Precision Piezo 20mm disc to LM8UU bearing mount

thingiverse

Edit 8/13/2018: So... I actually built and tested this. I deprecated the long version, as the small one is plenty strong enough, and has more than enough advantages to decide not to need the long version. A couple of problems that I've addressed in the new version: Using the 4 screws to hold the whole assembly together puts the stress of holding the bearings on the piezo disc. If your printer didn't make this exactly to dimensions, or if your LM8UU bearings were slightly larger than spec, this results in a lack of sensitivity. It can still be tuned, but I'm not sure about longevity of the setup that way, and I don't want to introduce any slop in the bed mount. Solution: Make 2 of the holes in the plunger piece larger, to allow the socket head cap screws to float. These can be tightened to keep cap pressure on the bearings, while the other 2 hold the entire assembly together. This is only possible on the small version and was the major deciding factor for deprecating the large version. Using 2 screws to mount the assembly to the bed was excessive, and not necessary. A single screw at leach location is more than adequate to prevent lateral motion of the bed particularly if it is mounted tightly, as intended. A single screw CAN also allow a spring tension height adjustment for levelling, though I am not certain what this will do to sensitivity. (PIezo discs are very sensitive, so this might still work, but result in more possible false triggers.) Solution: move the mount screw to the center of the plunger. Certainly you could opt to just use one of the 2 screw locations from before, though this would be unbalanced if you were to opt for the spring mount. It was possible to mount the system so that the disc was already at the allowed maximum motion. This is a combination of factors, including the first issue addressed by making the 2 screws float. I increased the depth of the opening, to allow for more flex in the piezo disc, and increased the height of the plunger by 0.25mm. This should not damage the pieze ceramic in the event that the plunger is pressed fully to the disc mount cup, but does allow for a little more adjustment range. Original description follows: Mounting system for heated bed. you will need 3 of these (Though I see no reason you couldn't use 4, you should only need 3) 2 versions included, one is 30mmX50mm, the other is 30mmX30mm. This might be a little weaker, as the screw holes are closer to the actual bearing opening, but will save a little space. Each set holds one 20mm piezo disc sensor. A plunger piece is mounted to your bed via 2 screws spaced at 40mm. The plunger piece should hold 2 standard 3mm nuts (5.5mm wrench size) Each set has 4 pieces. An upper and lower "cap" piece to hold the LM8UU bearing. The lower cap will hold 4 3mm nuts. A bed to hold the 20mm piezo disc goes on the upper cap, and then the plunger should take a set of 3mm screws into it. The whole assembly will then have the disc and the LM8UU bearing sandwiched into it and have a slight pre-tension applied via the 4 screw/nut combinations holding it together. The mounting deck should be between 21.5 and 22.5mm from the centre point of the LM8UU bearing, with some slight allowance for the piezo disc itself. I set up my drive axis to assume 22mm between mounting deck and rod centres. The upside to this is that automatic bed leveling should be easy as pie. The downside is that this leaves practically nothing for making adjustments. The piezo disc itself is some 9mm away from the bed material. This along with whatever mounting strata should insulate it from the heated bed adequately for function. This is a work in progress. I'm publishing this here as an addemdum to my beltless printer design, since I had to redesign the bed mechanism anyway, and I want to implement the Precicion Piezo sensors anyway, it seemed like a good idea.