Homebrew PCBs

In a message dated 6/13/2004 5:20:21 PM Central Standard Time, 
dg140@freenet.carleton.ca 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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