Steps per mm
Possibly the most exciting thing for me when building a 3D printer is the electronics. I have built 2 kits (a Huxley from eMaker and a Mendel from RepRapPro) and am now building my own design. Until any printer gets attached to its electronics it is a mere metal doorstop. What I wanted to write up about was how I calculated the steps per millimetre for the DSF.
While in my usual ‘I’m bored lets search the net’ mood, I stumbled across the excellent RepRap Calculator3 by Josef Prusa. If you are building a printer from scratch this will greatly simplify figuring out what number the steps per millimetres should be.
Like many of the printers out there my DSF uses belts for the X and Y axis’ (T5) and a lead screw for the Z (M5). For the belt drives all I needed to change was the belt preset to 5mm – or the T5 belt. The pulley I was using was already 8 teeth and 1/16th stepping. As a result this would give me 80 steps per millimetre or a 0.0125mm resolution.
The Z axis uses an M5 threaded rod as its drive so again all I needed to change was the preset to M5. This means a step of 4000 steps per millimetre or 0.00025mm resolution. Obviously that is much finer then any of the prints I would ever do, the finest I have done was 0.1mm/layer. In reality I could set the stepper to full steps and still retain a resolution of 0.004mm.
So thanks to the calculators I have a 80 steps/mm for X and Y and 4000 for Z. Ignore the 800 for the extruder above. I have not yet got an extruder so that is just place holding!
One last thing; I have limited the feedrate of the Z axis to a low 2mm per second. Any faster and the motors stall. I need to oil the threaded rod to try and get some extra speed out of it, but I am not holding my breath.
So I have got the steppers installed, the electronics and endstops. Now all that was needed was to test it all together. Connection to the computer was successful and the machine came to life! The Z Axis homed the wrong way, but an update to the Marlin firmware solved this.
Simple but very effective
At the school I work at we have a RRP Mendel. I was trying to print some students work but it kept failing. Eventually I discovered that the problem was down to curling from some overhangs on one piece. As the part had 45degree angle and only 5mm thick, the printer was catching on the curled ands and eventually cause the printer to miss some steps. I needed a way of cooling the plastic faster.
I then found an 80mm computer case fan that was being recycled. As I needed to get the part printed I simply cable-tied the fan onto the smooth rods of the X-Axis. Amazingly these are about 80mm apart and the fan fitted beautifully behind the X-Axis endstop. Now I was able to get the print to finish and have a great look as well.
Time for another update. The printer is now mechanically complete. All of the motors, belts and leadscrews are all installed. I may have to adjust the X Axis motor mount eventually as it is poking a little bit too far forward, meaning that the belt wanders a bit.
I have received the Megatronics V2 electronics that I will be using on this machine, which I will try and review at a later date. Now it is just a case of installing the wiring for the motors to the electronics and sorting out the endstops. Once that is done I will see about getting it up and running to check mechanical reliability.
Now that payday has been and gone I have been able to order a few more parts for the printer. Currently the steppers have actually turned up and are installed. I had also managed to get the frog for the Y Axis laser cut with the DSF logo etched into it.
At the moment printing on my Huxley are the Z Axis couplers, pulleys for the X and Y motors and the clamps for the Y axis. I have the belt for the X and Y so once the print has finished I can hopefully get the Y axis installed and ready to go. The electronics have been ordered and should be here is 3-4 days, the psu should be with me tomorrow so once the electronics turn up I’ll get it installed and get the printer moving.
Well the main structural build is complete. All of the printed parts have been made and fitted with all the axis together. It now is starting to look like a 3D Printer! All the axis move as expected. Now I have to wait until I get money for the steppers, electronics, hotends and power supply.
Above are pictures of the printer. The first being the real build thus far and the second a 3D render of the current design.
On a side note, while I was waiting for the X Axis parts to print I designed a logo for the printer let me know what you think of it.