Re: Linear bearing types?

> For my applications, a vector-drawing machine was no good. I did
> build a light-beam writing pen for my large Calcomp pen plotter, but
> it really was a horror, and somewhat of a waste of time. I did use
> it while some conceptual and laser light source problems were being
> worked out, but the performance was pretty poor.
>
> My original plan, which is now fully operational and performing very
> well, was a raster drawing plotter. I wrap the film around a drum,
> which is conveniently machined to such a diameter that a multiple
> of the shaft encoder's pulses comes to a nice unit measured on the
> circumference of the drum. I used a drum such that the film's
> sensitive layer is at a diameter of 6.519". 6.519" x Pi = 20.480"
> If you had a shaft encoder with 20480 pulses per revolution, that
> would give 1000 pulses per inch. So, I got a 1024 pulse encoder,
> and attached a digital phase locked loop chip to multiply the encoder
> pulses by 20. It works very well, although several 'experts' told
> me it would be a cold day in hell before I ever got a PLL multiplier
> to work on a mechanical system.
>
> I have an optical carriage that slides on 2 1/2" hardened and ground
> shafts, on 3 Thompson linear bearings. The carriage is moved by
> a 5 TPI Kerk leadscrew with plastic anti-backlash nut. It works
> quite well, too. I had a cheap ballscrew without antibacklash on
> it before, and the positioning was erratic, due to the backlash.
> I use a 200 steps/rev stepper motor to move the carriage in
> .001" increments.
>
>
> Jon

Jon:

The reason I need the flatbed is to stationary mount the CO2 laser
outside the flatbed and run the optics/mirrors to the cutting head. By
doing this I can run it off HPGL files from inside AutoCAD's plot
function by using the pen colors for the strength(depth of cut) of the
laser and the pen up/down to turn on/off the laser. Your system does
sound like it solved you're problems, but now that I have explained
this, you can see why it would not be good for me cutting wood parts.
So, the search continues for an old flatbed plotter of 'D' size or
larger. If anyone knows of one about that they would like to part ways
with, please give them my email addie. I am also open to any other ideas
that our members may have if I can't find such a plotter. (maybe
construct a flat surface and use a printer driver on rails or
something...??)

Regards,

Don Hughes
Vancouver, BC Canada.

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