Fun With Cylinders
I was wondering if printing some single walled cylinders could lead to any enlightenment in the quest for perfect circles and generally better calibration, so I tried the experiment, and here is the first example with default settings:
My circles looked pretty good after installing the Y Belt Tension gadget, but if you look at the above images (all the same cylinder rotated to different positions), you can see a place where the reflection gets wider for a flat spot, then narrows down for a sharper bend. So one thing printing cylinders does is allow you to see and be irritated by defects you might otherwise miss :-).
The other obvious thing you can see is a line of blobs that follows around the point where the layer changed. Why is it spiral? I wondered that too, so I started playing with settings, and I found the Wipe while retracting checkbox in the extruder page of the printer settings. If I turn that off, I get this for a cylinder:
A simple line of blobs instead of a spiral. There is also a place near the top where the line jogs back a forth a tiny bit. Perhaps my bed stabilizer runs into something at that level? The moire effect so obvious in the first pic is considerably reduced in this one, but that's probably just because the extruder pulses all line up exactly the same on every layer.
I went on to print lots of other cylinders, but none of them are really worth showing, because they all came out just like these (or worse):
- Increased retraction and retraction speed - no change.
- Set Extra length on restart to a small negative number - blobs just as big, but layer right after the blob printed too thin.
- Decreased hot end temp - no change in blobs, but if temp got too low, it couldn't extrude fully and the wall came out thin in spots.
I think I'm going to call this the “Chipmunk Effect”. I still have the stock Solidoodle hot end with the flexible PEEK barrel on it. I think it just stores up lots of molten filament in its cheeks like a chipmunk, and the retraction has no effect.
I do have an E3D hot end I got to have a backup in case anything went wrong, so maybe I'll install it someday and see if the all metal infinitely less chipmunk-line barrel works better :-).
One theory I have is that I could edit the gcode to do the retraction slightly before it stops moving so the blob would just come out as a more normal part of the wall, but that could get tricky to tune or automate (though perhaps a perl script just for the gcode of my cylinder would be possible).
I've now installed the direct Y drive, and the results are pretty impressive. Here's a video of the first test cylinder I printed following the mod:
