carriage from
behind the bed, especially when the major load on the axis is on the
front in the rack and pinion manual handwheel and associate gears, and
also the fear that the whole system will self destruct if the
leadscrew or power feed is ever engaged while the rear cnc drive
bracket is attached.
I'd give driving the existing screw an experimental try, if it didn't
mean milling a lot of material off the support bracket, or figuring
out how to accurately reproduce it.
Any thoughts?
Chris Stratton
-------------------------------------------------
Christopher C. Stratton
Engineer, Instrument Maker, and Horn Player
ccs@... 617 628 1062
http://web.mit.edu/~stratton/www/brassbuild.html
satisfactorily, I'm recontemplating a full 2 axis conversion of my
larger (13" south bend) lathe, which raises the question of how to
move the Z (carriage) axis. (It's amazing how seeing part of the
project move can make ones outlook more positive)
One option is to drive the threading leadscrew. I do this on my
smaller lathe, and it works okay - plus I can disengage the half nuts
and manually move or reposition the carriage. But there is
substantial backlash, and driving the screw would require milling
about 3/4" off the tailstock end bracket (about 1/4 to 1/3 of its
length) so that enough screw would project for an 11/16" bore
"trantorque" bushing to attach a pulley.
The other possiblity would be to hang a new screw - probably a
ballscrew, but possibly an acme screw with moglice nut - behind the
bed. The nut(s) would mount on a bracket that would bolt to the back
of the carriage via some existing bolt holes, and could be
disconnected and allowed to hang out of the way below the screw when
manual operation or leadscrew threading was desired. My major
concerns with this are what it will be like to drive the carriage from
behind the bed, especially when the major load on the axis is on the
front in the rack and pinion manual handwheel and associate gears, and
also the fear that the whole system will self destruct if the
leadscrew or power feed is ever engaged while the rear cnc drive
bracket is attached.
I'd give driving the existing screw an experimental try, if it didn't
mean milling a lot of material off the support bracket, or figuring
out how to accurately reproduce it.
Any thoughts?
Chris Stratton
-------------------------------------------------
Christopher C. Stratton
Engineer, Instrument Maker, and Horn Player
ccs@... 617 628 1062
http://web.mit.edu/~stratton/www/brassbuild.html