This is what you want:
http://www.milinst.com/robotics/5_300s.jpg. This is
sold as a kit to schools. Laminated MDF, drawer slides and doesn't even use
screws, it uses dial cord, like found in old radios. I can hear the "you
must use gold plated ball screws" crowd having a fit from here.
Brief details here:
http://www.milinst.com/robotics/robotics.htm#axis,assembly manual here:
http://www.milinst.com/robotics/5_300mnl.pdf They claim 0.1mm accuracy, with 20 holes per min, and I see no reason to
doubt them. You're not going to mill steel on this, or churn out 1000
boards a day, but that's not the point. You could be faster by hand, but as
you say, it gets old after the first few.
If you tried to carve wood with this machine then the amount of flex comes
into play, but for drilling it just isn't relevant.
You could replace the cable drive system with screws. Say you used threaded
rod with a 1mm pitch, a single rotation will move the table 1mm. A lot of
steppers will do 200 steps per rotation, so your table will move 1/200mm per
step. In the real world it won't, of course, but getting decent accuracy
isn't that hard. You find a lot of 48 step motors too, but they tend to be
low power. Still enough to push that table about though.
The software can compensate for backlash, but isn't ideal as the amount of
backlash varies, given the screws will wear more in different spots. On the
flip side, it won't kill your wallet to buy some new threaded rod.
One way to preload the table is to use tape measures. You may not have
noticed, but they exert a constant force no matter how much tape is pulled
out. They use coiled springs, like in clocks (aka negator springs).
Tony
> -----Original Message-----
> From: Homebrew_PCBs@yahoogroups.com
> [mailto:Homebrew_PCBs@yahoogroups.com] On Behalf Of Richard
> Sent: Sunday, 10 December 2006 6:48 AM
> To: Homebrew_PCBs@yahoogroups.com
> Subject: Re: [Homebrew_PCBs] Wooden CNC router
>
> Thanks Tony, After I stay up all night on a coffee buzz,
> building circuits and boards and stuff, I know My old eye
> sight is't all that great and I can still drill a few hundred
> holes by hand with handheld dremel and 032 carbide bit and
> you know that my hands proabably aren't all that steady at
> that point :) I bet I have busted 1/2 a dozen carbide drills
> over the years hand drilling so that's not to bad. It's just
> that doing it by hand isn't as fun as it was when I did my first one !
>
> My worst expriences is trying to cut to size my PCB's without
> causing bodily injury! Dang them dudes don't cut all that
> great. My best method is a die grinder and vut off wheel
> then polish to size while cleaning up the edges. I like the
> upside down, table mounted jig saw I had seen, but I'm not
> sure how well that would work out.
>
> I've been wanting to do this for some time, and just never
> sit down and do it. I heard of some folks pre-loading their
> X-Y tables with rubber bads in ordered to help minimize the
> "slack". It's almost like using an old worn out lath, where
> you always turn out to far then slowly go back in intil your
> where you need to be on the dial. Kind of a backlash removal process.
>
> The electronics portion for me should be pretty easy, just
> the hardware for the XYZ slides has me a little baffled on
> what to use and where to get.
>
> Thanks for the replies..
> Richard