S3D positioning errors in gcode

[markqvist]

For some reason, S3D is generating incorrect positions in the gcode when slicing. Have a look at this picture:


(S3D slice with thick bands at the hole positions)

I've been trying to troubleshoot this for a looong time. Initially thought it was caused by some sort of mechanical error in my machine (Replicator 2X), so I calibrated, adjusted, tightened, lubed and whatever for ages and ages (even rebuild the entire extruder), to absolutely no effect. In the end I gave up and tried slicing with MakerBots software instead. Problem solved:


(MakerBot slice on left, S3D on right)

After looking at the gcode generated by Simplify3D, it's actually no wonder why the machine is producing these bands. It's right there in the gcode! The machine is just doing exactly as it's being told by S3D

I have no idea what could be causing this though.. Some sort of float rounding error? Just a regular weird bug?

It's relevant to note that this happens on ALL my prints, as soon as theres some sort of continous shell with holes in it along the perimeter at some points during the print. A topology like that will cause these kinds of bands every single time.

I'm quite dismayed. S3D is pretty near perfect in allmost all other areas, but this is just a dealbreaker, when the program itself is utterly ruining the quality of every single print

Has anyone experienced this? Or better yet have an idea for a solution?

On the upside I now have an extremely well calibrated machine

[andrewk72]

There's a very easy way to check and see if the software is actually creating positioning errors. Open the gcode file that it creates within a text editor and then check the XYZ coordinates in that file. Do you see any that look different?

The preview in S3D does the same thing. So if you don't see the misalignment in the preview them it isn't due to the gcode that the software is creating.

[markqvist]

Thanks for the input, but as i mentioned in my first post, I did already look at the gcode generated by Simplify3D, and found that to be the source of the errors.

After looking at the gcode generated by Simplify3D [...]

If you want to see it, here's two sections that are supposed to be identical, one from layer 60 and one from layer 110. This corresponds to a layer around the middle of the first hole, and a layer in the section with no holes following that. These are from the corner section, as it nicely demonstrates how the positioning is off in both axes.

Code: Select all

G1 X30.359 Y5.814 E0.0518
G1 X30.310 Y6.229 E0.0164
G1 X30.191 Y6.623 E0.0161
G1 X30.006 Y6.992 E0.0162
G1 X29.816 Y7.256 E0.0127
G1 X29.525 Y7.550 E0.0162
G1 X29.188 Y7.788 E0.0162
G1 X28.896 Y7.932 E0.0127
G1 X28.502 Y8.055 E0.0162
G1 X28.088 Y8.108 E0.0163

Code: Select all

G1 X30.360 Y5.744 E0.4501
G1 X30.312 Y6.218 E0.0096
G1 X30.225 Y6.535 E0.0129
G1 X30.053 Y6.911 E0.0162
G1 X29.819 Y7.251 E0.0161
G1 X29.579 Y7.503 E0.0136
G1 X29.268 Y7.739 E0.0153
G1 X28.903 Y7.929 E0.0161
G1 X28.511 Y8.053 E0.0161
G1 X28.098 Y8.107 E0.0163

The errors in the positioning are "small", but definitely large enough that it will show up in the print.

The preview in S3D does the same thing. So if you don't see the misalignment in the preview them it isn't due to the gcode that the software is creating.

I don't think you can make that conclusion without knowing the specific code that generates the preview and the gcode (pardon me if you are part of the dev team, I don't know). To me this seems like some sort of rounding or float precision error. The misalignment does not show up in the preview, but it does show up in the gcode and the printed part.

Furthermore, I tried correcting the gcode positions manually in a small part of the file, and it printed flawlessly.

So there you have it, there's definitely something weird going on with the positioning in the final file.

[CompoundCarl]

Keep in mind that your model was exported as an STL file that uses triangles to model those curves. The edges of those triangles will change over the Z-height (since they are triangles and not rectangles). Some CAD programs as worse than others, but it's very common to see the coordinates change by a small amount as they follow the triangle surfaces.

Also, if you actually plot the coordinates you listed below, you will see that they perfectly overlap with each other. You're plotting coordinates around and arc. They both draw the arc perfectly, but one starts at a slightly different position (again, because your model uses triangles). So I see nothing wrong with the coordinates that you posted.

In my experience, this is far more likely an issue with mechanical backlash or ringing. I've done a lot of printing with S3D and I have never seen it put coordinates in the wrong place. It follows the model, exactly as you provide it.