Banding question

I am building my next generation of R2 compatible printer using an R2 to print the parts. The next generation uses the same print head I use on the R2. The frame is made out of EU3030 extrusions. The part shown is the upper left corner. Printed in GST3D clear plastic and weighing 480 grams. Clear plastic with no color additives "should" be strongest.

The banding that is visible is the 2mm belt spacing. It is both the x and y directions and can not be felt. If it was an opaque plastic it would not be visible. I can not figure out the cause of visible banding with no corresponding dimensional change.

More info: On a different R2 I am using the same plastic. There are two straight runs of different lengths. The banding is ever so slightly different in length, like a vernier scale on calipers.

Could this be a rounding error. Could calculations be to more digits than what is loaded into the stepper timer resulting in a periodic change of 1 bit causing more then less filament to be fed. Could a one bit change cause a visible change in density?

Any ideas? Any way to define a test? I will try and do the math for how many bits must be loaded into the extruder stepper timer. I am feeding at 55 mm/sec, 141.2 steps per mm.

 

I want to know what is causing the visibility. I am never happy until I figure out why something does what it does. I pulled the 141 steps/mm right out of the eeprom which takes into account the 16 micro steps I use. Since I am making 4 corners and the second corner is now printing, I will make the 3rd corner micro step at 32. The part is all straight lines so the processor should be able to keep up. If the banding changes we will know it is round off error.

My next corner finished. I changed my x,y drivers to the DVR8825 fast mod and I changed to to 32 steps from 16 steps. Absolutely no change in the banding. The holes have radial banding emanating from the center of the hole that look like the Japanese flag.

This must be either a slicer or a math problem.