Slanty Cubes!

I just finished building my Prusa and have been printing cubes for about two days now. The prints are very reliable, i.e. I have the same kind of problems each print. I was wondering if you all could help me out with solving my print problems.

My Setups:
SAE Prusa
Wade's Extruder
Custom Gen6 Electronics
Green ABS PLA printing at 238 C

I have a few problems, but the largest one is that the Z axis seems to shift towards the right as it goes up during a print. The cubes are indeed 20mm x 20mm x10mm (as they should be), but it is almost like the leaning tower of Pisa. The I have quadruple checked that the frame is correctly alighted with itself, and it is! I have tried miss-aligning the Z-axis to fix the problem, yet the problem does not resolve itself. I saw in another post that the problem was from the filament pulling on the X-axis causing it to skip steps, but this is definitely not the cause in my situation.

A few other things that might be pertinent. I have been very confused with the E_STEPS_PER_MM parameter. My number seems to be WAY too high. The default for the Gen6 firmware is 20.2, but that is not for my extruder nor SAE. I did a test with Repsnapper to determine my value. I set the speed to about 1000, and set the length to 500. The filament moved less than 2cm. I then set the E_STEPS_PER_MM to 50. I feel like this value is too high, and I worry that the extruder is slipping every now and then (even though I dont hear or see anything). The tilt on the Z axis seemed to be slightly less with this value set higher. Using the calculator, it gave me a step value of 64!

Once I fix this I can start printing upgrades and learn Skeinforge better! I really am at a loss with the settings in Skeinforge, but I don't want to delve into it until I can print a reasonably "perfect" cube.

Does anyone have any idea what could be causing this? I have included a picture of my latest cube print.

Edited 1 time(s). Last edit at 10/07/2011 05:54PM by NJC.

looks like you might not be driving enough current for the motor in that axis. try increasing the current for that stepper during a print and see what happens.

also, take a look at this blog post from richrap: http://richrap.blogspot.com/2011/10/art-of-failure-when-3d-prints-go-wrong.html

thanks for the link! a very good read. interesting information too, I definitely will be playing more with the temperature and other settings than I thought I would.

I did try changing the power to the stepper, and it stayed the same regardless of the power I had it at. I went from where it wont move reliably because of too low power, to having it shut off because the chip gets too hot.

Since none of the other motors were having this trouble, I thought it could be too much friction on the one axis. I added some lubricant (silicone spray, since my other PTFE lube is in the mail), still printed with a slight slant.

Once the print was finished, I started to pay more attention to it moving through manual control in Repsnapper. I noticed that for some reason the sound of the motor moving is steady in one direction, but not the other. I'm going to double check tomorrow with a sound recording to be sure (it's very faint).

I have two theories, but it will take some messing with to figure out what the cause it. First idea is that it is the metal bushings that I am using on the X-axis rails, maybe its tougher to pull in one direction that the other causing it to skip a bit. My other idea is the stepper motor driver. Tomorrow I will try switching the X-axis and Y-axis to see if it is the motor driver, or the mechanics.

Has anyone seen this problem before? Any ideas? Thanks so much for the help guys.


Edit: One last thing I forgot, the X-axis quivers a bit when I turn on the printer or anytime I connect to the computer. It doesn't happen with any of the other motors and stops after 5-10 seconds, it's a bit weird considering the X-axis it the only one seemingly messing up.

Edited 2 time(s). Last edit at 10/07/2011 11:46PM by NJC.

Looks more like the pulley slipping on the motor shaft rather than skipped steps.

I expirienced a skew on both axes on my Huxley. I think it is because of high friction and overall asymmetry of my machine.
I've activated a sample skeinforge homing.gcode:
G1 X-250.0
G92 X0 ;set x 0
G1 Y-250.0
G92 Y0 ;set y 0

Now printer homes after each layer and objects come out straight.
I know it rather hides problem than resolves it and I can get problems with large and complex prints.
But, from other point of view, it doing its best using endstop feedback, I think even in best machines it is impossible to build big objects without any feedback.

Well, I think I ruled out a mechanical problem. I tested this by driving the X-axis motor with the Y-axis driver, and the Y-axis motor with the X-axis driver (I also switched the end stops). Now the slant was in the Y direction and not the X. This leads to me to believe that it is an electronics problem.

I ended up replacing the driver chip for the X-axis; this solved the twitching problem I had on startup, but the slant was still there. Now I have three ideas. The first idea is that there is something wrong with the opto end stop circuitry, the second is that the firmware is causing the problem, and the second is that the stepper driver circuit is causing the problem. I'm going to triple check everything with my multimeter, scope, and logic probes first, and then possibly try the newest sprinter firmware.

Any ideas? This is definitely a bit weird.

I am really at a loss here. I tested the opto through a run with my scope and the opto is not a problem. I upgraded the firmware to the Sprinter FW (Sprinter (the new Marlin FM from mendel-parts.com), and the problem still happens. I don't think it is the firmware.

I have double and triple checked the servo circuit and everything seems to be fine, yet I am still getting slanted prints.

How big is your filament spool? 5 pounds?

If you have a big load to pull on the filament spool (big here is relative) it can slant your prints, or make layers look uneven.

For best results, try and eliminate as much resistance to the filament feed as possible.

1. Use small spools of filament. Enough to print what you want to print.
2. Use one of the many filament spool designs on thingiverse, if you can get to the point where you can print, that is.
3. Make sure the X carriage moves freely. There should not be resistance there, at all. The more resistance, the greater the backlash, and potential for missing steps.

The spool is probably about .5 pounds at this point, and I hand fed it for a while to make sure it wasn't the spool. Plus the problem moved to the Y axis when I switched the motors.

I'm still stuck on this one, I'm probably going to rebuild the circuit soon hoping to fix it.

I hope I can figure out a solution before it comes to that.

Assuming you have heat sinks and a fan on the Pololu drivers, it could be that one of the heat sinks has come off the surface of the chip, and it is overheating, causing the over-temp protection to kick in from time to time. The other alternative cause is a bad driver. Swap the suspected bad driver with the extruder, and see what happens.

that slant is so precise, it seems to me like your z rods are not aligned. take a triangle edge, and check your alignment of your z axis rods . make sure they are perpendicular from the top of the unit, and the bottom.
even your filament lays down slightly thicker to one side.

hope it helps. that is what i think this is..

I had this problem with arduino mega + ramps. Here's what i did to fix it:

1. drill out the PLA bushings and oil the rails so the bed slides freely
2. make sure the rails are perfectly parallel
3. tighten the belt and make sure it slides freely on the bearings
4. (if you are using RAMPS) turn the potentiometer on the board clockwise to increase the current to the stepper
5. If the chip heats up too much, it will stop delivering current to the motor. correct this by getting tiny heatsinks and heatsink adhesive. If it still heats up to the point of going into protection, direct a fan toward it.
6. The belts may be too tight causing the stepper to work harder than it should have to.
7. you may have an end-stop malfunction
8. you may have a loose wiring connection
9. sometimes the setscrew in the motor pulley collides with the motor mount if it has play, fix that too.
10. early on i had to update the firmware on my arduino mega to fix it.

Hope that helps.