Offcourse you can copy it - this is "open source engineering", so you should!
I have also looked at tubes (had som 12mm lying around, easier to saw than stainless steel, smaller sizes might be too bendy) but this would also mean deviation from the darwin design (different sizes) and thus recalculating a lot of the work that is done by Ed Sells, which could result in other issues. Bear in mind, we've never build one of these things before - or anything for that matter ;-)
Regarding the friction, I found that using a hollow aluminium tube (10mm outer diam, 8mm inner) and some vaseline works great as a "sliding bearing". It increases the surface and fits nicely around the 8mm bars.
edit: forget the part about the sliding bearing - it does not work very well. Tolerances make it stick to easy. Also, some oil works better then vaseline.
Also, in the moving wood parts (ie Z studding ties) it protects against wear. For the carriage, I used some old 8mm (bronze) bearings from a scanner and sanded the rods lightly to prevent sticking.
edit: this is still true... as long as there is no horizontal movement but only rotation
The only concern I have right now is the accuracy of the holes in the wood blocks, specifically regarding the Z studs moving the table. We will try to put that together today and see how/if it works.
Anyway, good luck - and if we can help, let us know.
Joost
I have also looked at tubes (had som 12mm lying around, easier to saw than stainless steel, smaller sizes might be too bendy) but this would also mean deviation from the darwin design (different sizes) and thus recalculating a lot of the work that is done by Ed Sells, which could result in other issues. Bear in mind, we've never build one of these things before - or anything for that matter ;-)
Regarding the friction, I found that using a hollow aluminium tube (10mm outer diam, 8mm inner) and some vaseline works great as a "sliding bearing". It increases the surface and fits nicely around the 8mm bars.
edit: forget the part about the sliding bearing - it does not work very well. Tolerances make it stick to easy. Also, some oil works better then vaseline.
Also, in the moving wood parts (ie Z studding ties) it protects against wear. For the carriage, I used some old 8mm (bronze) bearings from a scanner and sanded the rods lightly to prevent sticking.
edit: this is still true... as long as there is no horizontal movement but only rotation
The only concern I have right now is the accuracy of the holes in the wood blocks, specifically regarding the Z studs moving the table. We will try to put that together today and see how/if it works.
Anyway, good luck - and if we can help, let us know.
Joost