Rev e dual extruder nozzle distance issues

[saaronm]

When we first received our printer, it worked exceptionally well. We printed dozens of items. However, recently when printing any filament we have been having inconsistent results. When printing some items the nozzle is the appropriate height and adheres to the print bed. However, when printing a specific, large piece; the nozzle extrudes from a few millimeters up and drags the extruded filament around. This results in shifting layers, curves becoming straight lines, poor adhesion to adjacent strands, etc. It is especially frustrating because when I print Benchy, it printed just fine. It even measured to most specs.

So far I have tried:

Different filament
Different types of filament
Checking belt tension
Bed leveling (both in Simplify3D and the Quick start tool)
Starting height adjustment

Here is a video of it in action:
https://1drv.ms/v/s!As30tIUcYjWMrGiXA6G1jV-h1LlI
At about 42 seconds you can see it pretty well. Filament is extruded and it sticks initially but then as it tries to print a semicircle the nozzle height is such that the filament just gets pulled straight.

Here are some images
https://1drv.ms/i/s!As30tIUcYjWMrGnRYAJLx82ElX5z
https://1drv.ms/i/s!As30tIUcYjWMrGouVOO7rAx-IUlf

Any suggestions or direction would be greatly appreciated while I try to troubleshoot this!

Thanks,
Sam

[ednisley]

when printing a specific, large piece

That almost always means a non-manifold solid model with broken geometry confusing the slicer into generating bad G-Code. You can confirm that by previewing the G-Code paths at (for example):
http://gcode.ws/

Various mesh-repair tools may be able to "automatically" fix the model in various ways, but the assumptions they make about what you intended to build may result in … peculiar … results. Always compare the repaired model to the original and verify the G-Code, too.

[saaronm]

So I fixed some of the issue yesterday while waiting for the post to approve. I reduced layer height from 0.15mm to 0.1mm and I can now print round shapes again. However, there is a new problem. Expansion?

First, Ed. Thanks for the suggestion! I run all my models through MeshMixer and the Simplify3D mesh tools. However, I did export the gcode and put it through that sweet website (now bookmarked)! Unless I am missing something all looks good:
http://imgur.com/yEo8l6W

So, here is the new issue. As the model prints, it expands in the X and y directions as the Z axis increases. As you can see by the Gcode analyzer image above, the print should be rectangular. Here are some images of the print I just stopped:
http://imgur.com/a/UZno0

As can be seen from the gallery above, there is some X and Y expansion as I print in the Z direction. I am currently at a loss for the reasoning behind this. I know I shrunk the model in Simplify3D, however it was a uniform shrink. I have a new model with slightly smaller dimensions I am about to try and I will update if it changes anything.

Thanks all!

[ednisley]

Unless I am missing something all looks good

What you must do is step upward through the 2D layout (in the 2D tab), layer by layer, to verify that the thread paths make sense. The overall 3D representation (that black blur) can hide many sins, particularly in layer-to-layer spacing, so I think it's pretty much worthless.

Pay particular attention to the actual Z height corresponding to each layer (select the Layer Info pane / tab / whatever to see the details), because the sequence of those steps matters.

You can select a Layer option to see the N+1 (maybe N-1) layer in semi-transparent colors, so you can verify the overlap / overhang between the threads in successive layers.

the print should be rectangular

Again, verify the actual paths on each layer by stepping upward from the platform. If they appear neatly stacked, then there's another problem.

However, the honeycomb infill looks just about perfect, right out to the edges. If it were a printer problem, then the infill would be wrecked, too, and it's not, so I think something is (still) wrong with the outside edges of that model.

Also, does the slicer complain about a non-manifold model? Does it automatically repair any problems?

Remember, an automatic mesh repair can make bizarre changes to your model. Ideally, you should fix the model, rather than hope the automatic repairs will not only fix the problems, but fix them the way you expect.

[saaronm]

What you must do is step upward through the 2D layout (in the 2D tab), layer by layer, to verify that the thread paths make sense. The overall 3D representation (that black blur) can hide many sins, particularly in layer-to-layer spacing, so I think it's pretty much worthless.

Pay particular attention to the actual Z height corresponding to each layer (select the Layer Info pane / tab / whatever to see the details), because the sequence of those steps matters.

You can select a Layer option to see the N+1 (maybe N-1) layer in semi-transparent colors, so you can verify the overlap / overhang between the threads in successive layers.

Excellent, thanks. I will do that shortly.

However, the honeycomb infill looks just about perfect, right out to the edges. If it were a printer problem, then the infill would be wrecked, too, and it's not, so I think something is (still) wrong with the outside edges of that model.

The honeycomb actually suffers from the same issue as the rest of the print. It is hard to see with the contrast from my phone, but it is tapered out in the X and Y directions (with most distortion in the Y). The distortion attenuates gradually with proximity to the center line of the print (with respect to each axis). It's kind of a cool effect if I could figure out how to reproduce it.

Also, does the slicer complain about a non-manifold model? Does it automatically repair any problems?

Remember, an automatic mesh repair can make bizarre changes to your model. Ideally, you should fix the model, rather than hope the automatic repairs will not only fix the problems, but fix them the way you expect.

I passed the STL file through Meshmixer, Autodesk Inventor, SolidWorks, and the Simplify3D mesh analysis tools and sliced using their respective slicing tools to check the layers. No non-manifold edges, no flipped faces, no incorrect normals, nor any other errors found. Honestly, I have never had a model warn me about non-manifold edges, so I am unsure how my software would notify more or if it would auto repair it. However, I check all new models with the tools listed before. It was originally modeled in Autodesk inventor as a solid rectangle with 7 cutouts for screws and a rail system.

I remade the model from scratch and the printer is warming up to try and print the new version. While that is going on, I will look through the 2d layers as you suggested.

Thanks!