Layer alignment issue

Hello everyone

I've just started printing with my RepRapPro Huxley and I'm having an issue which looks like a poor layer alignment. The strange part is that sometimes the quality is excellent but mostly not so good (check out the pictures).

Things I've already tried:
- Disconnected the belts and z-axis threaded rods and checked that all the axis are running smoothly without any play
- Upgraded the bed springs (I found richrap's post which describes a same sort of issue)
- Printed very slow at 10mm/s and decreased the acceleration to 500mm/s²
- Tightened the belts as tight as possible (currently running a bit looser though, it sounded like the stepper motors were having a hard time)
- Installed Z couplings by nophead
- Played with the extruder (175-185°C) and heatbed (45-65°C) temperatures

None of the things I've tried have shown any improvements. I print PLA and use Slic3r 0.9.7.

Any suggestions what the problem(s) may be? Could things like machined pulleys help even if the problem is somewhat random?

I'm not too familiar with the latest design of this machine but it might be worth taking a look at the carriage which moves across the X axis and carries the hot end - is there any wobble if you try and rock it at right angles to its travel? I had a similar problem which was fixed by changing the RRP design carriage with two linear bearings to one which had three linear bearings. Thingiverse thing 14793. The original files enabled the carriage too much freedom.
Alan

I have the exact same design on my machine that you referred to and it feels solid but the y carriage is a three bearing design. There's a tiny bit of wobble on the side with the single bearing. Also the carriage isn't a one-piece printed one but two separate parts connected by MDF. Should I get another linear bearing and print a new carriage? Is there a noticeable difference in final output between three and four bearing designs?

I had issues like that for a long time and replaced half my machine (prusa mendel) in the process.
What seems to finally be helping is replacing the lm8uu bearings with bushings on the x and y axes. I'm not saying this is necessarily the issue with your Huxley, but keep it in mind if all else fails.

OH - and tune the PID control for your heated bed if you have one. The auto-tune in the latest marlin firmware seems to work pretty well now.

Edited 1 time(s). Last edit at 01/13/2013 12:25AM by tsb4k.