From my first few prints, I noticed that some vertical walls in the parts were not perfectly planar. The image below is a good example of this. This is the result of the nozzle not returning to the exact same X and Y coordinate on every layer.
Since I had anti-backlash nuts on the ACME screws, lead screw backlash was not the problem. The problem I found was that the X and Y stepper motors were being run too fast and were thus skipping steps. This resulted in the X and Y axes not returning to the same exact position on each layer, hence the above image. After some speed calibration, I resolved this by setting the motors’ max speed at a point where they would not skip any steps. This max speed was set in Skeinforge. Unfortunately with Skeinforge, it sets all axes to this max speed. The Z axis needs to move much slower than the X and Y because it has to lift the entire Z stage. You can set a max speed in the machines.xml file in ReplicatorG, but it does not seem to obey this on its own. A M105 command needs to be inserted at the beginning of every g-code file, which prevents the motors from exceeding the max speed that is set in machines.xml.
3/8"-8 2 Start ACME lead screw
3/8″-12 ACME screw is a little slow, only traveling .083in [2.11mm] per motor revolution. I decided to change the X and Y axes to 3/8-8 2-start ACME screws which provides travel of .25in [6.35] per motor revolution, significantly increasing print speed. Now I run my machine at 20 mm/s in the X and Y axes, and 5 mm/s in the Z axis.
If you use Skeinforge directly you can set the Z limit in the Carve – Limit plugin under “Maximum Z Feed Rate (mm/s)”.
Yes, I have been using the version of Skeinforge that is bundled with ReplicatorG. It is missing a number of input fields as compared to the standalone and other versions.