Homebrew PCBs

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!).


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