Hi All,
This actually started in a thread where I asked for advice specifically on stepper motor choice. However the discussion evolved in to more general details of the machine so I'm moving the chat over here. I'd welcome constructive input. Although I have already purchased most of the drive parts, I have still to build the frame and assemble it.
So far this is my design. Over-all size is about 550mm^3.
Frame is welded 40x40mm steel with concrete and SBR (latex) admixture core for damping.
1mm Steel panelling (not pictured) welded on all sides for bracing except front and top.
Gantry is 30x30mm two aluminium tubes with a constrained (layer damping) PU core.
16mm dia. 20mm pitch ball-screws with 4-start thread.
MGN 12mm profile linear rails on X and Y.
X and Y drive is Nema 23 Leadshine 57CM13 with 60V TMC2160 drivers.
Bed is 10mm or maybe 16mm cast ali tool plate, face machined for flatness.
Z rails are 16mm round rail with ball-bearing slide blocks.
Z drive is dual Nema 17 0.42Nm with integrated T8 lead-screw.
Attachment 443732
I'll respond to a few existing questions below.
One rotation produces 20mm linear travel. However there are 4 threads wrapped around each other. Visually it looks like a 1605 ballscrew but it's not quite. I didn't spec it like that, but that's how it came! AFAIK it just means there are more balls in the nut for support and redundancy. I'm not sure if it improves backlash??Originally Posted by joeavaerage
The Z axis uses ball-bearing bushes. So stick-slip I hope won't be an issue. 3D printers don't need to handle any cutting forces or significant weight on the z-axis so 'surface-on-surface' ways or oiled bushings are not commonly used unlike in mills or presses. Many printers only support the print surface on one edge! Horrible IMO.Originally Posted by peteeng
Attachment 443734
That's interesting to know. I was going to use concrete with SBR which is a latex addative used to improve damping (and water-proof) in concrete structures. I got the idea from here - https://www.researchgate.net/publica...city_of_cementOriginally Posted by peteeng
This paper 'Principles of Rapid Machine Design' is super informative on damping beams (see captor 4).
Although it is investigating layer damping, it does mention the loss factor of polymer concrete.
Attachment 443738
If, as you say the internal damping of the concrete makes little difference when cast inside a steel beam, so be it. Maybe I can through some damping sheets in there with the concrete to constrain the damping sheet. However I'm conscious of how practical it will be to add the damping materials to the frame once constructed. Capping off the ends and pouring is pretty easy, but individually adding damping to each beam before welding sounds tricky.
I actually work mainly in acoustics, so have the means to measure and test damping and make comparisons. Maybe I will do a small test run to compare basic concrete fill vs. concrete with SBR addative (and possibly 10mm granite gravel?)