Re: Lasers::Comments & Questions fo the List

John Stevenson wrote:

>
> From: john@... (John Stevenson)
>
> On Wed, 12 May 1999 11:28:48 -0700, you wrote:
>
> >From: Don Hughes <pencad@...>
> >
> >John:
> >
> >Thanks for the reply, yes, you will be of great help as I go down this
> >road. What I need to first know is either the best or safest way of
> >mounting the laser to the base of the machine table. Should it be
> >mounted stationary, beside/away from all the axis' and use mirrors to
> >convey the beam, or mounted on the gantry and use the beam directly
> >through the focal optics with no mirrors at all?
> >
> >Also John, what is the most commonly used software for controlling
> >lasers in cutting operations. I am mostly wondering about the turning
> >on/off and the percentages of power control. I will be cutting mostly
> >lite ply up to 1/4" thick and balsa up to 3/8" thick for model aircraft.
> >The software would ideally control both the laser and the motion, so I
> >would need some insight along this road as well. I read in a previous
> >thread here that IndexerLPT has a great range of uses, do you feel this
> >may be useful as it uses a HPGL file directly to do the cutting profile?
> >
>
> >Thanks very much,
> >
> Firstly let me make it clear that I am a mechanical engineer and have no part
> with the electronics of the lasers but I can ask and get info on that subject.
> A bit of background first on the company. They have 6 lasers A to F from 1Kw to 6Kw. the first one [ C ] is in mothballs due to lack of room. This is a moving X and Y table machine with the fixed laser mounted above the table firing down through the head by one 45 degree mirror.

By having the lasers mounted this way, are they moving with the gantry?
If so, does this effect the gases inside the tubes at all? I don't know
if I mentioned it to you at all, but I plan on using a Synrad 40 watt
CO2 laser. These do not need to have extra cooling devises and I have
seen a 25 watt Synrad in operation and it did not quite cut through the
thickness of the wood that I will be using. Let me clarify that it did
lase through alright, but there was much distortion and a second cut was
needed, so it was decided that a 40 watt should do the trick.

> Machines A,B,D, and E are virtually identical with a moving X axis, the bed and
> the head moves on linear rails to provide the Y axis. Again the laser is mounted
> above to save space and protect it from fork trucks. The beam is taken through
> three mirrors at 45 degrees to take the beam along, down and then along again to
> the last mirror which travels on the top of the head on the Y axis.
> The last machine F, was new at Christmas and is the big 6Kw model.
> This one has a moving gantry that moves in the x axis and on the gantry is the
> moving Y axis. The laser is floor mounted behind and fires through two 45
> mirrors to the end of the gantry then to the top of the head. On all machines
> the beam is contained within alloy tube 4" in diameter other than inside the
> travelling Y axis and these are inside a metal enclosure. There is no way that
> any stray beams can be seen.
> All machines are on ball screws except the latest one which is moved by
> precision rack and pinion, Max certified error is 0.002mm over 1000mm.

I will be using ball screws with Thompson rails or similar. Although
the weight of the gantry is minimal, it's the linear motion acceleration
weight that concerns me because of the cutting speeds that can be
attained.

> probably why this machine cost nearly 1/2 million pounds UK.
> All machines are on AC servo's with encoder feedback.
> As regards software anything that can move motors under say G code instruction
> will work. Note though that the main enemy of laser cutters is having software
> that pauses between moves, this will burn the work. I use Ahha controllers on
> milling machines and although I am a big fan of Ahha I feel that it's not up to
> commercial laser applications, note I said commercial.

For now this will be between my friends, but if I find that things
perform nicely, I will turn this into a commercial application.

> Programming can be done by any software that can handle canned cycles or macros
> as you need to start to cut off the work and then move into the cut, similar to
> the approach depart moves like in Bobcad V17.
> You mention controlling the power, I must admit this is a bit of a grey area of
> my knowledge but I will ask tomorrow when I am there how power is controlled.
> Possibly it is done by altering to input voltage / amperage to the laser.
> Some controllers can alter spindle speeds by using analog output to inverters,
> perhaps this is a way?
> Some laser cam switch off and on rapidly, others have to startup so they stop
> the beam by swinging a thermal block into the beams path. if this is done close
> to the laser output the beam is not concentrated and the excess heat is carried
> away by having the block water cooled.
> HPGL would be one way to go. A laser doesn't need a true Z move, it just needs
> to be about 1/2 to 1mm above the work. 'My' machines do this by using a LVTD to
> track the work and control a servo motor on a Z ballscrew.

Universal Lasers, of the U.S., markets small application machines that
have table sizing of 12"x24" and 18"x24 ". This was the system that I
had demoed for me at the salesman's shop, and he inputted object lines
by using CorelDraw and another text editor for engraving applications,
and I did not get the name of that. Now he was able to manipulate the
power to the laser in percentages and had a stop/start somehow. This is
the part that I am missing on. Was that machine using an HPGL device
controllers from typical programs and let's say an AutoCAD plot
controller for power ranges by the color of pens, and the on/off by the
pen up/pen down command. If this is the case, then I can use my AutoCAD
and import to the computer screen and cut from that I would think. Do
you agree?

> It could also be done manually by lowering it on to the work with a slipper
> giving the correct hight, be careful though not to drop down into any holes.
> The pen up / pen down signal from the HPGL file could be used to fire the laser.
>
> >What steppers have you found to give the ideal results in controlling
> >gantry's, 130 oz./in. or higher motors? The effective cutting table size
> >I desire is 36"(Y) x 48"(X). I am still toying with the fact that do I
> >want this to be just a laser cutter, and a mill if I can do this, or
> >just have two separate machines? I will need to machine plugs for
> >cowlings and gear pants, canopies, etc. from 3D files for vacuum forming
> >of these parts.
> >
> Sorry I can't answer this the first part of this but remember laser cutting is
> much different from milling as it is a non contact process and there are no tool
> or side forces to contend with. and the last part precludes the use of HPGL
> files as you will need a Z axis for milling.
> If you haven't already I would suggest you look at Ahha's web site at
> http://www.ahha.com download the demo and read the manedit.txt file in the demo.
> Even if you don't want to use their controller the information is good
> groundwork.
>
> Sorry if this has been a bit long but like most things the learning curve is
> rather steep to start

I understand, and many thanks for being patient with me as I start my
learning curve. Things are coming clearer in certain areas now with
everyone's input, and especially yours John.

Thanks again,
Don Hughes
Vancouver, BC Canada

>
> Regards,
> John Stevenson
> Nottingham, England
>
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