Les,
I would use 7/16" drill rod for 12" machines with 6" beds that
mill and drill PCBoards. Use the roller blade bearings for larger
machines that make signs and toys. My 7th Sojourn uses roller blade
bearings and window channel. It can do large trace boards but the
smaller Brute has better accuracy.
John
--- In Homebrew_PCBs@yahoogroups.com, "Les Newell" <les@l...> 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!
>
> 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.
>
> Allthread quite accurate enough for drilling and PCB milling. If
you use two
> preloaded nuts then backlash should not be a problem. For the
larger sizes
> of allthread you can buy extra long nuts that are used as couplers.
They
> seem to have less backlash then ordinary nuts.
>
> Les
>
>
>
> > --- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan
> > <stefan_trethan@g...> wrote:
> > > John,
> > >
> > > thanks, but this is way of what i asked.
> > >
> > > i know there are other options, i know there is drill rod.
> > >
> > > but i hoped you may tell me which surface your gas pipes have.
> >
> >
> > The problem with galvanized or cast pipes is that the surface is
very
> > rough. a few minutes with a file followed by some sandpaper can
> > offer a smooth surface.
> >
> > fixed upper bearings and spring loaded lower units can allow for
the
> > differences in pipe diameter.
> >
> > My point of view is that if you can get your hands on something,
do
> > it. then look for better stuff as you go !
> >
> > Dave
> >