Hi, all - I've decided that putting any more effort into trying to keep my Chinese prusa clone alive is just a waste of time. I'm going to start fresh with my own design.

The build area is going to be a 4mm plate of aluminum measuring 18" X 18". The design will be an ultimaker approach, in which the head moves along the X/Y axes in the top of the printer, and the platform descends slowly along the Z axis.

The 18" sq. bed will be heated by 4 - 200 watt plastic heater mats, and run from 2 - 450 watt 12 volt computer power supplies. I'll be using one thermistor in the center of the build plate, feeding that to a (probably generic Melzi) controller, and switching the load through a solid state relay. Not sure how I'm going to fasten the mats to the bottom of the bed, but Liquid Nails home product repair adhesive LN-201 seems like a possibility. Good up to 300 F, and will stick to both metal and plastic. I guess the other alternative would be to create a sandwich with another metal plate. More weight and cost.

I'm curious as to whether 8 mm rods will be sufficient to support the print head, or whether I should use 10 or 12 mil rods. I'd like to keep the weight/mass of the moving head as low as possible, but I don't want the damn thing to sag in the middle. Any thoughts?

I haven't decided on a Z axis dimension, but it will probably be in the vicinity of 24 to 36 inches. I think the primary consideration here is convenience in getting filament started; a 36 inch build height suggests about a 3.5 to 4 foot machine height, which is inconvenient to work on the top of when it's sitting on a counter. Outside of this consideration, I cannot think of any other Z axis limitation. Anyone got any thoughts on this?

I'd like to support the build plate in all 4 corners, but this is probably going to result in 4 stepper motors, which is a tad pricey. The other alternative would - I suppose - be one large-ish stepper motor driving a continuous belt around 4 shafts. (Assuming you can even buy a continuous belt. Don't know, but haven't seen one.) Anyone with thoughts on this, please chime in. How have others done it?

Actually, that turns out to be a real problem. I need a continuous circular belt, not a straight length of timing belt cut on both ends. Anyone know where to source that? I've come up dry.

I haven't decided on a frame structure. I was thinking copper pipe; In 1981 I made an entertainment center out of standard half inch copper pipe, 90 degree and tee fittings all held together with metal epoxy, and the damn thing is still as solid as a rock, 35 years later. My concern is mounting all the internal components. (But copper pipe, burnished to a satin glow and sealed with a clear epoxy, could look really cool.)

Any thoughts, please fire away. Thanks!

Charlie1