I have noticed unusual banding in the top surfaces of my prints. The bands appear at a regular interval of 11mm apart. At first I thought maybe the hobbed bolt was not feeding the filament through properly. But the bands are the same spacing no matter what I am printing. I also happen to have small sections throughout the print with missing filament. I suspect they are related issues, but don’t know for sure. Any ideas?
I’ve occasionally seen similar with prints on MakerBot’s running on my ToM and on my Replicator - my suspicion is that I may have over-packed and every so often causes an extruder drive to miss a step and create a momentary under-extrusion. Try under-extruding a hair?
That looks like a rounding error. The digital layers and the steps of the mechanics may not match, which would create a 2-step jump every specific number of steps.
I agree with @Edgar_Brown , because it’s happening on all your prints, and it’s repeating uniformly, it sounds like a gcode generation problem, not a mechanical one.
@Edgar_Brown , @Aaron_Eiche So how do I fix this? I used empirical measurements of printed parts to determine steps/mm, and used Prusa’s reprap calculator site to determine layer height based on my leadscrew. Should I try a different slicing program? I seem to remember this happening occasionally with various layer height settings (all derived from the RR calculator).
@Dante_Ranieri This happens with all of my filament regardless of the seller. I don’t think the filament is the cause in this case.
@Nathan_Withers It could simply be:
-
a matter of the surface angle, you cannot perfectly represent many lines in a discrete set of steps.
-
it is not necessarily a layer height issue, it could be X or Y travel rounding.
I would repeat the print halving the printing speed (M220 S50 if using Marlin) to check if problem goes away. If it does, it is hotend backpressure, if it does not, keep on searching.
It might be airbubbles in your fillament. Or moist in your fillament.
I agree with @Edgar_Brown , try slicing with something else and see if you get a similar artifact…
It’s so regular I suspect hobbed drive but it could be back pressure. You could mark the drive and see if the ridges always happen at same angle of rotation. Or you could go the long wash and figure out how much filament is extruded per turn and make a text piece it accentuate the problem.
Or if it’s back pressure slow down and raise temp a little.
What kind of printer is it.
Really expecting hobbed drive on this one. 11mm sounds like one of the common hob diameters. The other common one is 7mm.
I don’t think it would be rounding errors as the floating point math errors will be masked by the much higher mechanical errors
@Eric_Moy , there’s no way it’s “rounding errors” - the rounding error of a single step is way too small to cause gaps like this. The problem is definitely in the extruder mechanism somewhere down the line. This is obviously a mechanical issue as you state.
Z wobble?
Looks like a backpressure problem. Maybe bobbed bolt does not have enough grip. I would test max extruder speed and adjust accordingly.
Your gear/pulley set screw is slipping on motorshaft.
Could also be extruder motor driver overheating and stalling out.
I examined the hobbed bolt yesterday evening, and sure enough, there was some filament jambed between two teeth. I did not get a chance to do a test print before going to bed, but I am beginning to think this may have been the problem as I did not have this issue last week, and I have not changed filament or slicers.
I have had the hot end just a little too close to the print bed for the first layer for a couple weeks. I guess some filament got chewed up during a previous print and jambed in the hobbed bolt teeth.
Is it considered bad practice to make the first layer of a print more than 100% layer height rather than to spend the time truing and leveling the bed?
Has anybody implemented the automatic bed leveling use in the Kossel on a cartesian based printer? I’m using a MendelMax, and I really hate having to manually level the bed all the time.
I always make the 1st layer thicker than 100%, but I end up tweaking the flowrate in repetier host if it’s too much. I usually just allow the 1st layer to be overextruded. I get a bit of “speed bumps” during my second layer, but it ensures good bed adhesion. Then again, my prints aren’t always the greatest