Woooo I fixed it! Well 95%

https://imgur.com/KibBGNV

I guess the difference the carriage warp was making on the mag ball positions was enough to cause the effect. Switching over to eccentric spacers significantly improved it!

@number40fan:

I printed a 40x40x40 single walled object in vase mode. If I look hard enough, I can see the lines you are talking about. But, dang, I do have to look to see them.

Thanks for giving it a try Perhaps I've hit a limit of some kind. I wonder if it's delta specific

E3D is sending me a new pinion gear, but some more interesting developments..

Someone with a well tuned D300VS printed the same objects I'm having this effect on (single perimeter, PLA) and they're also seeing the patterns, but observed it doesn't seem to impact the actual surface, just the way light is interacting with the print. They were using the stock extruder.

I also observed when printing a hexagon shape, the sides closest to the towers had the lines more prominent, and the sides on the opposite were hardly visible. Seen here https://goo.gl/photos/hnc4CBySY3rispkYA If I print next to a tower I can see it on all sides.

I'm not sure what carriages they were using but I know the stock ones use a screw to tighten the carriages to the rails, and doing so creates a .5mm to 1mm difference in magball spacing between the carriage balls and effector's. I have some eccentric spacers I may reprint carriages for…or I might just let it go at this point : )

I think you're right about the extruder - here's a clip of the titan idler that rides tightly against the stepper gear.

https://goo.gl/photos/Yc6R1PegXFZpS4Nb7

I suspect this wobble shouldn't be here, though it takes a full rotation which is much longer than the space between the diagonal line steps..so I'm not sure. I think tightening the idler impacts the lines a little bit so that's more evidence.

@MiR:

Are your pulleys running smoothly? I bought one pulley that had a non-centric bore, as the pattern on the parts is regular that's perhaps worth checking.

Aaaaaahhhhhhhhh I THINK YOU WERE RIGHT. One of my pulley's isn't concentric. Gotta order a replacement. Wow thank you so much for suggesting that - I never would have found it. I'll mark this answered if it proves to be the problem.

Ran some more tests where I changed the steps per mm to see if the diagonal lines changed angle and turns out they dont - it's just hard to tell sometimes but the angle of the lines is different on some sides of every cube.

Now I'm much more suspect of the pulleys as MiR suggested - will check that next.

I took apart the titan extruder and noticed the idler that rides against the hobb gear has a bit of wobble to it - and I think it's from the gear?

https://goo.gl/photos/hzUhnTGuvzgFeM6t9

Flipped the gear and still see it
https://goo.gl/photos/oziQfsHv4FPEwABk6

Tried with just a piece of plastic to remove the idler as the problem and moved the gear up to try to eliminate any affect from the shaft.
https://goo.gl/photos/hkQEasigaQgCNcNu7

Also tried tightening the grub on the round part of the shaft instead of the flat in case it would take up the play better but didn't notice a difference.

It needs a full rotation to achieve the wobble, and with the lines as tight as they are I suspect that's not the problem.

To summarize - factor's that don't seem to affect it
-Print speed
-Hotend Temp
-Heated bed on or off
-Fan speed from 50% - 100%
-Part position on bed
-Part rotation
-Extruder stepper current changes
-Lowering extrusion factor in web interface to 85%
-Increasing stepper wire gauge
-Twisting stepper wires / thermistor wires
-Extruder stepper interpolation turned off
-Extruder tension
-Filament slack
-Swapping extruder stepper for a different type (started with .9* and then tried a 1.8*)
-Two different e3d hotends / extruder configurations (Titan and D300vs stock)
-Layer height (tried .15, .2, .268 - all look the same)
-Changing the extruder steps per mm

@T3P3Tony:

See what difference not interpolating the extruder steps makes:

M350 E16 I0

Thanks for the idea - I tried it but surprisingly it still looks the same.

I also tried moving the extruder stepper wires, hot end power and thermistor wires over to the second set of plugs - didn't help : /

Pretty sure the shaft on the stepper wasn't bent - pattern is too tight for that to be the problem anyway.

I tried swapping in a different stepper on the extruder and still get the diagonal lines - same angle too (which might make sense since I halved the steps.

17HS08-1004S
Motor Type: Bipolar Stepper
Step Angle: 1.8 deg
Holding Torque: 13Ncm(18.4oz.in)
Rated Current/phase: 1.0A
Voltage: 3.5V
Phase Resistance: 3.5ohms
Inductance: 4.5mH ± 20%(1KHz)

Set to 850 ma and 410 mm/s

@MiR:

Are your pulleys running smoothly? I bought one pulley that had a non-centric bore, as the pattern on the parts is regular that's perhaps worth checking.

Great idea, though now that Ive had a change in the pattern based on small adjustment of the extruder stepper steps, I dont think this would be it.

Tried a few things with simplifying, rerouting the wires for the extruder stepper but didn't have any luck.

Extruder stepper ratings :

Rated current: 1.4 A/phase
Rated voltage: 2.7 v
Inductance: 2.0 mH/phase

I had this set to 1200ma (85% of the 1.4A rated should be about right?)

Dropped it to 1000ma, then 850 - didn't help.

I wonder if my stepper shaft could be bent…