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Layers shift when printing circles.

Posted by Thingy 
Layers shift when printing circles.
August 04, 2012 03:23AM
I am quite new to this whole reprapping thiing. But as you can see on these images, the first one being the hollow cube, and the second being the better z-endstop calibrator thingie.

I did another set of couplings but they were also too slanted to use.

In the secod photo you can see how the first layers shift sideways, that is x-direction when doing circles, but when it's only straight lines it keep them straight.

I read on a blog that the pololu drivers might be at fault, so I tried adjusting the potentiometer but that made the x too hot to touch and started jittering. So I turned it down again.
I am using pronterface with the latest slic3r version. It's a sanguinololu v1.3a board with a 350W psu.

Anyone have any other idea, I could try to swap the pololu with z-axis to make sure that it's not a bad board.
I could also try to change the microsteps, I have them at 16x now.

If it were due to belt slack, wouldn't the layers shift both ways?

Hope someone have a great idea, preferable one that wont suggest buying a new stepper driver, cause I'ld hate to wait for delivery now that I am up and printing smiling smiley

Yes also I printed the cube with rectilinear infill and the z-endstop thing with honeycomb. If you think that might play into it.

Crosses thumbs for helpful input...
open | download - IMG_20120803_160515.jpg (228.2 KB)
open | download - IMG_20120804_090215.jpg (93 KB)
Re: Layers shift when printing circles.
August 04, 2012 03:44AM
You're losing steps. Swap the X and Y motor drivers and see if it stays with the X axis. If so, its probably mechanical, and over tight belt or a jammed bearing. If it moves to Y axis with the driver, then you most likely need a new driver.
Re: Layers shift when printing circles.
August 05, 2012 12:43PM
remove the belts from both x and y axes, and make sure there is no binding against the rods. Do this check by pushing each axis where it normally attaches the belt, as this point is usually off-center a bit.

The parts should move very smoothly with little or no resistance.

There are two main causes of skipping steps in the drivers current setting.

1. Current too low. The motor does not receive enough current to overcome the pull of its permanent magnets. This is the better of the two problems, as there is little chance that the driver has suffered any damage due to heat.

2. Current too high. The driver is overheating, and its thermal protection circuit is kicking in. If this is the case, the driver can sometimes issue steps even when no motion command has been given.

Your best approach is to begin with both driver at the lowest setting. Issue a long 200mm move on the x axis, and adjust the current setting clock-wise until the carriage begins to move. This position is usually between 9 O'clock and 11 O'clock on the flat part of the dial. Stronger stepper motors may go a bit more.

Since this position is at the bottom of the range, it is best to turn the pot a little more. Just a little.
Re: Layers shift when printing circles.
August 05, 2012 01:36PM
You might want to check if the pulley isn't slipping on the stepper shaft.
If you are losing steps it often looks different than this. (more sudden and not so nicely skewed.
I had a similar problem which was caused by the pulley slipping on the axis of the stepper.
You need a little flat on the axis of the stepper for the setscrews to grip on.
Good Luck!
Re: Layers shift when printing circles.
August 08, 2012 02:39PM
Had the same problem the first time i printed something not a calibration square had to lower the DEFAULT_XYJERK and DEFAULT_MAX_ACCELERATION as the printer was acting like a demented demon. Now its just a smooth slide back and forth on the y and x axis.
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