Fixing the Skew

Once I had the build plate levelled and sticking , I had the luxury of being a bit more methodical about diagnosing the other issues. So of course, I printed out some funky vases..

IMG_7152IMG_7156IMG_7155

..which served nothing to tell me what was wrong, but did show me that I really wasn’t going to get anything nice printed until I fixed it – there were gaps in the bottom, and the taller vase was funky on one side and almost flat on the other.

My 3D mentor friend was kind enough to whip up a few shapes for me to test on, just a couple centimeters square in area. The shapes were fairly consistently skewed, especially on the perimeter:

IMG_20130221_214843IMG_20130221_213801 IMG_20130221_205511 IMG_20130221_212623

The best diagnosis I had was that the belts were loose. It took me a ridiculously long time to figure out how to tighten the belt, so let’s see if I can explain it a bit better.. Look at the motor that drives the belt. On the MBot Cube, there’s one for the x-axis mounted on the right side and it goes back and forth. The y-axis is mounted at the back of the right side, connected by a small belt. There are four screws holding each in place. You can unscrew the motors, pull them tight against the belt (as hard as you can), and then re-tighten the screws to hold them in place.

When I tried this, things seemed to improve a little, but not completely. To see if I was on the right track, I loosened the belts. Happily, this did make it worse, specifically exaggerating the symptoms. In the example below, you can see the original prints on the left, after tightening in the top middle, and then after loosening on the left.

IMG_20130227_211209

At this point, my friend had the idea of checking the motors more specifically. Perhaps one of them wasn’t working properly? He had me go through the printer menu and enable the stepper motors. This is supposed to engage the motors and make it so that they don’t move when pushed. When I tried to move the extruder, though, the y-axis was most definitely jerking back and forth. I couldn’t see what was going on with it, so I took the entire motor off the assembly. Note: If you do this, make sure the printer’s power is off first.

Once I just had the motor with its gear in my hand, it was easy to see that the gear was not solidly attached to the motor shaft. It required the tiniest hex key to tighten it, but once that was done it wasn’t moving a bit. With everything seemingly happy, I tried a print.. and hurrah! It worked! You can see the progression of test prints here:

IMG_7158

 

  1. Default settings
  2. Tightened belts – slight improvement
  3. Loosened belts – more extreme symptoms
  4. Tightened again.. wasn’t as good as #2
  5. Tried yet again.. okay this isn’t working
  6. After fixing the motor’s gear
  7. Full solid print, dimensions almost perfectly even

 

 

Pleased with my success, I tried the meeple and lucy the cat again:

IMG_7144         IMG_7168

 

No more holes, and lucy’s back was perfect. I’m still getting a weird texture on her front.. I don’t know what’s going on there, but I’m sure there are many more settings and upgrades to look at.