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University RepRap project (inputs wanted)!

Posted by signedtu 
University RepRap project (inputs wanted)!
March 22, 2021 05:08AM
Dear fellow RepRap-enthusiasts

We are a group of students from The Technical University of Denmark who are currently working on a CNC mill RepRap project. Our goal is to build a strong mini mill for precision mechanics in steel.
We are only 6 weeks into the project and would love to hear your input.

Would you be interested in buying a starter kit including all parts needed to fully assemble and use the mill? The software, drawings and bill of materials would of course also be freely available if you are not interested in the starter kit.

For software we have chosen GRBL to convert G-code to our Arduino Uno.
Do you consider Arduino to be a good platform for a mini CNC-mill and do you have any thoughts on GRBL?

For stabilizing, would you prefer the use of linear beams with built in dove tails and matching negatives or would you rather prefer using threaded rods with assisting linear rods?

Where would you prefer to place the degrees of freedom?

If you have any good advice, please feel free to tell us.
You are also welcome to contact Tor via mail s194467@student.dtu.dk

Best regards Jakob, Tor, Frederik, Christian and Signe

(We will update this thread continuously)
Re: University RepRap project (inputs wanted)!
March 22, 2021 05:49AM
... a good idea could be to read through the CNC-milling sub-forum (if not done already):


Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]
Re: University RepRap project (inputs wanted)!
March 22, 2021 09:40PM
If you're building from steel with rigidity in mind (actually be able to machine something other than plastic without resonance) source ball screws and linear motion guides (at least on x and y) from ebay. This will save time in construction. They can be had for 5-10% of normal cost and will help ensure success and a higher quality part. Theres a seller in S Korea that deals in surplus and has excellent quality and you will have your package in a few days (always amazed when I get a package from him 3k miles away in 3 days).
Dovetails are a good way to go but have significant drag the motors will have to overcome. This usually means slower rapids and overall lower efficiency and require bigger motors and bigger everything. The cost balances somewhat. Same with lead screws and anti backlash nuts= low efficiency. 5-10 mm lead ball screws will give excellent thrust force
with nema 23 steppers or even nema 17. Regular old 8 bit board
with grbl and adequate sized drivers will do as the required step rate will be pretty low. Run the highest voltage to the motors (and/or drivers) can take and you can afford. For the motors use 32 * √L = max stepper voltage where L is the motor inductance. Back off the the next lower nominal voltage for good measure.

Edited 1 time(s). Last edit at 03/22/2021 09:43PM by Bill Clark.
Re: University RepRap project (inputs wanted)!
March 23, 2021 05:20PM
Take a look at the grblHal project for running grbl on a Teensy 4.1. I think you'll find it much better than grbl on an Uno.
Re: University RepRap project (inputs wanted)!
March 24, 2021 06:03AM
Thank you so much for your feedback! It has given us a lot to consider.
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