Update: Shrink-tubing around the bearing worked for a short while, but since the tubing is soft it quickly developed a groove and began to slip again.

Still much better than using the bare shiny metal, but I did wind up getting a negative movement on a section of complex infill. Since negative values for R do not seem to work, even setting minimum to 0 I will still get pausing without actual jams/issues on a job.

Next attempt will be to use salt water and electricity to etch the outer rim of the bearing. I have done this with other SS items and the result is usually an even, "frosted" surface. I don't know if this will be enough "texture" to grab the filament or not.

@steveyyc Update: Salt Water Etching didn't touch the stainless so I resorted to an emery board and the garnet abrasive took the shine of the bearing very quickly.

It's definitely going to be hard to get negative values now - the range has shifted to min 555% and max 588%

Provided this result lasts through a few more jobs I think sanding the bearing may be the solution to the slippage.

I have a "purge.g" in my macros subdirectory.

I call it with an M98 command.

M98 P"/macros/printing/purge.g";

; purge.g
; macro to purge leave a print in process and purge some filament in a safe location before returning to the print
; currently configured for use with a fixed (x,y,z) purge bucket
; NOTE: When using G1"R" to restore a position, axis args are offset and any axis not mentioned will not restore
; (So use X0 Y0 Z0 with restore moves or else the tool will just sit there)

G60 S2 		; Store Current Tool Coordinates in slot 2 (same as would occur at tool change)
G1 X0 Y0 Z5 R2 F6000	; move up 5 mm @ 100mm/s

G1 X0 Y80 F12000	; move to a spot above the bucket location (in front of Z tower) @ 200mm/s
G60 S1			; store position slot 1
G1 X0 Y80 Z0.1 F6000	; move to purge coordinates @ 100mm/s
G1 E20 F900		; purge 20mm filament @ 15mm/s
G4 S2			; Wait for 2 second &
G10			; retract to minimize ooze
G1 X0 Y0 Z0 R1 F6000	; return to stored position 0 (above purge) @ 100mm/s
G1 X0 Y0 Z5 R2 F12000	; return to stored position 2 (Z offset 5mm above print) @ 200mm/s
G1 X0 Y0 Z0 R2 F3000	; return to stored position 2 (contact print) @ 50mm/s
G11			; unretract

; print will resume at this point

@cosmowave I have a stock 220mm build plate with a 200mm ultrabase plate on it. The bed is a little loose at room temperature with a fraction of a mm play in X/Y but when it's hotter than 50 degrees it does not move in x/y. If I want it to be rigid at room temperature I can loosen the M3 nearest the towers and rotate the mounts inward a bit and take the slack out of the system (That's why I have the adjustment slots in the mounts).

I have considered adding some springs under the bed to pull the three mounts inward at any temperature which would get rid of the tiny bit of slop when the bed is cold but I rarely print on a cold bed so I haven't gotten around to it.

@brunofporto I was considering something like this stuff from Rustoleum

https://www.rustoleum.ca/product-catalog/consumer-brands/epoxyshield/concrete-accessories-and-additives/anti-slip/

If you don't want to use conditional processing (or upgrade to RRF3):

You could set your firmware retract for the tool in the tool change macro (ie tpostn.g for tool n):

M207 S-10  F3600 ; retract 10 mm

then use G10/G11 firmware retracts in the pause command

G10 ; retract the filament by a tool-specific amount

Wouldn't you effectively get separate jerk settings for printing and moving if you set the jerk for E to the print jerk and X,Y,Z to the move jerk?

The firmware would be smart enough to never jerk the move axes faster than the extruder can keep up, so during printing wouldn't this effectively limit the jerk on the move axes to the E axis value?

@spllg

1. If you put an M80 command in your config.g does the ATX control show up? On my machine it will only appear in the interface after the power supply has been turned on once by manually entering M80.

2. Do you have a move command at the end of your print to move to a fixed position that coincides with layer 249? If you put a comment starting with the letter "E" after that move like this:

G1 Z50   ;E

The Duet will not add that Z value to the height of the object and you should see the height of the last printing layer instead.

Got mine printed and assembled, but I'm getting an extremely large range of values for min & maximum. Does this mean my bearings are slipping?

M591 D0
produces the following:

Duet3D laser filament monitor on input 4, disabled, allow 25% to 440%, check every 3.0mm, current pos 5.7, brightness 110, shutter 35, measured min 4% avg 181% max 492% over 994.7mm

@Ntrack
When you initate a tool change the Duet stores the current tool coordinates as if you'd issued the following G60 command:

G60 S2

You can also store coordinates in S0 and S1

Using this stored location (S2) you can move up 15 mm by issuing a G1 command with the "Restore" argument R

G1 R2 Z15

This will move to the location stored in slot 2, with an offset of 15 in the Z axis.

I find this much easier to reverse than switching to and from relative coordinates. For example, you can perform whatever purge maneuvers you need to do and then just issue the command:

G1 R2 X0 Y0 Z15

to return to 15mm above the last printed point on your model.

G1 R2 X0 Y0 Z0

will put the tool back in contact with the model and should probably be the last instruction in tpost.g

@techni You have stated that you don't want to use a prime tower, but would you consider an ooze shield?

Depending on your slicer you can either generate an ooze shield or extend your skirt upward to keep it the same height as your object. If all your filament changes happen outside that perimeter the ooze will usually get scraped off by the ooze shield instead of sticking to your print.

Depending on your model geometry an ooze shield can represent a lot less plastic waste than a purge tower.

The IceSL slicer has a specific option to generate a close-contoured ooze shield which wastes as little plastic as possible while still being easily removed after the print finishes.

@nxt-1
I think this flex/bed-sagging might be compensated is some part by the leverage of the system.

The piezo sensors furthest from the probe point are being flexed by the bed as well as the piezoelectric sensor closest to the probe point but the deflection at those point is larger because the probe point is acting as the input of a third class lever with the closest piezo sensor acting as the fulcrum and the further-away sensors are the load.

I suspect the maximum deflection at any point before a signal is detected would need to be a higher frequency harmonic of your sketch with a proportionally smaller deflection amplitude at each anti-node. Since I feel like this is getting into Laplace Transform territory I have to admit my math skills aren't up to quantifying this.

I expect there are a few "worst" places to probe (the midpoint between two sensors for example) which produce low-magnitude signals at two sensors and do not have any moment producing a signal at the remaining sensor.

Anywhere inside the triangle enclosed by the three sensors should produce a signal at all three sensors. Any point outside the line connecting two sensors would produce a signal at the third sensor with negative magnitude (because now its a first-class lever) and that might cause some odd behaviour depending on how the signals are processed in the probe's firmware but so far my installation hasn't had problems interpreting probe results at those locations.

If a very large round bed experiences this sort of measurement inaccuracy then I would suggest the bed is under-supported or under-built anyway and the bed dishing could/should be dealt with by some combination of stiffening and a better multi-point support system similar to that used for telescope mirrors.

@cosmowave I have a stock 220mm build plate with a 200mm ultrabase plate on it. The bed is a little loose at room temperature with a fraction of a mm play in X/Y but when it's hotter than 50 degrees it does not move in x/y. If I want it to be rigid at room temperature I can loosen the M3 nearest the towers and rotate the mounts inward a bit and take the slack out of the system (That's why I have the adjustment slots in the mounts).

I have considered adding some springs under the bed to pull the three mounts inward at any temperature which would get rid of the tiny bit of slop when the bed is cold but I rarely print on a cold bed so I haven't gotten around to it.

This is one of the three mounts I built to hold my piezo sensors under my delta's print-bed. The bed just has a large knurled nut on the m3 bolt to make each mount point adjustable in Z. The bolts are long enough I can adjust the bed up and down through 5mm which is plenty for tramming.

It's only held down on the piezo mounts by its own weight.

The last time I saw this error it was because one of the part-cooling fans was blowing on the bed and that was slowing the temperature increase.

The time before that it was because one of the heater wires wasn't tightly secured.

It's not something simple (but easily overlooked) like that, is it?

If you don't want to use conditional processing (or upgrade to RRF3):

You could set your firmware retract for the tool in the tool change macro (ie tpostn.g for tool n):

M207 S-10  F3600 ; retract 10 mm

then use G10/G11 firmware retracts in the pause command

G10 ; retract the filament by a tool-specific amount

@Rat_Patrol
Once you have probed the bed with the command

G29 S0

the result of the mesh probe is saved to /sys/heightmap.csv

Without probing the bed again, you can load the saved result from an earlier mesh probe using the command

G29 S1   ; this loads the contents of /sys/heightmap.csv

How much filament have you run through your nozzle? Did you get a hardened nozzle or have you been using a brass one? Have you used any filaments that are abrasive like carbon fiber or glow-in-the-dark? Any materials that hydrolyze? (200ºC for PLA would be too hot in my machine & would definitely make trouble unless I kept the filament moving)

When I had a (previously dialed in) material suddenly experience a drop in quality that couldn't be explained by mechanical or electrical malfunction in the past it turned out to be the nozzle - it had accumulated residue on the inside and had worn away on the outside to the point where the orifice was no longer producing a circular and consistent output stream.

What about putting pieces of high-friction tape on the mating surfaces of the magnets? HF Tape is inexpensive and removable/reversible. It comes in rolls or dots and is designed to resist this kind of shear movement.

@pipersw I did not know that M81 would also work. Thanks for that!