steel tube build concept - 1500y,1000x,250z

[outtastep]

all good questions , ill attempt to bluff my way through
......

Ok, there's a few things you need to look at. How are you going to get to all the bolts to fasten on the bearings to the gantry and Z axis?

gantry - steel tube 3mm, drill and tap thread , or weld threaded rod to tube ?
x carriage - aluminium plate and angle bolted togeather, rails bolted through
z axis - maybe thicker plate 20mm ?

Are you welding everything, if so how are you planning to take the inevitable distortion out if the frame, gantry and Z axis? Epoxy? Shims?

i worried about this, maybe only weld below y rails and shim them out to put y rails on then above this bolt together

The Z axis with the back plate does nothing for stiffness, think of a cornflake packet with the top and bottom cut off, and only makes it harder to align everything as adds more complication.

so better just to have stiffer plate ? and forget sides

What thickness steel are you using? There's no problem in using steel but it will need bracing to stop it bending and twisting.

3mm , lots of jigs and clamping

On an all steel machine (if thats what yours is?) you'd be best connecting the steppers to the ballscrews with belts and pulleys, this will stop any resonance from feeding back to the stepper motor.

very good suggestion, my current machine has no issues like this as it is so sloppy no resonance builds up !
Can't comment in the plasma thing as no experience with them, I'm sure a dual machine could be built but as with anything that doesn't do just one thing, there will be compromises.
thanks for persevering with my somewhat undeveloped project ,
cheers
ben