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Prints skewing to Y max

Posted by friarfish 
Prints skewing to Y max
January 25, 2016 01:58AM
hi folks,
I have a problem when printing. Prints will at random heights be skewed towards the
ymax before resuming "normal" printing. The attached photo shows four attempts in
a row with only the left hand one working. This is a fairly extreme example but it is
happening about 50% of the time.

The model was sliced in both Cura and Slic3r. All were printed from a SD card in the
GLCD of my ramps/mega combo, running Marlin 1.0.2. Oh and the problem occurs
when printing from Pronterface and Cura. I've inspected the slice files of 3 prints and
no deviation/skewing is visible in any of them.

Slicing settings were
outer peri 20mm/s
inner peri 50mm/s
infill 70mm/s
support 20mm/s

The printer is a i3 prusa with sprocketed wheels on the x axis and a smooth on the y axis.
All the belts are tightened to point of not easily flexing. The printer has an inductive sensor for z
and a 4mm Al bed. I have zero issues with bed adhesion.

I'm inclined to think this is a firmware issue as it is occurring across multiple hosts/slicers but
I know I'm out of my depth with this issue.

Many thanks,

Edited 2 time(s). Last edit at 01/25/2016 02:01AM by friarfish.
open | download - IMAG0118[1].jpg (122.4 KB)
Re: Prints skewing to Y max
January 25, 2016 05:46AM
Are you sure that the hot end is not randomly flexing Y-direction? Or loose Z-direction? Or are the extruder parts straight? I haven't got problems with Marlin, well I don't have an inductive sensor.

Prusa i3, Ramps 1.4. Catnozzle 0.4mm
SketchUp - Enveloping Globoid Worm Gear - Part One - 3D Printed: [youtu.be]
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Nicer Screw Thread In SketchUp ( Bolts,Nuts): [youtu.be]
How To Model A Heart Shape In SketchUp: [youtu.be]
How To Draw 3D Printable Snap Fit Ball Joint In SketchUp: [youtu.be]
Re: Prints skewing to Y max
January 25, 2016 06:44PM
Looks like skipping steps to me.

You need to bump up the stepper motor current slightly for you Y axis, I assume you haven't tuned this yet?

Plenty of tutorials online to show you how to do this.

Alternatively you can lower your acceleration settings, but this is just masking the problem.
Re: Prints skewing to Y max
January 26, 2016 06:10AM
I checked the wobble in carriage after printing honeycomb the first time. That
was scary. The wobble seems to be limited to that introduced by the linear bearings
in the x carriage and the z axis.

If i inspect the visible layers in the z, they appear consistent with no areas of poor
adhesion. Well except when they are all poorly adhered!

Inductive sensors are sooo worth getting!

The steppers from memory are only running around 50% amps. At 1.2 i think.
Haven't played with them for months. I'm running drv8825s so i could give them
an extra 0.5a easily.

This seems more like the opposite of missed steps. It is more like randomly during
a layer change, a small pos+ Y relative offset is introduced and keeps getting applied
for a random number of layers..

I'll try the suggestions and hope come.
Re: Prints skewing to Y max
January 26, 2016 05:52PM
Try lowering your acceleration. It still looks like skipped steps in the Y plane to me, that creates a random offset that you are getting.
Re: Prints skewing to Y max
January 26, 2016 06:04PM
Also check that the pulley isn't slipping on the motor shaft.
Re: Prints skewing to Y max SOLVED(maybe)
February 11, 2016 12:32AM
Hi Nebbian,
slowed the Y acc down and the prob has seemed to have gone away.
Appreciate the pointers.

Re: Prints skewing to Y max SOLVED
February 26, 2016 06:46AM
Just closing off
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