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Issue with skewed printing

Posted by tophstar 
Issue with skewed printing
May 20, 2014 01:51PM
Hello all,

I own a self built Prusa Mendel i3. Sadly, while my prints are coming out looking great, they are also coming out skewed at a slight angle of about 5 degrees off of perpendicular normal of the bed. This skew is consistent, causing cubes to come out as Rhombohedrons.

So here are a few reasons I think may be causing this:
1) The y-axis is slipping/crashing. (this does not appear to be a major problem).
2) The issue may be with my z-axis. I noticed the 3M threaded z rods (not the structural smooth z rods) are skewed at an angle as well. I am using the plastic tubing (not using the metal couplers) to connect to the stepper motors, but this may be causing enough pull to cause an issue.
3) The extruder may be closer to the print bed on one end. I have tried very hard to get this distance to be as uniform as possible.

Does anyone have any other ideas? For the z-axis, how can I get the z-rods to stand perpendicular to the printer bed (perfectly parallel to the support rods)?

Best Regards,
Re: Issue with skewed printing
May 20, 2014 01:55PM
Pictures would help better identify the problem/s.

Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus
Re: Issue with skewed printing
May 20, 2014 08:50PM
Just X axis?

Case 1: it would give random results and not constant 5ยบ skew, so is not motors
Case 3: Print this! [www.thingiverse.com]

all I can think off is case 2:

your printer is not Squared. hang a pendulum or a weight and check if your Z axis has that 5 degrees skew. you can also use a set-square plastic ruler

Edited 1 time(s). Last edit at 05/20/2014 08:52PM by machapa.
Re: Issue with skewed printing
May 21, 2014 08:52PM
Well a pendulum makes obvious sense. I got the back plate a little more square with the print bed with much better results!

Thanks a bunch,
Re: Issue with skewed printing
May 31, 2014 03:36AM
I'd imagine your X and Y axis are not perpendicular. If you have a way of adjusting for one or the other, you can use a protractor to adjust and then take a piece of paper and place it on the bed while holding a pencil perpendicular to the hotend and manually making a square with the pencil to see how true things are.

I had a similar issue and was able to compensate and adjust accordingly although I'm certain it's not *perfect*.
Re: Issue with skewed printing
May 31, 2014 04:43AM
well if its your z i wouldn't worry about the threaded rod i will be something to do with the smooth rod placings

Check my rubbish blog for my prusa i3

up and running
Re: Issue with skewed printing
May 31, 2014 06:18AM
Had the same problem with mine at the start. Worked out that the z axis smooth rods needed to be adjusted out or in to compensate for the lean.

As the print travels up and away from the bed, the print head will attempt to auto-correct to true vertical in relation to the top of its travel, so if the print is leaning to the right for example, you have to adjust the bottom of the smooth z guide rods the same way to pull the print head over to start the print directly under the top centre.

The easiest print to check this as well as your other settings is a 20mm x 20mm hollow cube at 20mm high. This only used 140mm of fillament and takes 7 minutes on my settings.

I hae attached my 20x20x20 cube as stl.

Hope this helps.
open | download - 20mmcubehollow_fixed.stl (1.6 KB)
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