In a message dated 6/13/2004 5:20:21 PM Central Standard Time,
dg140@... writes:
Then gain, the bit is not for plexiglass or plastics, and ths speed might be
too high.<<
AH! Lexan or Acrylic. Then the "feed" must be right, and the "pull-up" must
be suitably fast, as "PC-board drilling-speeds" CAN melt that kinda plastic!
Particularly if the bit is not NEW-sharp!
The particular board which needs drilling is actually for the mechanical
part of the project. It has Thousands of holes, several hundred per square
inch.<<
I did a little thing like that with MY (Home-brew CNC PCB drill) and did
holes on 0.05" centers in acrylic. It was very clean; no melting. I think the
little piece of plastic was about 0.03" thick. I stuck it down with "Wallsaver"
poster tape (double-sided stickum by 3M). My machine would do about one hole
per 1.25 seconds, including fairly near traverse.
I've never been to a PC=drilling operation. How fast do they drill out the
boards? I'm looking at buying some kind of CNC machine sistem for light
work: something like the stuff from Taig Tools or Prazi.<<
The machine I saw had four "quills" turning at about 100,000 RPM (the
"motors" run on compressed air and literally SCREAM as they spin!), and the "peck
rate" is 4 to 5 holes PER SECOND! (for 0.1" IC-pin-rows; more for "scattered"
holes). These have "stacks" of one to seven "blanks" under each quill. If a bit
breaks, that quill will stop and ask the operator if the others should
continue, or shall the one with the busted bit "go get a new bit" and all continue.
All automatic. The danger here would be that the busted-off piece would be
still in the way, so a new bit would possibly get busted, too. It is wild to
see four quills all in a row stop, go back to the "start point", "dump"their
bits in the original holders, move over, "grab" new ones, and whiz back to work,
loosing maybe 5 seconds in all. Bang, bang, bang, at a rate of 4-5 "pecks"
per second. Machines like that cost over $100,000, yet pay for themselves
amazingly soon! Now, this was over ten years ago. That machine used 5¼"
black-cover floppies to transfer the programs from the "office" out to the machine.
Today, I don't know. Perhaps 3½" floppies the customers bring-in? And,
drill-schedules "from the office", if still done that way, surely via LAN! I have
not had reason to "visit" there in 20-25 years, so I have NO clue if they even
still operate. At ONE point during these years I have "been gone", their
front office called to inform that they "now did multilayer", so I could bring my
work to them! Hadda tell the lady I once did ONLY 2-sided PTH boards with NO
silk-screening, no solder-mask (which they LOVE to do, as there is MORE profit
in those "nice details" than the boards themselves!). So, maybe they are
still going strong.
Jan Rowland
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