So a good friend contacted me the other day saying he received a request for quote from a good customer, one he doesn't want to let down. He related that the customer wanted profiles cut into 6 inch diameter tubing. I thought about this for a while and had an idea.
Why not create a 'rolling fixture' for the tubing that will clamp in place using the clamps on the laser itself. This fixture is essentially a heavy gauge steel sheet with a few rollers that will 'capture' the tubing and 'fix' it in place, or just keep it from moving in the X axis. You will be the judge on how far apart the rollers should be to capture the tubing.
Then use a timing belt captured in some manner around the tube at a fixed location.
Also use a stiff piece of steel supporting a cut length of flat timing belt of the same pitch. My friend had a third clamp so this was easy for him. Now create a means where the flat piece of belting comes in contact with the piece surrounding the tube, perhaps some sort of spring to pressure the flat belt against the tubing 'belt'.
Create a flat layout of the laser cutting profile and use that to program the laser.
Of course you'll have to do some rather precise location of the origin of the profile to locate it atop the tubing centerline and at a equally precise location for the X axis. Precise being a relative term as it applies to your needs.
Running the program rotates the tubing as required during the cutting as the program runs.
I would assume he had to use a reduced linear cutting speed to prevent the tubing from popping out of being gravity held in location on the fixture. I would also assume the weight of the tubing would have an effect so this may not work for a light section.
Maybe it will work for you.
I did a quick mockup (ignore the scale) of the way I 'see' the layout, I'm not showing every detail but I think the 'smart' ones will grasp this concept. As always I welcome your comments.
He wouldn't share any pictures.