Homebrew PCBs

Sure, but all you have to do is limit your working area to avoid the center
pivot. Step size is smaller near the pivot and larger away from it, but with
a nice linear microsteppng controller and some drive reduction (see the
pictures) neither extreme should be a problem. The calculations required to
convert x,y into polar are not terribly difficult, and the cost of the unit
goes WAY down because only a couple of components need to be precision.

Next objection? <GRIN>

Now back to those nuts... Did you measure the slop before and after
tightening? And did the friction increase?

---
James Newton, massmind.org Knowledge Archiver 
james@... 1-619-652-0593 fax:1-208-279-8767 
All the engineering secrets worth knowing:
http://techref.massmind.org What do YOU know?



Message: 10
   Date: Wed, 16 Jun 2004 11:02:26 -0000
   From: "ballendo" <ballendo@...>
Subject: Re: Turcite nuts, was: bit cleaning while drilling PCBsf

James,

Didn't see the link yet, but usually you trade one source of error 
for another. The probnlem with rotary-used-linear machines is that as 
the distance from the pivot changes so does the mech. 
advantage, "step" size, etc. And trying to make a linear move near 
one of the pivots requires a nearly instantaneous change in direction 
and requires acceleration far in excess of what most inexpensive 
drives can achieve...

There's more, but these are the bigge's

Ballendo 

In Homebrew_PCBs, "James Newtons Massmind" wrote:
>As far as "error components" goes, has anyone looked at reducing the 
>number of joints required as a means of reducing error? And 
interesting idea is that of using only two joints in a radial system 
rather than the 4 or more required in a linear system.
> http://www.massmind.org/techref/idea/lccam.htm scroll down
> http://freeandeasy.sourceforge.net/ at the end of the paragraph 
about
> "prototype XY table"
> http://freeandeasy.sourceforge.net/rotary.php
> 
> Roller-skate bearings top and bottom on the main shaft were sloppy 
(as
> expected) but when they are pressed towards each other, the 
compression
> takes all the slop out and the result is very good. It reminded me 
of what
> you were doing, but I don't think it is really the same.
>