Re: Stereolithograpy revisited

Grahm

Drilling holes requires hitting the intended spot as does cutting
out a shape or hitting the point of the uv-hardening-adhesive you
intend to hit. If you set up a machine and press the green button,
you sort of expect the thing to start cutting/drilling/marking or
whatever at the correct point, huh?

Most commercial systems from Lumonics, Baasel(now RofinSinar I
think), and Hitachi use granite instead of steel and those that
offer the option of a steel frame often require a pier isolated from
the building foundation. This is what it takes to get repeatable,
absolute indexed positioning of .0005" or better in 3 axes.
Not just microvias, but controlled depth skiving, resistor trimming,
micro-marking, or any of dozens of processes done daily in the high
tech industries.
Sure this differs from the processes run where lasers are machine
shop evolutions of mills, routers, oxygen torches and other classic
machine shop tools.
And also obviously if you wish to use sheer mass in place of
isolated/stabalized platforms, a big CNC laser for cutting steel
plate can just use adequately large beams/castings or whatever for
the frame.
In any case, I highly doubt many homebrew CNC Laser builders will
have a good experience with galvos, if they get them working at all.

Obviously there are systems made for shop floor use, but just like
normal "machines", temperature affects accuracy. Even new
commercial CNC machines with temperature compensation features are
only certified for a fairly narrow environmental range. I wonder
what a 10 degree change will do to the aimpoint of your unprotected
galvos? OOPS...there goes .001", maybe even .005" or more!!! Guess
we're back to conventional X-Y-Z axis motion for most of us.

Another issue with galvos vs. moving table or gantry is that when a
shape is cut out, the edges have a bevel related to the beam angle
of incidence galvo-to-table. If you have a cut line that
transitions from the right edge of one window to the left edge of
another, this will cause a visible reversal of the bevel direction.
And any tiny error in Z Axis focus will cause an X-Y misalignment at
the transition between windows on the table. Laser marking has less
problem with this as the beam/mode is typically slightly de-focused
anyway (mode shaping or intermediate optics), and there is no z Axis
dimension...just a surface effect.

Curious though, how much wattage at which wavelengths have you been
able to pump through galvos? I know this thread was mainly about
stereolithography, but it seems that most of the interest in hobby
CNC lasers is more along the lines of the mill/router design, and I
simply can't find available components to build a galvo system that
will survive being used in a laser system where the power level is
such that you can cut the materials people seem most interested in,
such as common metals or thicker organics. All I seem to find are
moving gantry or moving table.

Also, what software are people using for motion control with their
homebrew galvo systems? Sure, the X-Y-Z of the table is easy, but
what about the galvo control? And what are you using to post your G-
code? Not a trivial task to write the converters needed...





--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@...>
wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turyga1963" <TIntruder@>
> wrote:
> >
> > 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.
>
> no one mentioned drilling holes.
>
> > 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.
>
> Most commercial laser cutting systems (see synrad.com etc) using
> galvos have nothing like that.
>
> > Hmmmm...better budget for environmental control system that

keeps

> > the temperature +/- 2 degrees too.
>
> Laser marking systems are commonly used on the shop floor.
>
> I agree with your overall point but as commercial STL machines are

not

> operated in refrigerated rooms and do not have granite bases I am

not

> sure where you are getting this from. Perhaps micro via drilling

needs

> this, STL I doubt.
>
> Graham
>
>
>
>
>
>
> >
> >
> > --- 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
> > >
> >
>