Piezo decision to make, Bed or Hotend.

snoozer

Hello @ all,

I have recently started to build my own Core-XY printer from the Rat Rig V-Core mechanical kit. There is a different topic in another place on this forum about it. Among a few other things the most pressing decision wise for me is the use of Piezo probe(s). I have thought of alternatives 1st like inductive or IR probes but they all have downsides which rule them out for me. I have been looking around and it seems Precision Piezo from the UK are the go to people to get a working solution. To start with I thought I put one probe in the print head assembly but it may not be the simplest and most room conserving solution for me. I am using a Titan Aero hotend from E3D which rules out the "drilled" type probe due to mounting issues. I would have to put the probe in the mechanical stressed part that holds the entire hotend assembly in place. I am worried I would sacrifice to much mechanical strength and end up with a weak mount. Then I have seen the "Andromeda" type piezos which seem to look ideal for bed mount. Here my actual question to people that have experience with bed mounted piezo probes. I intend to use an Aluminium tooling plate 6 or 8mm strong as print bed and glass or spring steel PEI on top as surface. The bed would be 320x320mm. Would the preload from the weight rule out precise z-probing results ? I understand the trigger comes from the delta between resting and compressed/bend probe, would the delta (or difference) be enough to trigger reliably ? The other question is the movement, on my printer the Z movement is done by the bed. Will the acceleration and decelaration in itself cause issues with false triggering or cause imprecision ? My setup uses a Z max end stop to fast move to a known position with the bad all the way down. From there to home or do bed calibration I would move fast to Z 0 +2-5mm, probe very slow from there.

In short:

Is preloading the piezos an issue (weight of bed)
Are slow moves of the bed on Z acceptable for z-probe precision or are bed mounted piezos only a think where the bed does NOT move on Z ?
Should I rather put the probe in the head while I still have the chance.

Any input, thoughts and suggestions are welcome.

Thanks
Jan

whosrdaddy

Underbed sensing works best when your bed is NOT moving.
So in your case, I would opt for a carriage based solution like the orion or depending on your mount, squeeze the piezo between carriage and gantry like I did here.

snoozer

@whosrdaddy Wow, that works ? Is the mount hollow between the part on the rods and stepper mount or did you just undo your bolts and slide it in and re tighten ?

This is my current mount:
https://www.thingiverse.com/thing:3490910

A plate on the carriage housing the belt tensioner and the actual hotend mount.

Thanks
Jan

whosrdaddy

@snoozer : yes my mount works (and it works very good, I achieve 10µ range), there is a small cutout for the piezo (I believe 0.6 mm if I remember correctly). This allows to have a firm carriage construction as opposed to the Orion for example. Seeing your mount, you can do it like I did on my p3 steel. It took me a bit of time to find a calibration for the precision piezo board, but once dialed in I do not have to touch it...

Alexander Mundy

As to point 1 "Is preloading the piezos an issue (weight of bed)", I have a heavy 400mm diameter bed and with 3 Andromeda it is very sensitive. With Andromeda it is the PCB being preloaded. But moving bed as stated would best be at the hot end due to the same reason of how very sensitive they are. There is a thread at reprap specifically for Precision Piezo with tons of info.
https://reprap.org/forum/read.php?1,767998

snoozer

Thank you both ! I get the idea now how very sensitive they are. I order the Precision Piezo V2.75 PCB with undrilled piezo and an Andromeda and design my hotend mounting for that. The mount is a 3 point mount with 2 bolts at the top and one at the bottom. The Andromeda should be perfect then to be attached to the bottom. I do some testing then how much flex or how little flex I actually need.

I appreciate the feedback.

Jan