Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, Tom Benedict <benedict@h...> 
wrote:
> On Mon, 6 Oct 2003, Les Newell wrote:
> 
> > I have worked on and built a few CNC machines and I would 
recommend
> > supported rails rather than unsupported rods or pipe. You will be 
amazed
> > by how much an unsupported rod will flex. I used to use a CNC 
engraver
> > for routing shapes out of PCB with a 1.6mm cutter. It used 25mm
> > unsupported rails and I have seen it deflect by more than 0.5mm!
> 
> I'll second this.  If rod is all you can get your hands on, all's 
not
> lost.  You can cross-drill and tap drill rod, and make your own 
supports.
> 
> > If I was building a machine as cheap as possible I would use 
skateboard
> > bearings running on rectangular section cold rolled mild steel 
bar (AKA
> > bright mild steel). The bar can be bolted to your chassis (wood or
> > steel) for a really rigid setup. Bright mild steel is cheap and 
can be
> > reasonably accurate especially if you can go to your local steel
> > supplier and select the straightest piece they have got. If you 
don't
> > have a local steel supplier look for small engineering companies. 
They
> > are often quite willing to sell you small quantities of steel.
> 
> I'd also like to second the use of skateboard bearings.  In case you
> haven't priced bearings recently, they're uncomfortably expensive.  
This
> is even more true if you're looking at using an uncommon size.  
Skateboard
> bearings (and inline skate bearings, which have the same 
dimensions) are
> very very common, and people doing competitive skating have helped 
drop
> the cost on the things tremendously.  You can get a nice set of 
ABEC7
> ceramic skateboard bearings for about $25US, and they're massive 
overkill.
> A nice set of ABEC5 bearings will work quite well, and definitely 
won't
> break the bank.
> 
> Tom

There are other ways to support a machine than to have ridgid rails, 
but come clever engineering is needed.

btw, you didn't mention that a set of ABEC5 bearing is less than 
$20.00 US and a set is 16 bearings !

Dave