Re: Rotary to linear translation - an interesting idea.

Thanks for all the input guys - I'm still not convinced one way or the
other, but the fact that building one, even carefully, is going to be
easier than thinking about it means that I'll just have to build one.

( Thinking is just so hard )

A few things to clarify here, from reading all the replies.

1. There is no need for gears to increase resolution. ( Which is a
good thing - even anti-backlash gears have SOME lash. Not much, to be
sure, but enough to be troubling in the context of a DRO ) Using the
Goldmine 4000 cpr encoders, a pulley of 2" circumference would still
read to half a thou. A 1" circumference pulley would read to 1/4
thou., but I'm troubled about using something that small.

2. There is VERY little contact between pulley and the strip - perhaps
5 degrees or so. Frankly, I've forgotten the exact value, but I
remember being very surprised by how small a number it was.

I had visions of an old Technics open-reel recorder, the RS1500, where
the tape wrapped around the capstan almost 200 degrees. ( This might be
one the only newsgroups where anyone even knows what an open-reel
recorder is <G> ) So I double-checked, and was informed of a very
small number.

3. Yes, this is a bit of a take-off on old floppy drive head
positioners.

4. In my testing and my enquiries, stainless shimstock is very high
quality material indeed.

5. In conversation with some of the surface physics guys around here,
even with shiny shimstock on shiny pulley, there will be lots of
friction to turn the pulley, with little worries about slippage. The
key is the high tension.

( They say this with great confidence, while at the same time admitting
they're only "pretty sure" they actually know what friction REALLY is. )

6. Of course it has to be shielded from swarf ! Thought that would go
without saying.

Alan








--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta