I have a slice thermistor too and my educated guess is that it's not reliable at (very) low temps. It makes sense being a thermistor for high temps. I added H6 option to add 6 degrees in the low end, but it's purely cosmetic.
I checked with a thermal camera and I'd say as soon as you reach 100C the reading is accurate.
@Phaedrux before the auto-tuning I tried a second time manually to see if values changed. In doing so I believe I've found the problem.
The new values are M307 H1 R2.9 C204.0:102.0 D4.00 S1.00 V24 that are very close to the previous ones and indeed I got a fault again BUT it works perfectly if I remove the second C value.
So it seems that at least the toolboard has some issues with the second cooling time constant, removing it solves the issue (or at least it doesn't trigger the issue).
Remains that the duet should not fault without error.
So I got this texture on a corexy I've built. It's 3x leadscrews+rails.
The pattern looked very regular, so I thought z wobble.
Changed z motor mounts, leadscrews, couplers aaaand... same result. Nothing changed at ALL.
Pulled the trigger and bought a digital microscope.
I printed a 1-wall cube. This is the result of two opposite sides (sections).
What the hell is going on? The wobble in just on one side of the wall?! Help me Duet3d Forum, you are my only hope!
Extruder is bondtech. Extruder motor I tried with a 1.8 moons and a 0.9 LDO. Nozzle is brand new high quality. If I change layer height the "wobble" seems to be the same (that's why I thought it was caused by the z axis).
I have 2 part fans connected together and 1 thermally controlled tool fan, they are all 12v connected to the duex5. I'm in a corexy setup and thinking of reducing the number of wires that go from the head to the duetwifi/duex5.
It is my understanding that the positive lead is shared with all fans. My idea was to use just 1 pos and 2 negs. On the duet side I'm connecting the 2 part fans together to one header (+ and -) and the tool fan to another header (just the negative since the positive is shared on the other header). Does it make sense? Does that impact on the total max amperage? Just wanted to check this config with you before burning my duet 
Thanks!
PS: I wanted to add that both this forum and the wiki are an incredible source of knowledge, I was able to go from zero to full functioning corexy by just RTFM so thanks guys!
okay I was ready to swap the wifi module but before that I tried to just "extend" the antenna... believe it or not it worked. I hadn't a single disconnect since
Basically cut the onboard antenna and soldered a new one. The antenna must be of a very specific length (check 2.4 antenna length) but apart from that it's a 5 minutes hack.
Now, I don't suggest to anyone doing that... but it worked for me.
@arhi said in I thought it was z wobble...:
I can't see from the images, is the issue parallel to the XY plane or is it under angle)
they look pretty much parallel.
@mrehorstdmd said in I thought it was z wobble...:
So the line width is varying but only to one side...
Is the hot-end perpendicular to the bed?
yes but the width variation is not always on the same side. if the head wasn't leveled shouldn't the wavy lines be always on the same side?
but I'll double check that. Thanks!
How tightly screwed down is the drive gear adjustment screw on the extruder?
I tried to make it very loose and very tight but I can't say I noticed much difference.
Are the drive gears clean?
Brand new.
How consistent is the diameter of the filament you're using?
I'll double check that but it is supposed to be good quality.
Are you using any pressure advance or nonlinear extrusion?
No, I disabled everything while testing.
PS: just wanted to thank you @mrehorstdmd for your great blog, I've built my printer mostly thank to your posts
just power the rpi separately, if the duet3 is already powered via 12-36v you don't need to send the 5v back from the rpi to the duet.
I haven't looked into it, but I'd think you need a common ground for the main vin and the rpi 5v. I bet either the forum or the wiki have the answer to that.
this is very interesting, following this thread.
I'll have a look at your code soon and possibly compile it on Linux.
Keep up with the good work
your build is really something. I'm particularly impressed by the tidiness and wires routing
@mrehorstdmd said in I thought it was z wobble...:
@matt3o Thanks!
Is there any play in the extruder carriage bearing block or in the mounting of the X axis rail?
Are pulley and motor mounts solid?
the extruder is mounted on hiwin rail+carriage and I'd say it's pretty solid. The pulleys are mounted on shoulder bolts secured on top and bottom.
The only thing I'm not sure about is the belt tension. It feels very tight on the short side (on the X connecting to the head) and slightly floppy on the long side (on the Y). It's a 400x400 printer. But I don't see any vertical banding... so I guess it's okay
interesting, did they develop a slicer too?
@printthatthing no problem, the forum is really a gold mine of tricks and workarounds (often better and more up-to-date than the wiki). Unfortunately I find the search not very good.
What I do is searching the forum via google like so:
happy printing!
you can find multiple references to that warning on the forum. Here's one
https://forum.duet3d.com/topic/7971/warning-heater-appears-to-be-over-powered?_=1611391114818
@deckingman I see a lot of people using 128 microsteps (with interpolation) on XY in corexy. I don't know if it's because some extensive testing or it's just psychological
I guess it's all down to how good the driver is at interpolating...
ohmy I thought I was going insane until I saw this post.
I thought it was a problem with my extruder motor or the extruder itself... or the filament tensioner... I went ahead and recabled everything and twisted the CAN data wires, added ferrite bead... thanks god I saw this post before I rebuilt my printer all over again 
This is just to say that I'm experiencing the same issue with a toolboard.
@engikeneer I actually tried that and strangely enough it doesn't work... that is very weird as it doesn't resonate in diagonals so the problem seems to be in the interaction between the motors.
PS: also belt tension doesn't seem to effect much if at all
okay more testing today. I played with stealthchop and spreadcycle but really nothing has the slightest effect on this issue. Also acceleration and Jerk don't play any role in it. Really the only thing that works is setting the amperage to half what it is needed.
I also tried with a different set of motors and resonance changed and it's to reasonable levels... but I can't use them in "production" because they are way underpowered for my build.
So I guess the only way is to buy new motors and hope they will work.
I have a rather big corexy (40x40cm), wondering if using a 9mm belt would change anything... or maybe nema23.
gosh this hobby is frustrating.
so, I tried with bigger/sturdier XY motors brackets and also with some dampening material but nothing seems to solve this issue. I made more tests and the problem starts at approx 3800mm/m up to about 4600.
If only one motor moves (any of them) the problem doesn't come up. If both moves especially in straight lines it's really bad (I can feel the whole printer vibrating)
Nothing that I tried seems to have any effect except reducing amperage. I have 2amps motors that I run at 1.4. Running them at 1amp reduces drastically the resonance.
Any suggestion?
@Phaedrux before the auto-tuning I tried a second time manually to see if values changed. In doing so I believe I've found the problem.
The new values are M307 H1 R2.9 C204.0:102.0 D4.00 S1.00 V24 that are very close to the previous ones and indeed I got a fault again BUT it works perfectly if I remove the second C value.
So it seems that at least the toolboard has some issues with the second cooling time constant, removing it solves the issue (or at least it doesn't trigger the issue).
Remains that the duet should not fault without error.
I have a very similar issue.
At around 50mm/s the printer starts resonating. It doesn't do that at any other speed. I was about to post a message about that, but I'll post my findings later today here instead.
In the meantime you may try to change the microstepping.