After my struggle with trying to level the upper frame I decided to design some adjustment screws. I used 1/4-20 threaded rod and some strips of steel. I wanted to make a template that I could lay over my steel strip stock to easily layout the holes. I tried just printing the drawing at 1:1 scale with 100% zoom, but my printed image was off by quite a bit. The 1.5″ dimension became 1.636″.
I found out what zoom % I would need and then tried printing again. I was able to get within about 0.001″ (as best as I can tell measuring the printed line). One problem with adjusting the zoom level in the printing dialog is that you can only round to the nearest percentage. I then realized I could just print at 100% but put my scale factor in the User Defined drawing scale in SolidWorks.
With my templates in hand, it was fairly quick work cutting some 3/4 x 1/8″ steel strip with a cutoff wheel on my angle grinder and then marking the hole locations with a center punch. I then used progressively larger drill bits to open the holes with a hand drill.
I cut the threaded rod to size with an angle grinder as well. I used a bench grinder to clean up the cut end a bit, then used a Dremel to touch up the start of the thread.
I joined the steel brackets to the rod with some 1/4-20 nuts and to the frame with some M5 screws and T-nuts. I had to slide the legs inboard a bit to keep the adjustment screws outboard, but that wasn’t much trouble.
Next I worked on making my belt clamps for the Y-Axis. The clamps use an M5 screw, nuts, and a T-nut to adjust the tension. Grooves on the top hold the teeth of the belt to less clamping pressure is required (and less belt damage). I also made a non-adjustable version for the back end.
To cut the aluminum angle I placed it corner up on the miter saw. I didn’t like the idea of the saw hitting a thin leg that was facing up at a right angle. I used two shims under some hex keys stuck in the fence to apply clamping pressure. The cuts came out clean, but the last bit of the corner wasn’t quite cut, closest to the base of the saw.
I moved the aluminum angle out a bit from the fence using some vice parallels and this cleaned things up.
I used the same template layout method that I used with the steel strips. This time I had two templates, one for the top and one for the front of the bracket. To mark the grooves, I used a center punch in their lower right hand corners, then laid out lines as guides.
I tapped the holes on the top for 10-32 screws. Grooves were cut with a Dremel cut-off wheel.
Some grooves are cut better than others, but the clamps hold quite well and don’t seem to damage the belts.
After I was cleaning up from this job, I found out that my tapping could have been much easier if I realized what my handy tap holder was capable of. I was wondering what this little bar sticking out if it was for, then realized that it was a switch that selected between ratcheting in, ratcheting out, and locking in place. My next tap jobs will go much faster.
Next I built up the XZ Carriage assembly, leaving the bottom wheels off so I can drop it onto the X-Axis track.
I put this carriage on the extrusion and tightened it up. Unfortunately there was quite a lot of flex. It was rotating about the X-axis so that with modest pressure there was almost a quarter inch deflection at the tip.
Looking more closely it appeared that the problem was deflection between the inner and outer races of the ball bearings. If you look closely you can see the plastic wheel and bearings stay still while the screw and other components move along the screw’s length.
I didn’t want to work with different wheels and bearings so it was time to go back to the drawing board and see how to stiffen things up, maybe with an extra row of wheels. While I was in the garage though, I thought I’d give my stepper motors a real-life test for the Y-axis with my newly installed belts and clamps. This led to more problems. Using Sprinter firmware and Pronterface I was able to at about 5000 mm/min in the positive Y quite repeatably. At this point I was using two NEMA 23 motors driven with a single Pololu stepper and this mess of recycled ATX power supply wire.
One of the steppers had the coil polarity reversed so that it would step in the opposite direction.
Things seemed to be ok for slow speeds in both directions, but once I started creeping up to even modest speeds I would loose steps while moving in the -Y. I tried increasing the current on my stepper driver, but that didn’t seem to help. In fact, when I got to about 3/4 current level, my steppers started to flutter like bumble bees; not wanting to remain in one place. I did have a heat sink on the driver chip and plenty of air flow. The chip was cool to touch during the whole process. My suspicions right now are:
- Long and messy wiring is inviting the chance for inductance loops.
- The coil resistance of these steppers is not what the driver was meant to handle (TBD).
- While two NEMA17 motors may be driven by most 3D printers at slow speeds for Z, it may not follow that two NEMA23 motors may be driven by my machine at faster Y speeds. (This may require separate chips that share step, direction, and enable signals.)
- My firmware may not be configured properly (acceleration ramps, etc).
- I may have unrealistic expectations for how fast any one axis should be able to move.
The project is starting to look like a machine though:
