I use .8mm PEI ( from Amazon US) clipped to the bed and 100mm+ prints wobble a bit towards the end.
I'll have to glue it soon.
I guess a 3mm thick piece would not budge but you have to raise the bed temp

In the end I've modified Idris's effector to work with Hayden's mag arms at 64mm spacing. He also made some 15mm piezos for me
Pict and details here https://www.thingiverse.com/thing:2361081/#files
I coud only make it work in analog mode on my Duet. VR1 is at 11 and VR2 at 4 o'clock
I'm probing on PEI at 210c hotend (Tested and is fine at 220 for 3 seconds) and 65c bed temp.
Z offset is -0.15 and trigger value 500
Deviation aroud 0.023
This mesh is done on the aluminium plate.

deckingman… I think Idris 3 piezo design could work for you.

Idris... I like your idea better. Lightweight effector and no moving/sliding parts. I went the other way to avoid soldering piezos, something I'm not that good at.
How do you solder to last? And they are connected in parallel I presume?

Presuming a drilled 20mm piezo works just as good as the 27mm one, it should be easy to tune following your instructions

I've been lurking around here for a while now.
I'm with Moriquendi on lifting the nozzle close to the plane of the effector. So I took DjDemonDs 20mm piezo design and made an effector to use with Haydn's magnetic arms. Arm spacing is 64mm, goes with a 30mm fan and a Berd-Air like cooling pipe.
The M3x25 bolts have no thread for the first 6mm at the base and that can make a good sliding zone. There is room for up to 5 but I think 3 will do.
A second Bowden ( http://e3d-online.com/Mechanical/Bowden/Embedded-Bowden-Couplings-For-Plastic-1.75mm-Filament ) can be used to stop the PTFE tube from pulling sideways.

I'm thinking to use it on the Kossel I'm building but that will take a while. Until then here is the link for .stl , .step and .f3d files.
https://mega.nz/#F!z40QRazQ!5OobZxS4iGTfcdOhj_lC3w
If you need them in any other format or modified in any way please ask

Updated 22/04/2017 - Added a second Bowden and made some cosmetic modifications