I had few issues with my old X-axis. When I built it, I didn’t entirely understand how to constrain it without it binding up. As a result, there was lots of extra friction in the Y-axis motion, which limited my printing speed. To compensate for this I had to add extra play in a few of the guide holes. I also had to add extra play to account for my poor tolerances in building the wood parts. In general, the weight of the extruder hanging off one side of the X-axis helps to deal with play. I was still not happy with how much I could move the head around without turning the steppers.
In addition to that, I had a problem securing the X-axis rods with set screws tapped into MDF. That wasn’t a very good idea in the first place and I had been hoping that everything held together long enough for me to print replacements. It all came apart one day when, during a print, one of the X-axis rods slid out of position and dropped the head onto the work piece. I wasn’t watching at the time. The combination of the stepper yanking the now unconstrained head around and the hot tip drilled through the part and messed up the work surface. It wasn’t pretty. I reassembled everything and I added hose clamps to trap the X-axis rods and prevent a repeat. This hack wasn’t pretty. The X-axis rods vibrate a lot and the new metal on metal parts made a lot of noise.
I also had a noise where the plywood base for my extruder contacted the MDF carriage. It would seem plywood is an excellent sound board. Anything I can do to dampen the vibrations going into that will be a plus.
So, I decided to print new parts for my X-axis. They would be more precise and so have less play. They would have the proper Y-axis 3-point constraint and so I could move faster. They would be plastic parts that would not resonate with my wood parts. The set screws would be held in place by trapped nuts. In addition, this would give me a chance to dogfood my system before printing Mendel parts to give to someone else. That would turn out to be important.
The printed parts are not all printed in the same orientation that they are mounted. When I rotated one part to connect to another, I noticed some holes that were mismatched. In particular, it appeared the Z-axis in the printing orientation was shorter than the X and Y axis. I reviewed my firmware parameters and recalculated the z steps per mm setting. It was set to 150, but I calculated it to be 160. That explained the discrepency. I also checked the x and y steps per mm settings. These were set to 10, but I calculated 9.85 as the correct value. So, x and y were slightly too large and z was significantly too small. On the small calibration parts I had printed before, the measurement was close enough that I wasn’t sure if what I was seeing was just errors from the raft, perimeter width and loose guides.
After I replaced the X-axis I tested the X and Y motion without the extruder mounted to make sure everything was working fine. I was surprised that it wasn’t much quieter than before. I was relieved later when I put the extruder on and the X and Y motion became much quieter. It seems that a little mass is required to make the steppers run smoothly.
The biggest play issue I observed with the old X axis was that the carriage would rotate around the X axis, lifting the head up off from the bed. There was a lot of play in the carriage guides. The new X axis does not have that play, but unfortunately it still rotates around the X axis. This appears to be because the 8 mm steel rods that hold it bend a little bit.
I printed a Mendel part after I changed the X axis and adjusted the step distances. The texture on the sides looks a little better than previous things I’ve printed. I discovered while printing this part that the layer thickness was now too high leading to a lower density infill than expected. That is because I setup all the Skeinforge properties using the incorrect z step size. Now I have to adjust it for the corrected values. I’m printing a second part now with different Skeinforge settings and it is looking very good so far.