Re: Rotary to linear translation - an interesting idea.

Just wanted to relate some of my experience here. I experimented with
using a wheel on a goldmine motor encoder with my mill. I used a poly-
whatever skateboard wheel, and it actually worked pretty well with
good repeatability. Also by shimming and tighting the mounting bolts,
I could change the effective diameter of the wheel. The reason I gave
up on it and went to a steel wire setup is that, due to the size of
the encoder case, the skateboard wheel was about the smallest
diameter I could manage to get mounted without going to a gear train
type setup. This gave a circumference of around 10 inches, and the
minimum reading was just too much. With the wire setup the shaft is
5/16 and the reading is in the tens (just wish my work was). I still
like the idea of eliminating all the wire and extra hardware, just
haven't figured out how to do it yet.
Terry May

--- In CAD_CAM_EDM_DRO@egroups.com, beer@s... wrote:
>
> 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