I finished assembling my printer and actually got it printing…but only for a short while. Before I get into what I learned and the problems I encountered, here are are some in-progress photos of the build.
First is the base with the stepper motors mounted and the spools wrapped with the Spectra fishing line:
Assembly is nearing completion. Still to be installed are two of the carriages, the hot end effector and rods, the extruder, and the end stops. At this point the wiring looks pretty neat—but that changed later once I had all the wiring in place.
I ended up designing a new hot end mount. This is made from two halves that bolt together and clamp both the hot end and the pneumatic fitting securely in place. The two-part mount is easier to make because it requires less precision than if you needed tight-fitting holes.
And the fully assembled printer:
You can see from the last photo that there are wires all over the place. I discovered I didn’t have any place where I could use zip ties to hold the wires in place. Something I’ll fix with in the next version.
For the extruder, I downloaded RichRap’s 3DR files and built the extruder without any modifications. I was able to reuse most of the extruder hardware from my Printrbot Simple.
My main problem was with the Spectra spools attached to the stepper motors. First, the set screws kept coming loose and falling out. So it would print fine for a while, and then start to do odd things because one of the spools had come loose. Tightening the screws was also difficult because they were hard to get to. And when I did get the screws tight again, sometimes the spool was a little off axis, which then caused it to rub against the base piece, and therefore not move correctly.
After fighting the spool problems, I decided I could either make new spools that were shorter. Or I could modify the base pieces to provide more clearance between the spools and the base.
I also discovered that I couldn’t use the full 170mm diameter of the print area. When I asked on the RepRap forums, I found out that others plan for about 110mm as the usable diameter for printing. Hmmm. In looking at the Kossel Mini, I noticed the extrusions were quite a bit farther away from the center bed.
Finally, the entire printer wasn’t quite as sturdy as I would like. I could wiggle the top of the printer back and forth too easily for my liking.
So with all of these problems, I decided to start on version 2.
First I tackled the sturdiness. In my original design, each part had three walls and one row of screws. Adding the fourth wall and a second row of screws made the assembly much stiffer than the old design. Here you can see a test with a new set of parts.
Next I extended each wing section (the green and yellow below) by 20mm. This increased the side-to-side distance between the extrusions by 40mm, which will allow a larger print area. The printable diameter increases by about 35mm, so I should end up with a useable print diameter of about 145mm, which is about the same as the printable height.
I also modified the base parts that hold the stepper motors to provide much more clearance between the spool and the base (can’t really see here). And I redesigned the upper parts so each one has a slot for zip ties that will help hold the wires in place.
Right now I’m busy printing a new set of parts, and we’ll see how the new design turns out.