Duet 3 Scanning Z probe

dc42

@Herve_Smith I think it's a case of damned if we release early, and equally damned if we wait until we've spent a lot more time characterising the behaviour when the probe used as the sole Z reference.

We've spent a lot of time testing the scanning function, to the point where we know it works well. So we've released a product that is definitely useful to many owners of existing machines that already have a good way of establishing Z=0, and probably capable of being the sole Z probe in some (but perhaps not all) machines with metallic bed plates.

We know that inductive sensors are temperature-sensitive, and we know that in some cases at least it is practical to compensate for the change in behaviour with temperature. So we've included a thermistor right on the coil so that we can compensate for changes in coil temperature. This might not even be necessary - it may be that the change in bed resistance with temperature is the primary cause of temperature sensitivity, in which case compensating for bed temperature will be more appropriate. Or it could be that in some machines we will need to compensate for both bed and coil temperature. Currently RRF can only compensate a Z probe for one temperature, but we can extend that if necessary.

This is a case where community input is so important, because the community has a much wider range of machines than we do. If we were to state that on a particular machine with a particular make of bed plate it is possible to use the scanning probe as the only Z reference, how useful would that really be, given that we can't guarantee that users with other machines and different bed plates will have equally good results?

Machines vary enormously, and on some of them (e.g. machines with a heated chamber), it may be that sufficiently accurate temperature compensation will never be possible. In these cases, if mesh bed compensation is required then it it still useful to have a fast scanning probe even if a separate contact-based Z=0 reference must be provided.

fcwilt

@dc42

Thanks for the comprehensive reply.

Thoughts:

could you design a 1LC board with the scanning Z probe? I would be far more inclined to re-design my tool mounts to use a 1LC board like that.
you guys are smart - really smart - design a very small "contact Z probe" and sell the whole package 1LC with scanning probe and contact probe. I would definitely go for that.

Frederick

droftarts

@fcwilt The new Roto toolboard already has a scanning Z probe on it, and is a bit smaller than a 1LC (more details to come). You may also prefer the connectors on it!

Ian

fcwilt

@droftarts

Is this an E3D product?

If so, what is the timeline?

Thanks much.

Frederick

droftarts

@fcwilt We designed it for E3D, and it fits on their new Revo Roto extruder https://e3d-online.com/pages/revo-roto-landing-page, which is tiny. But it is available separately too. https://www.duet3d.com/Duet3RotoToolboard
Revo nozzle, coil for scanning Z probe next to it, and standard connectors for E3D components around the edge of the board. For mounting, it mirrors the two screws that hold the board on the other side of the extruder.

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Ian

fcwilt

@droftarts

Thanks much.

I have signed up to get emails.com

Frederick

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deckingman

@dc42 @droftarts @T3P3Tony. On the basis that you would like feedback from the wider community, and a range of different machines, if you want to loan me one, I'd be happy to graft it onto my machine and run some tests. It's currently fitted with a Bondtech LGX Ace / Slice engineering Mosquito and I use the nozzle itself as a Z endstop via a hinged mount and two brass plates that form a switch. That arrangement is extremely repeatable and AFAIK, not at all temperature sensitive so would be a good comparison to see if your scanning probe can be used as a Z probe. I can also print edge to edge (400mm X 400mm) without mesh compensation so having a height map might shut down the naysayers who keep telling me that isn't possible (despite multiple videos showing otherwise). Anyway, the offer is on the table.....

dc42

@deckingman thanks, we would certainly value your input. Do you print direct on a metallic bed? You will need to install the latest 3.5.0-rc1+ firmware; is that OK?

deckingman

@dc42 said in Duet 3 Scanning Z probe:

@deckingman thanks, we would certainly value your input. Do you print direct on a metallic bed? You will need to install the latest 3.5.0-rc1+ firmware; is that OK?

Ref the build plate - not at the moment but that will change. I'm currently printing on 6mm thick glass but intend to try some sort of PEI sheet. Glass has worked well for me but I tire of using 3DLac and times move on. As I understand it, your probe will measure the topmost surface of a metallic sheet, so anything on top of that must follow any contours of the underlying metal sheet for the readings to be valid. By "metallic", do you mean ferrous metal or will it work with aluminium? I'm thinking along the lines of sticking PEI directly onto the aluminium plate but no purchase decision has yet been made so I could use steel backed PEI or some such.

Ref the firmware, I don't mind trying a release candidate as long as I can revert back to the stable version. I envisage making a new aluminium rear carriage plate which will accommodate the new tool board and probe as a well as a part cooling solution that I'm working on. So by the time I've done all that, the firmware might be stable in any case.

dc42

@deckingman the tests we have done have been on flexible magnetic steel plates, but aluminium should work too. As you run your machine in standalone mode you can revert easily to firmware 3.4.6 but of course you will lose the scanning probe functionality (which I know you don't actually need anyway). It would probably be OK to leave DWC at version 3.5.x.

Let us know when you have made a decision on the bed surface.

jens55

@deckingman said in Duet 3 Scanning Z probe:
As I understand it, your probe will measure the topmost surface of a metallic sheet, so anything on top of that must follow any contours of the underlying metal sheet for the readings to be valid.

.... and this is exactly why I have issues with this kind of probe. In early days I installed a sheet of PEI on a glass plate for my printing surface and found out that at higher bed temperatures (IIRC at around approx 90C and higher) the glue sheet lets go and the PEI starts to curl up at the edges. In addition to that, getting an approximation of the surface by scanning the metal underneath does not catch PEI surface irregularities or, more importantly, the occasional air bubble between PEI and glass.
I assume, but have not tested, that both of these issues do not apply to PEI that is directly deposited on spring steel.
The other reason I am still printing on glass is cost - a PEI coated spring steel system can be relatively expensive and is subject to nicks, scrapes or damage from a printhead crash. Setting wrong parameters and getting the print stuck too well on the PEI and you can peel the PEI off the steel substrate.
Float glass is cheap and readily available when you start getting divots on it from too strong adhesion.

R4ffers

@dc42 are there any drawings available please? I'd like to look at making a mount.

deckingman

@jens55 said in Duet 3 Scanning Z probe:

@deckingman said in Duet 3 Scanning Z probe:
As I understand it, your probe will measure the topmost surface of a metallic sheet, so anything on top of that must follow any contours of the underlying metal sheet for the readings to be valid.

.... and this is exactly why I have issues with this kind of probe. In early days I installed a sheet of PEI on a glass plate for my printing surface and found out that at higher bed temperatures (IIRC at around approx 90C and higher) the glue sheet lets go and the PEI starts to curl up at the edges. In addition to that, getting an approximation of the surface by scanning the metal underneath does not catch PEI surface irregularities or, more importantly, the occasional air bubble between PEI and glass.
I assume, but have not tested, that both of these issues do not apply to PEI that is directly deposited on spring steel.
The other reason I am still printing on glass is cost - a PEI coated spring steel system can be relatively expensive and is subject to nicks, scrapes or damage from a printhead crash. Setting wrong parameters and getting the print stuck too well on the PEI and you can peel the PEI off the steel substrate.
Float glass is cheap and readily available when you start getting divots on it from too strong adhesion.

I tend to agree - but with caveats. I have to say that I have no problems using 6mm float glass and I still have the original 3 sheets that I bought several years ago. I do however use 3DLac so some other form of removable print surface might be useful. As you say, powder coated PEI would be preferable to adhesive sheet. But regardless of that, a scanning probe might be useful for tramming the XY gantry with regard to the bed and also for checking the flatness of the (underlying) plate. Any high spots could be scraped or lapped out. That is the approach that I personally would want to take, rather than using software compensation with the inevitable lead screw wear that would result. But that's just me. I've done these measurements before with a DTi but it's a tedious process. So a scanning probe might still be a useful tool, even if the print surface itself is rigid.

T3P3Tony

@R4ffers https://docs.duet3d.com/en/Duet3D_hardware/Duet_3_family/Duet_3_Scanning_Z_Probe#dimensions

R4ffers

@T3P3Tony thankyou

T3P3Tony

@R4ffers the STEP file will go up at some point in the next week or so as well.

gtj0

Hmmm. From the video it looks like the probe has to be mounted "flat" in reference to the bed surface which makes sense but would take up a bit of space. Not that 25mm is a lot but it's "something" . Now if it were a bit bigger, and the center of the coil were open, the hole might be big enough to stick a nozzle through.

Also any limits on the length of the flat FFC cable? My tool platform is very light and I'd prefer not to place the control board on it.

zapta

@T3P3Tony, does the sensor require 'magnetic clearance' around or above it?

Also, is it affected if using individual embedded magnets to hold the removeable bed sheet? (vs adhesive magmatic sheet which has a more uniform static magnetic force).

Notepad

@zapta said in Duet 3 Scanning Z probe:

Also, is it affected if using individual embedded magnets to hold the removeable bed sheet? (vs adhesive magmatic sheet which has a more uniform static magnetic force).

Yes, I believe so.