Re: Stereolithograpy revisited

The fact you can purchase a surplus galvo is nowhere near making it
work with lasers.
In order to drill a hole in the right place, it has to sync
perfectly with the correct laser pulse and be absolutely steady when
it does.
Using them for laser light shows? fine...close is good enough.

Using them to drill holes where your tolerances are .001"? Well, I
can tell you from experience that even the correct manufacturer's
part won't always work well enough. Seen it happen and had to spend
a lot of money to replace them.

If you plan on using galvos effectively, you also better plan on
buying a really big and heavy granite optical bench to mount
everything on and provide rigidity for the entire system, galvo,
motion, and beam path. Keep your cell phones away too....galvos
that actually work with lasers, and are commercially available at
the present are also affected to the point of mis-positioning by
certain transmitting cell phones. Remember, if the mode spot on the
workpiece only moves .001", the positional change of the galvo
(although angular, not linear) is probably less than .000001" given
the typical galvo-to-table distances common today in equipped laser
systems.
Hmmmm...better budget for environmental control system that keeps
the temperature +/- 2 degrees too.

We haven't even touched on the software yet. Need to control a lot
of movement too: X & Y on the table, Z in the optics, and U & V in
the galvos? How about aperture control?

Ditto pulsed lasers and their usual requirements for power, optics
and control.

Quite frankly, galvo-based systems (unless you restore a "salvaged"
galvo equipped system you bought surplus) are not practical for the
average hobbyist.

The gantry style that is more like a router or mill that uses a CW
laser is more practical and the whole thing is technically
achievable by most CNC hobbyists. (I consider the hobbyist as one
who actually uses the machine to engage in their hobby...not that
the machine IS the hobby)

The big thing remaining to do is to find a laser that will cut what
you want to cut.

Tom

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:
>
> Graham Stabler wrote:
>
> >--- In CAD_CAM_EDM_DRO@yahoogroups.com, juan gelt <juangelt@>
wrote:
> >
> >
> >>has everybody had a chance to expound on his opinions?
> >>very well, now here are some facts:
>
>>http://www.technology.niagarac.on.ca/people/mcsele/lasers/index.htm
l
> >>
> >>
> >>
> >>
> >
> >Firstly your assumption is that just because you can make a UV
laser
> >it must be suitable for stereo lithography but I doubt you have
any
> >idea if that is the case or not. I don't.
> >
> >
> >
> Yeah, the Nitrogen transmission line laser is usually run at 1 -
10 Hz
> rep rate.
> It would be pretty hard to do any real assembly with only 10
pulses per
> second.
>
> >What I should of said was we can't afford galvos anyway, my real
point
> >being there is not much point worrying about issues pertaining to
> >technologies that are out of our reach (practically). I was
refering
> >to the post directly before mine only.
> >
> >
> >
> Actually, galvanometer-mirror drivers can be found on the surplus
market
> (they
> used to use them in direct-writing oscillographs 50 years ago) and
they
> wouldn't
> be that hard to make, either. I have some little ones, basically
two
> wires suspended
> in a magnetic field, with a tiny mirror glued in the middle of the
wires.
>
> Jon
>