Axis Compensation

Hi All.

First time posting. I've had my Prusa i3 Rework for about 3 years now. It is running a RAMPS 1.4 board with Marlin firmware.

Over the years I have tinkered with it an tried to get it running as smooth as possible. But I have one problem with it.

I have noticed that the x axis prints on a slant. I have printed a couple of the XYZ 20mm calibration cube to confirm what axis it was. When I put them side by side with one of the x's facing forwards and the other x turned around 180 degrees, you can see that there is a slant in the x axis.

I have gone through all the calibration and tightening of belts, screws and other bits that could be tighten and I have came to the the conclusion that the x axis is slanting due to how I assemble the printer. For me to fix the slanting x axis, I would have to drill new holes in the aluminium frame but that wouldn't work as the holes would overlap the existing holes.

So my question is, beside running RepRapFirmware and using the M556 compensation command, is there a way to slice the object I am printing or some other command that I can use to compensate for the slight slant on my prints?

No, there isn't a way that you can compensate for that. You need to slacken all the fastenings that hold the frame together, and set the frame up so that the X axis is square to the Y axis. The best way to check that is to measure the two opposite diagonals, which should be of equal length. Then tighten everything up without moving it.

Edited 1 time(s). Last edit at 02/19/2017 12:32AM by Supermec.

A slant in the x tells me that ether one of your z motors have missed steps, or that your bed is at an angle. Both are an easy fix.

Go and grab a string level (should be a few $$$ from a hardware store) and place it on your x axis, then rotate the low screw by hand till the bubble is in the middle.

Then level your bed to the the adjusted x axis. If you are using 4 point bed leveling (a screw on each corner of the bed) maybe look to changing to a 3 point system, as well 3 points define a plane, 4 points will most likely give you a bow in the plate

Quote
Supermec
No, there isn't a way that you can compensate for that. You need to slacken all the fastenings that hold the frame together, and set the frame up so that the X axis is square to the Y axis. The best way to check that is to measure the two opposite diagonals, which should be of equal length. Then tighten everything up without moving it.

Thanks for the response. I did look around on GitHub yesterday to see if there was anything happening in this space for the X/Z axis skew.

When I get a chance, I will loosen and wiggle around the z axis rods to see if I can square them up with the x carriage.

Quote
scottybfg
A slant in the x tells me that ether one of your z motors have missed steps, or that your bed is at an angle. Both are an easy fix.

Go and grab a string level (should be a few $$$ from a hardware store) and place it on your x axis, then rotate the low screw by hand till the bubble is in the middle.

Then level your bed to the the adjusted x axis. If you are using 4 point bed leveling (a screw on each corner of the bed) maybe look to changing to a 3 point system, as well 3 points define a plane, 4 points will most likely give you a bow in the plate

I do have the standard 4 point bed mounts, and I have used a level to get the bed and the x carriage parallel as possible. I have no problem with prints sticking to the bed, there may be a few hundred micron difference between opposite corners, but cant see how that would cause a slant.


I will try print something tall and take a picture with a protractor to illustrate the situation.

So I disassembled the X/Z axis last night to see if I could move anything around. Measured the opposite diagonals and yes, they are out by a few mills compared to each other. Assembled everything again an did a calibration test cube and measured the angle of the X axis and its out about 1.5 degrees (~91.5°).

The printed frame parts were printed by someone else, so I might print them off again and see if I can correct it. May have to pull out the drill or file to move the hole in the parts.

Another idea would be to skew my models in SketchUp by 1.5° and see if I can get them to print straight.

I thought I saw someone talk about a python script that ran through the gcode and applied some axis compensation. I'll see if I can track that down.

If anyone is/was interested, I reprinted the Z axis supports and voila! Straight...er prints.

But if anyone else is having issues with non right angle frames, follow Supermec advise.