In a message dated 6/13/2004 7:52:33 PM Central Standard Time,
dg140@... writes:
How did you account for backlash in your homebrew CNC rig?<<
You DID see the photo in the PHOTO section under "Jan Rowland"?
I built that in '84, and was feeling CHEAP, so I did NOT spring for the
preloaded Turcite nuts sold by Ball Screws and Actuators, San Jose, CA. I bought
the "Single" Turcite nuts which have a 15/16"-16 threaded end for fastening
into the carriage or flange or whatever. I then carefully bored/tapped a hole
for 6-32 cap-screws through one side, and then I band-sawed through that one
side with the screw-hole so that inserting and tightening the screw would
"reduce" the I.D. This would tighten-up on the screw nicely, and obviously a "feel"
for HOW-tight was necessary. It worked, and has not been a problem needing
re-adjustment. These nuts are also more than twice as compact as the (spring-)
preloaded nuts, and MUCH less expensive. These screws are 7/16" dia.
1/8"-pitch, 4-start. Thus, one turn = 1/2" movement. So each step of the axis
steppers is 0.0025". Thus, I had to write my "Coordinate recording program" to
round-off each X and Y typed in to the nearest 0.0025" (not 0.001"). I realized
how cumbersome this would be (got USED to it!), but wanted the 1/2" lead for
SPEED of operation between holes.
What about those PCB drilling machines, what do they do for backlash and
other error components?<<
Of course, all lead-screws on such professional CNC $100,000 machines are
covered with bellows ("way-covers", etc.), so they are not viewable by a visitor
not willing to exhibit violence. I am however POSITIVE they are preloaded
ball-screws! AND, the screws are surely "precision ground", not the ROLLED type
also available.
"Other error components?" There are MORE? Uh . . . I'd guess MUCH care and
careful workmanship by folks who can READ (if you get what I mean!).
[Non-text portions of this message have been removed]