Parametric Sifting Tray with Replaceable Grate

This is a sifting tray with a replaceable bottom, inspired by Ivestfd's Garden Soil Sifter but re-designed from scratch. The changeable grate means that you can have one box (a ~4 hour print for me) and multiple grates for different applications (~1 hour each on my printer).

I've built something with a similar concept using OpenSCAD to produce a customisable model. The following major changes are introduced:

* Parametric sizing and spacing.
* Use of long "wires" supported in the sides and centre rather than a square grid - will sift narrow objects at their width, not length.
* The "wires" are partially rounded to guide objects through the gap.

Note that put together, this makes it a light duty sifter, not intended for heavy objects. I've uploaded STLs in the default 120x120mm format for each whole mm spacing from 1 to 10, with the thickness of the "wires" tuned to suit the spacing.

You can customise the grating using Customizer, for example to get a spacing for a pa