Asymmetric prints

[Nicolinux 283]

Hi,

I have just finished building my Ultimaker and after printing the obligatory Ultimaker Robot, I tried another small print (trilobite - thing:28259). I didn't touch any settings (except setting the layer height to 0.2). The print seems asymmetric and skewed to the left side. The left "fishbones" are thicker towards the tip. What could be the cause? The object was positioned in parallel to the front of the machine so it seems to be related to the y axis.

Or maybe it is a bed leveling issue (although I leveled the bed right after finishing the build).

Images:

http://www.flickr.com/photos/nic0linux/9549271568/in/photostream/

http://www.flickr.com/photos/nic0linux/9546481407/

Ultimaker Robot:

http://www.flickr.com/photos/nic0linux/9546480545/

Thanks,

Stefan

 

[nick-foley 4]

Loose pulleys, probably the hard to access ones on the short belts in the back of the machine.

 

[Nicolinux 283]

I double checked all pulleys and they are not loose. In fact I had trouble loosening because I had tightened the hell out of them before.

 

[codemaven 0]

Are your motors pushed down as far as you can get them to tension up the short pullys? As Nick said, this is usually caused by one of the short pullys being loose. If the motor screws are not tight enough the motors can creep up and loosen those belts on you.

Cheers,

Troy.

 

[nick-foley 4]

I would also make 100% sure that there isn't any aluminum swarf stuck in the bottom of the threaded pulley holes. No matter how hard you tighten the screws, if there is material down there, the pulleys will slide.

 

[illuminarti 16]

Looks like backlash causing positional inaccuracy. Check the belt tensions - especially the short ones.

[Nicolinux 283]

@CodeMaven and illuminarti: Alright, I guess that was it. I followed the advice from the wiki and didn't overdo the tightening of the motor. Well I guess sometimes it is ok to overdo it. I pushed the motor(s) down and tightened the four screws. To be honest - I don't like this approach. Over screw holes will wear out and will allow for more and more play. I am thinking about another approach. Maybe something involving a small bearing that pushes against the short belts from the side. The position of the bearing should be adjustable so one can control the amount of pressure that is exerted on the belt. What do you think? I know about thing:34785 - maybe this is a better solution because it protects the panel from "abusive screwing".

@Nick: I had already disassembled the x/y rods and pulleys two times in a row. I guess/hope that everything that was stuck in the pulleys would have fallen off by now.

 

[SandervG 1,096]

I have my Ultimaker for almost over a year and it has been used quite a lot.

I never had issues with motors getting loose very easy, or screw holes wearing off.

I do have washers under the screws, maybe that is a good idea if you don't have it already.

Except for the previous mentioned tips, you could also have checked your axis for alignment.

If it would be off, or the pulleys would not be parallel with the axis, this could also create more resistant when

the printhead will approach the frame/sides.

 

[Nicolinux 283]

I have washers on the outside and the inside of the panel (and since I used the short motor screws I had to shorten the plastic spacers - stupid idea, I could have used longer screws instead but I didn't know how many screws would be left over). I have also checked the axis alignment - it is alright (according to the provided "measurement sticks").

 

[codemaven 0]

I've had my Ultimaker for over 2 years now... Way back when I got it I had this problem with the short belts... But once I moved the motors and tightened the screws I never had an issue after that. You don't have to force the screws until they strip, but just make sure that they are nice and (hand) tight. Do not use an electric screwdriver or anything like that. Once they're on there good they will not slip.

Cheers,

Troy.

 

[Nicolinux 283]

Alright, thanks CodeMaven. The motors are tight and I won't bother them for now. I have aligned the aligned the axis (again and again) and tightened the pulleys down.

One more issue to go and I hope I will finally start to get decent prints:

http://umforum.ultimaker.com/index.php?/topic/2716-cannot-lower-bed-to-reach-endstop

 

[gr5 1,072]

ws I had to shorten the plastic spacers

 

oh no! Don't do that. Too late I guess. Those spacers aren't long enough as it is. I had to add washers under them because the X stepper short belt was hitting the back of the UM.

Please watch your printer while it is printing and look at the short belts. Especially the X belt. If it is hitting the wood it is really hard to tell. You can tell this is happening because the belt kind of twists - and it twists a different direction each time the X stepper changes direction. If this is happening you need to add more washers (and possibly longer screws?).

You could potentially throw away the plastic spacers and use the wooden ones instead. The only downside is your UM will be much more noisy.

My screws just barely reach the X motor. I didn't try longer ones.

 

[Nicolinux 283]

Thanks for the warning. I made sure that the short belt doesn't touch the wooden panel. That's why I didn't follow the advice from the assembly instructions and placed the pulley quite close to the motor.