My printer just started printing circles as ovals and squares as rectangles...

So my DIY Prusa i3 has been printing perfectly, using Simplify3D to slice the STL's. But all of a sudden circular parts are coming out as ovals and squares as rectangles. the quality is still perfect... but the circles are not longer circles.
I've made no changes to the firmware.

Printer: DIY Prusa i3 Slicer: Simplify3D Firmware: Marlin

I kept having big problems so I uploaded a copy of the firmware I have run successfully for months.

Today I've printed a test cube 20mm x 20mm x 20mm

The cube came out as Y=21.5 X= 16.15 Z=20.5. so as you can see it didn't go wel... however it is worth noting that the quality of the print is fine, good even, but just all the wrong dimensions.

The steps per/mm are as follows: #define DEFAULT_AXIS_STEPS_PER_UNIT {80.5,80.5,405.6,456}

So the X and Y values are the same but getting very different dimensions when printing...
Any ideas, stepper driver or stepper motor perhaps?

Check that your pulleys on the motor have the set screws tight and they are not slipping.

Thanks for your reply, I'll double check those tonight. I've watched the connections during prints and they don't appear to slip and the quality is still so good that I don't see how it could be slipping and maintain the quality. But I will definitely check thanks.

Try using a different slicer. If they still come out as rectangles then you know that simplify3D is not the issue and can focus on hardware / firmware

Have you made any changes no matter how small you may think between the correct dimensions and now

I'll try with a different slicer and confirm.

Well I've been racking my brains about that as I cannot recall making any changes what so ever! The printer was running brilliantly and now its not! Very frustrating.

I intend to strip the XY axis's down tomorrow (if I have time after work...) and then reassemble and test....

The most confusing thing is that the steps per/mm for X/Y are exactly the same... yet the result of the two axis are so different....

Has any one ever heard of these symptoms with regards to hardware failure?

I don't see any point in stripping the axis just yet.

Having a smaller dimension is usually a sign of skipped steps. A slipping pulley can be hard to spot, draw a thin line from the centre of the motor shaft and up onto the pulley, run the print and see if the line still matches up. Also look at belt tension and try increasing the stepper current to that motor.

Skipped steps would usually show signs of overextrusion or misaligned layers.

Do you have an old gcode file that you could print again?

Edited 1 time(s). Last edit at 05/02/2017 02:17AM by o_lampe.

Just to let everyone know, I sorted it I think it was a belt or pulley issue on the x asix. I re-assembled it and re-tentioned the belts and all seems well again. Thanks for the help