The top ones that pinch are the tension adjustments.
I tightened the tension bolts on all four trucks until they had no physically perceivelable wobble. They don’t seem to be tight enough to restrict movement. Same for the core.
I ran three tests - one with the V1E pen mount, one with the spring-loaded mount I designed, and one with the spring-loaded mount plus a lateral movement guide, which after wrapping the rear of the pen with just enough painters tape, has zero X/Y movement within the mount, and just a light touch of spring tension to overcome minor bumps/elevation changes.
All tests were done with the same feeler gauge as 0 and 0.5mm plunge, the same origin point without moving X/Y.
There’s still some imperfections. The V1E mount is the best of the bunch but still not really completing trapezoids and squares.
At this point I’m wondering if there’s something I’m doing wrong in Inkscape to cause the path to have problems in the first place. I’m happy to try any further troubleshooting/testing on the Primo if anything else exists to try.
Ignore the skips in the ink, that’s known to be the pen’s fault. Also ignore the curves being off, I’m just using Estlcam to move them to just right rather than keep chasing that particular dragon.
watch the pen in action very closely. that much movement you would be able to see if the pen springs around or not. the issues are relatively huge. we normally deal with much smaller issues.
the crown is proven good, any issues with that?
The crown itself does not come out evenly. I plotted it and observed the pen through the entire process. As far as I could tell, the pen didn’t skip. I think I heard the right hand Y stepper thunk at some point, sort of like the sound it makes when I try to move it past the limit, but not a long grind - just one thunk of a grind. I’m not even sure it was the Primo, it could have been something else in the house.
There is a mismatch in sizes on parts of the crown. The circles look like they’re flattened across the top a little, and the central parts are misaligned as is the bottom long part:
I can assure you that is not a skipped step. skipped steps are drastic and accumulative, they don’t fix themselves.
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At this point I am fairly certain your z wiring or gantry drag chains are causing the issue.
I took off all the X and Y drag chains and just enough Z drag chain mounts to ensure it’s pretty much zero tension on anything. I basically babied them through a plotting session. No real change.
I also took some time to redo the belts in case those were the issue. I basically got them to just a few quarter turns of the tensioner screws shy of not being able to move, and they’re darn near perfectly in sync for tension. They have the same tone when I pluck them at either near or far X or Y axis. Without borrowing my wife’s condenser mic and hooking it up to a guitar tuner, the belts are synced and seem OK - but no real change, the issues persist.
In the interest of making sure it’s not my amateurish Inkscape skills, I put together a quick SVG of a completely new blueprint. I took serious care to ensure all the paths were snapping to cusps, lines, etc. It still occurs, this time I caught it on video: https://imgur.com/Uapdk42
The issue happened at a few points before I started recording but you can see what happens from 0:45-0:36 on the countdown timer in the video; it deviates by a mm or two when it finishes the shape. Same thing from 0:36-0:25 and 0:14-0:09.
Literally the only thing left is your pen. It must have slop in it somewhere. Hot glue it in place and use the zip ties. change pens, something. Those drawing I showed that we do at the RMRRF, those can easily be drawing for 2 hours, finish, Run the file again and it will home and draw again for another 2 hours with no perceivable deviation.
The Crown test gcode is known and proven, no need to second guess anything on the Gcode chain, that file has been drawn countless times and yours is bad.
This picture right here, you have removed this section of constraint that goes tight?, all wires should have a large loop in them.
If you wanted to look for some sort of systematic errors you can try this, Test Pattern Generator
The only thing left I can thing of is rotate all 6 of your tubes 20degrees. in case you have a rough spot or something the bearings are hitting. You can move the pen to a bad spot in the drawing and check each bearing position for a bad spot on the tube.
This sucks for me as I am sure I could find it in person in less than 15 minutes.
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I agree, it looks to me like the pen is moving in the holder. The tip of the pen doesn’t always make it to the end of the path and some (many?) of the path start and/or end points are shifted. This implies that there are places where the pens forward movement encounters enough drag to shift the tip backwards a bit in the holder. Based on where that would need to happen to explain the shifted start/end points, it looks like the pen stays shifted until there is enough drag to cause another shift (relative to whatever direction the pen was moving in).
It looks like it has the same issues, lots of lines that don’t make it to/are offset from an intersection point.
I don’t know anything about pen holders, but I’d want support a lot closer to the tip, e.g. with a hole for that metal part.
…Engraving the crown with a V-bit (MDF or foam) should answer the ‘is it the machine or pen holder’ question.
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Thank you all for the feedback and suggestions thus far - I have taken them all into action with a lot of trial and error. I got as far as hot-gluing a pen to the V1E designed pen holder and running some of the test patterns, which seemed to complete without incident, until they trained the hot glued pen of its ink. 
The Kraftwerk wireframe portraits do indeed have the issues you’re mentioning, they escaped first notice since I was pretty happy with the result and it didn’t have the same immediately obvious issues as the blueprint.
I’m taking a break from the plotter question and have swapped into the router for another project. Once that’s done I’ll melt the hot glue, replace the pen, and try once more.
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