A few more details about the machine: The frame will be utilizing 80/20 15 series T-slot extrusions for simple and strong constructions. The linear rails will be 5/8" drill rod and the ACME screw will be a 4-start 1/2"-8 screw (2 effective threads per inch, 1/2" lead). The linear bearings will be cheap plastic sleeve bearings and the ACME nut will be a 1.5" OD flange nut that will be attached to our moving platforms. A CAD model on an early prototype is above. I'm sure the final model will look very different as this was also designed before a moving gantry was decided on.
Interesting design. How fast do you think the ACME screw will go?
ReplyDeleteWell we are hoping to use an Allegro A3982 driver for the stepper motors which has a maximum stepping frequency of 16kHz. I have accepted that the software will probably be the limiting factor and we are hoping to have an actual stepping rate close to 1kHz. At 1kHz we would be able to accomplish 150 IPM maximum speeds. The 4-start screw really speeds things up from normal threaded rod. Two rotations of the motor would move the carriage 1 inch which is very close to what darwin can accomplish with it's belt drive system. However, our axial force is MUCH larger which will allow for some light milling and other high load applications.
ReplyDeleteinteresting ... I have yet to see how well fast my ball screw system works on My big CNC build its only 5mm per rev..
ReplyDeleteThe big cnc is on hold at the moment so maybe in after the RepRap show In March I will have a bit more of a play but multiple tool heads is another thing Im looking at.
The builders manual for the Solsylva cnc has a list of the various drive types and the max ipm that each can attain. The the threaded systems seem to max out about 100 IPM. Both the belt and Rack systems are much faster.
ReplyDeleteWhile I am not familiar with the Solsylva CNC, the max speed that any CNC system can attain is dependent on the mechanical and electronic setup. Using chopper motor drivers with a much higher voltage supply (30-35V) will allow for much faster movement as well as using a multi-start leadscrew. There are screws out there that move 1" per revolution! That is very fast and comparable to belt drive systems. We are hoping to get between 150-200 IPM with our system. Also, keep in mind that we needed to design a machine that has much higher accuracy and strength than most belt drive or rank systems. PCB milling requires VERY HIGH accuracy and milling in general requires a much stronger machine than one that is intended to do just prototyping.
ReplyDeleteHello, i first want to congratulate on this project. I am interested in building a similar CNC/3d printer, what is the volume of this model? X,Y and Z travel.
ReplyDeleteThank you
Mariano