Banding Issue

[JLeithauser]

I have a Robo3D R1 with the hex hotend and I'm having an issue with the sides of my prints not being smooth (see picture).

I've looked through the troubleshooting guide and the images they have show individual layers not aligning with the others, this looks more wavy and consistent and it's groups of layers (approx. 3-6 depending on layer height).

I also looked into a number of the possible issues with the troubleshooting guide and I've not been able to get rid of the lines. The temperature is generally pretty stable, within +/- .5 degrees C so I don't believe that's an issue and the thermistor is held in with a set screw so I know it's making good contact (I had an issue at one point where the temperatures would vary beyond the cut-off and the prints would randomly fail right in the middle).

The material I'm currently using is well within tolerance and doesn't vary hardly at all. The bed is held pretty firmly in place with recessed magnets in bores tight enough to locate on the magnet outside diameters and it doesn't move during printing as near as I can tell (aside from the y-axis movement for those not familiar with the platform).

The Z-axis screws look straight and I've made sure they're lubricated with a light oil, when I remove the carriage assembly the guides thread easily along the entire length of the screws so I don't see how that would be a problem.

I calibrated the extruder (it was under-extruding by about 15mm) so it should be getting the right amount of material there. I just got a new nozzle to print with CF reinforced materials so there's no jamming issue.

The only thing that sticks out to me is I have the extrusion width set lower than the nozzle diameter (.34 vs. .4 nozzle), the reason being is that I've had issues with the perimeters not making contact and bonding to each other with the standard width. I tried slowing the x/y movement speed (went from 3600 to 1200mm/min in increments) but it didn't seem to change anything and it was getting to the point where it was estimating several hours for a very small test part (2.5L X .5W x .2H). I stopped a print mid-cycle and measured the width of one of the wall paths and set it to .5mm wider than what I measured. That seemed to take care of the outer layers not adhering to each other but it didn't seem to affect the banding issue.

I've seen others having banding issues but, again, it's usually only one layer every couple or it's only in a certain area on the print (specific sides, after a certain height, etc...). I've played with the extrusion rate and print speed settings with very limited success during test builds, I'm just not sure what to try next.

[MasterFX]

Dude you should use some line breaks in your text. It is very hard to read...
For me it looks like you threaded rod of your z-axis is wobbling... did you checked that?
Also check you belt tension

[JLeithauser]

Sorry for the big block of text. I dont do much posting online, I'll keep that in mind.

As far as the z-axis wobble is concerned, the threaded rod, at least on one side does move a bit on quick inspection, good call. I'll see if i can fix that and post back if it helps.

The tension on the belts seems fine, i dont think it's that. The threaded rod seems much more likely at this point.

Thanks for the input.

[JLeithauser]

So the z-axis screw wobble seems to have been the culprit. I mechanically adjusted the couplings to remove as much of the wobble as possible and the bands are pretty much all gone. There's a little bit of it still visible in certain features but overall the surface finish on perimeters is worlds better.

Thanks for the help.