Hello,
I am new in this forum and I am wandering if not all UM enthusiast has been thinking to build a larger printer after having the UM original. Having a mechanical engineer background, I was thinking to design and build a 900 x 900 x 900 useful volume 3d printer for a special project I have in mind since years. The mechanical part of that machine present several challenges but I am confident they can be handled somehow. My problem is the modifications needed in the electronics and control program for the step motors. By now I have made only sketches and a brief study of the structure, the x, y and z axis, but before to go further in details I would like to have your expert opinion concerning the following topics:
1. The printing bed would be a large piece of glass, 1000 x 1000 x 12 mm approximately, having a mass of about 30 kg, let's say 33 kg with an special support. I am planning to use two lead screws of 10 mm with a pitch of 3 mm and four 20 mm diameter rods as guiding. In this way two step motors Nema 17 could handle the weight with a torque of about 0.145 Nm each, lifting the bed and 0.043 Nm going down. (Holding torque is 0.44 Nm according to the motor specifications).
Would I need to change the step motor driver ? Or the original driver can handle the current since most the time gravity help me a lot and in any case I can lift by hand the printed bed once the printed model is finished. Very short time is used to send the printing bed to home during its level adjustment, so hopefully the driver can support that current briefly.
Another question, is it absolutely necessary to link mechanically the step motors to synchronize them or the electronics are in charge of this task. Is it safe enough ?
2. The pulley for driving the x and y axis would be bigger than the original. This creates problems with the speed and exact positioning of the printer head. For example, using a preliminary arrangement, if the model ask for a 100 mm displacement, the print head will travel about 146 mm and at higher speed than the program "thinks", this would force me to change the feeding rate of the PLA filament.
Although I can modify the gear ratio in the extruder, is there another way to modify the parameters in the control program to adjust the accuracy of the movement and the feeding rate as needed? How to do it ? I am completely new to such things, but I do not care if I have to study something new, so some hints would be appreciated.
3. Printing head is moving on a gantry rail using a very large toothed belt fixed to the structure as well as the driving motor. This increase the weight of the moving parts compared to the original arrangement so I think I should reduce the maximum travel speed about 150 mm/s despite of the longer printing time. On the other hand this increase in weight is rewarded with a gantry deflection of about 0.04 mm in worst case. I have to study more in detail this subject.
What would be the best toothed belt profile to use? By now I have study this subject using a AT5 profile but probably for this application it is not the best option.
4. Other points that I have to take in consideration?
Hopping to hear from you soon I wish you Merry Christmas and the best for the incoming new year
Rafael