Hi Jan. How did you account for backlash in your homebrew CNC rig? What
about those PCB drilling machines, what do they do for backlash and other
error components?
---
>Particularly if the bit is not NEW-sharp!
> The particular board which needs drilling is actually for the mechanical=
>=20
>part of the project. It has Thousands of holes, several hundred per square=
>=20
>inch.<<
>I did a little thing like that with MY (Home-brew CNC PCB drill) and did=20
>holes on 0.05" centers in acrylic. It was very clean; no melting. I think=
> the=20
>little piece of plastic was about 0.03" thick. I stuck it down with "Walls=
>aver"=20
>poster tape (double-sided stickum by 3M). My machine would do about one ho=
>le=20
>per 1.25 seconds, including fairly near traverse.=20=20
> I've never been to a PC=3Ddrilling operation. How fast do they drill out=
> the=20
>boards? I'm looking at buying some kind of CNC machine sistem for light=20
>work: something like the stuff from Taig Tools or Prazi.<<
>The machine I saw had four "quills" turning at about 100,000 RPM (the=20
>"motors" run on compressed air and literally SCREAM as they spin!), and the=
> "peck=20
>rate" is 4 to 5 holes PER SECOND! (for 0.1" IC-pin-rows; more for "scattere=
>d"=20
>holes). These have "stacks" of one to seven "blanks" under each quill. If=
> a bit=20
>breaks, that quill will stop and ask the operator if the others should=20
>continue, or shall the one with the busted bit "go get a new bit" and all c=
>ontinue.=20=20
>All automatic. The danger here would be that the busted-off piece would be=
>=20
>still in the way, so a new bit would possibly get busted, too. It is wild =
>to=20
>see four quills all in a row stop, go back to the "start point", "dump"thei=
>r=20
>bits in the original holders, move over, "grab" new ones, and whiz back to =
>work,=20
>loosing maybe 5 seconds in all. Bang, bang, bang, at a rate of 4-5 "pecks"=
>=20
>per second. Machines like that cost over $100,000, yet pay for themselves=
>=20
>amazingly soon! Now, this was over ten years ago. That machine used 5=BC"=
>=20
>black-cover floppies to transfer the programs from the "office" out to the =
>machine.=20=20
>Today, I don't know. Perhaps 3=BD" floppies the customers bring-in? And,=
>=20
>drill-schedules "from the office", if still done that way, surely via LAN! =
> I have=20
>not had reason to "visit" there in 20-25 years, so I have NO clue if they e=
>ven=20
>still operate. At ONE point during these years I have "been gone", their=20
>front office called to inform that they "now did multilayer", so I could br=
>ing my=20
>work to them! Hadda tell the lady I once did ONLY 2-sided PTH boards with =
>NO=20
>silk-screening, no solder-mask (which they LOVE to do, as there is MORE pro=
>fit=20
>in those "nice details" than the boards themselves!). So, maybe they are=20
>still going strong.=20=20
>
>Jan Rowland
>
>
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