Under-mount build plate holder

We all end up with multiple build plates sooner or later, right?  I got sick of leaving mine propped up against the wall and the storage options I found through a quick search of Printables either took up bench space or were more complicated than I needed.

My solution has only two pieces and is designed to be printed without supports and to be easy to install.  While the dimensions are to suit the build plates of a Bambu Labs A1, this also uses a plate as a setout template for installation, so if your printer's plate size is close to that of the A1 then this should work for you out of the box as the mounts will end up spaced to suit your plate.  I've also included *.step files for ease of tweaking if your requirements are significantly larger, smaller or thicker.

Printing tips:

• Print the model with the slots oriented up - no supports are needed this way!
• The files contain the right hand mount only, so mirror it in your slicer to generate the left hand mount
• Print at 0.2mm layer height
• I printed mine in PLA with 3 walls and 15% infill and they seem robust enough

Installation - I promise it's pretty easy as long as you don't attempt to take terrible photos while you do it:

1. Clamp a build plate to the underside of your shelf/desk/bench, making sure it's in the desired location and you've left enough space around it to install the mounts (around 30mm for the 4-slot version)
2. Mark lines around the sides and back edge of the plate with a pencil
3. Remove the build plate and, using the super-handy notched edge of one of the mounts as a ruler, set out the centres of the mounting screw holes along the side pencil lines from the datum of the rear pencil line
4. Drill the holes in the four mounting locations, being careful not to drill right through the shelf/desk/bench
5. Screw the mounting screws in most of the way.  This is designed for a 6-gauge countersunk screw, but if that size isn't familiar to you (honestly, I've no idea why my otherwise-metric country uses gauge sizing for this) you're looking for a screw that slides snugly into a 3.8mm-ish hole.
6. Push the mounts onto the screws via the large ends of their screw holes, then slide the mounts toward each other.  They should need firm, but not violent, pressure to make them move.  If they don't slide, remove them from the screws, loosen the screws a little bit and try again.  If they move too easily or don't sit snugly against the mounting surface, remove them from the screws, tighten the screws a little bit and try again.
7. Check that a build plate sits flat in the slots - if not, give the mounts a little tap sideways to move them further apart
8. (Optional) drill two more holes for screws to lock the mounts in place