On Tue, Mar 16, 2010 at 09:37:11PM -0400, Gene Heskett wrote:
>
> Sticking a piece of pcb material, with the copper still on it, to a little
> used corner of the table shouldn't take more than something to clean the
> table down to bare metal so the superglue would bond well, and a tube of
> superglue. Solder the sense wire to a pulled up spare port pin, and a short
> jog to that location & a creep down till the port pin goes low, _should_ make
> an el-cheapo switch. The only fly I could see is that since the ground would
> assume to be through the spindle bearings, and they run on an oil film, it
> might not be too bad an idea to have a ground (wired also) spring against the
> tool shank or the bottom of the collet to assure the tool does have a good
> ground.
>
> I don't see any reason that sub thousandth accuracy could not be obtained if
> the copper film on the pcb is kept reasonably clean. Spindle stopped of
> course. ;-)
If tool lengths vary significantly, then on a short tool Z needs to creep
slowly down from the max length plus clearance, to shortest tool length,
to be able to stop before indenting an unsprung plate, AIUI. That's
lost time.
If the sense plate is spring-loaded, against the (known height)
underside of a pair of hold-down fingers, then it can be probed fast,
then slow after a retraction, like homing switches. I don't know what
that does to tooling, though. (I wasn't thinking of doing a flying rapid
during sensing.)
Erik
--
In all affairs it's a healthy thing now and then to hang a question
mark on the things you have long taken for granted.
-- Bertrand Russell
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