After calibrating the max speeds of the stepper motors, the first test print was an encoder mount that allows the RepRap magnetic rotary encoder board v1.0 to clamp onto the extruder drive motor
Encoder Mount
There are recessed spaces for a #4-40 screw and nut so the part can be clamped around the motor body. With this mount, the board is positioned exactly so the AS5040 chip is directly over the rear drive shaft. A small magnet is then attached to the rear drive shaft. (Note: These pictures display an earlier version of this part without its 4 mounting screw holes in the top for the board. The last picture in this post shows the board mounted into the final version of the part with the 4 screw mounting holes.)
Close up
The first layer is yellow because that was what color was in the heater barrel before I put the natural colored plastic in.
Backside
Mounts onto the Extruder Drive motor
It fits quite securely, and the part has a nice surface finish as well. Now the the tricky part is getting it to work with the extruder board firmware. (The above image shows the encoder board before any components were soldered.)
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.
A robust idler wheel was needed for my plastic extruder in order to withstand prolonged periods of printing. So I found some nice scrap round stock aluminum and lathe’d one up.
Newly Machined Aluminum Idler Wheel
Side View
Idler Wheel mounted into the extruder
In the above image the filament is squeezed between a knurled pulley [left] and the idler wheel [right]. The black part is the front plate of the extruder. Everything runs quite smoothly with repeatable extrusions.
