Jan, that is a nice looking unit!
http://photos.groups.yahoo.com/group/homebrew_pcbs/vwp?.dir=/JanRowlandI couldn't find any other information in the Files / Homemade PCB Equipment
folder, am I just missing it or is there another place where I could get a
closer look on your design?
I'm especially interested in your description of "cheap" backlash system.
I'd love to see a close up of that.
As far as "error components" goes, has anyone looked at reducing the number
of joints required as a means of reducing error? And interesting idea is
that of using only two joints in a radial system rather than the 4 or more
required in a linear system.
http://www.massmind.org/techref/idea/lccam.htm scroll down
http://freeandeasy.sourceforge.net/ at the end of the paragraph about
"prototype XY table"
http://freeandeasy.sourceforge.net/rotary.phpRoller-skate bearings top and bottom on the main shaft were sloppy (as
expected) but when they are pressed towards each other, the compression
takes all the slop out and the result is very good. It reminded me of what
you were doing, but I don't think it is really the same.
---
James Newton, massmind.org Knowledge Archiver
james@... 1-619-652-0593 fax:1-208-279-8767
All the engineering secrets worth knowing:
http://techref.massmind.org What do YOU know?
Message: 21
Date: Mon, 14 Jun 2004 01:53:10 EDT
From:
JanRwl@...Subject: Re: bit cleaning while drilling 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!).