by Jfriesen » Fri Dec 02, 2016 10:01 pm
Calibration for me mostly centered on gathering lots of accurate measurements on the actuators, and then accurately calibrating the vertical height offset from the build plate.
First I independently measured the homed lengths of each actuator and adjusted them each to be as even as possible. You can also do software trim but this is more annoying, better to just calibrate the machine. I measure this length with calipers between the two bolts when the arms are dis-assembled from the machine. Next I would use the printer board to move the arms to a shorter length, commanding 300mm shorter for instance, and then see how far I was off. I could then use these two measurements to adjust the steps per mm for each arm.
Once these are all accuratley calibrated I re-assembled the machine and sent it to the home position. I think the dome you are seeing could be caused by an incorrect vertical offset. You want to make sure that when you home the arms and measure the distance between the nozzle and the build plate that the distance there matches the readout from your machine. You also want to make sure that when you step the machine down to Z = 0 the nozzle is at the build plate height. The key here is you know the three arm lengths from previous measurements and so with one more measurement you should be able to determine the build plate height and how that needs to be adjusted.
To summarize I calibrate in this order:
-Maximum arm length for each arm (from the center point of each bolt)
-Steps per mm for each arm
-Vertical Height offset
After I get those three down I then I level the build plate manually using the adjustment screws. Perhaps I'll make a video of my calibration process. I've just been too busy! Once you get the geometry right the printer will print reasonably level (at the far outer reaches of the build volume I still see some errors around 0.5 mm in height).
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