Just in case anybody wants to do this in the future, I've solved it. The issue with having it not move when using G1 Z-999 H1 was my M574 needed to be set as a probe (Z) and I used the Z probe input pins. I had previously been trying the Z probe pins with S1 and the Z endstop pins with S1 (unsure as to why the endstop pins with S1 didn't work.)

At some point I'll show the new probing method...

Due to the shape of my printer/toolhead, there are specific points on the bed that the probe cannot reach. However, later on down the axis it is able to reach them, so am I able to exclude points from a mesh level?

e.g. I want to mesh level from X0:200, Y0:200 s20 but exclude (0,0) and (200,0)?!

When I leave my printer idle for more than 30 minutes, it starts making a 15,500 Hz sound that's quite prominent and goes away with any load (eg heater on). Interested as to what causes this, I assume it's some sort of standby state from either the duet or the power supply itself?

Just curious if there's anything I can do to stop it. My (or my dog's!) ears don't appreciate it

@dc42 I'll definitely move to AC bed in the future for sure. For now I've put two layers of cork on the underside of the bed which has now increased my max bed temp up to 105C. Can heartily recommend this to anybody also struggling with this issue.

@dc42 Cheers for getting back to me! I'm getting 23.9 V at the bed, so close enough. Good to know that's roughly in line with what you'd expect to see. I've just got some ASA which wants more like 110, so could be time to move to a 220 V bed instead.

I've got a Duet 2 wifi for hardware.

I've got a 220 x 220 mm PCB heated bed with an aluminium plate on the top (Link) which tops out at 87 degrees.

I get 4.8 ohms measuring across the ends of the wires running to the bed (when they're disconnected from the duet), and when it's plugged in I get 24.2 V across the contacts, which should be 120 W of heating. As a check I've tried measuring the current across the contacts when heating at full power and I only get 0.4 A which doesn't seem right to me.

I've run pwm tuning and the results are here

M307 H0
Heater 0 model: gain 77.1, time constant 411.2, dead time 3.0, max PWM 1.00, calibration voltage 23.0, mode PID, inverted no, frequency default
Computed PID parameters for setpoint change: P317.3, I9.035, D666.4
Computed PID parameters for load change: P31

Any thoughts as to why I'm not getting the expected heating performance?

Are you saying there is more than 1 endstop switch for z?

So after some experimentation, I've found that I don't get issues when extruder jerk is at 120mm/min and accel is at 3500 mm/min. This however slows down a print a fair bit (calibration cube took 19min20 instead of 15:42).

I've tried lowering microsteps to x8 and x4 but it just makes such a lot of noise that I don't think I want to have it like that even if it works!

@CCS86 doesn't a jerk setting that low really slow down your print? I see lots of other people using 3000 jerk on the same extruder is the thing too.

@deckingman I've just done a run of a print where it's been doing the blobbing, and didn't get any hiccups recorded

Just a shot in the dark really, what setting do you have the thumbscrew on for your BMGs with PLA? The instructions said to tighten all the way and undo 1.5 turns, but that seems far too tight?

@deckingman It's a clone, but the extruder works fine by hand and I've checked the grub screws are good.

I found my pressure advance value by doing this ringing print https://www.thingiverse.com/thing:4169896 and found that somewhere between 0.3 and 0.4 was my good value. You can see that the ringing is reduced on the Xs, but at 0.4 and 0.5 the corners start to go inconsistent.

So you're suggesting that setting extruder jerk low is just mitigating the problem and isn't actually solving it, as extruder jerk shouldn't be the limiting factor?

At extruder jerk of 300 I still can't get it to be consistent, it's only at 100 that I get better results, but that is extremely slow.

@bberger said in Pressure advance causing underextrusion/motor madness:

50mm wall. What happened was: it ended up extruding and retracting so much that it basically tried to extrude 25mm and then directly rectracted the same 25mm so on and so forth. In the end nothing came out of the nozzle anymore and all that was happening was constant extruding/retracting.

This is similar to the issue I'm ending up with. At a point where it is underextruding, it's as if it's ended up doing more retractions than it has unretractions, as the filament is no longer at the end of the nozzle. It then feels like it "catches up" and produces a blob. I have had issues with this in the past even with PA off, but I thought I'd fixed that. PA seems to make it far worse.
At the point where it produces a big blob, I can hear the "pop" sound you get when the filament first comes out of the nozzle.

I'll try using a Titan extruder instead and see if that makes any difference.

(I'm also running with DAA off)

@deckingman The thing is, here's exactly the same tower printed just afterwards with PA off, and it's fine (minus the stringing!)