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Fast leadscrew design

Posted by anvoice 
Fast leadscrew design
November 14, 2014 02:16AM
Hello everyone,

I'm designing a printer (right, who isn't?) and plan to base it on fast lead screws for x and y axes. Parts are arriving now, so I'll start construction shortly. Here's some preliminary details:

Main distinguishing characteristics:
- Use of fast lead screws for X and Y
- Fairly large build volume of around 360 x 360 x 400 mm (x, y, z)
- Heated bed to support wide range of printing materials, most likely 2 extruders for added capabilities

Ill be using a V-slot aluminum frame that's so popular recently, which doubles as a linear guide and will avoid putting excessive stress on the lead screws. The larger silicone heated bed requires a fair bit of power (350-450W) so I chose to use a 24V 30A psu which should leave me with plenty to power everything else. The higher voltage should also help motor performance, not to mention heating speed. Currently have some ~50 Nm Nema17 motors on hand so will be using those for the axes, unless it turns out I need more power for the size of the printer.

It's basically a learning experience as well as an attempt at making improvements over existing designs, and will serve as a modular testing platform for new ideas in the future. I plan to share my progress with you guys if anyone is interested, and I'd be happy to hear your feedback and suggestions, as well as design ideas along the way.
Re: Fast leadscrew design
December 21, 2014 09:33PM
I'm interested already! With the fast leadscrews, are you using a single fast nut for each axis? I've been in machine design for a while, and there are several things I think of immediately;

1) Using a single nut will have a lot of backlash

2) Using a single nut will have a lot of wear, which will increase backlash over time

3) Use two nuts, preferably with a very wear resistant and low friction material (like PTFE filled acetal) that are adjusted for near-zero backlash

4) Fast leadscrews have a higher pitch angle, which means they apply more torque to the nut when turning. This can twist the carriages if they aren't ultra rigid

5) The NEMA17s are good, but they may end up limiting your maximum acceleration. If you can't accelerate at at least 1500mm/s^2, upgrade to NEMA 23s.

More specific to printing;

1) Use a hotend that can't melt and has nozzles close together.
2) Bowden tubes are the way to go if you want faster accelerations and overall faster prints.
3) Use an aluminum heat spreader plate with a sheet of PEI on it. Big benefits!
4) If you enclose it (which you really should) use polycarbonate windows and make sure that all the parts in the hot zone are heat resistant and non-flammable.

Good luck on this build, make sure you keep us updated here!
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