Compatible interlocking bricks two-parameter optimized fit

!!! Just printing the files will fail. Please note the instructions on deleting unused stud/antistud sizes !!!

The challenge in printing interlocking bricks is to get the tolerances right for both studs and antistuds on a given printer, both between layered 3d printed parts and with toy shop "reference" material from injection molds polished to a mirror finish.

And bottom line, 3d printed parts will always show a tighter fit among themselves but that's not necessarily a bad thing - go build crazy, large castles with spanning bridges that would just fall apart in toy shop material.

To easily "dial in" the print process, the files include multiple variants of "studs" (on top of the brick) and "antistuds" (opposite on the bottom side, mating with another brick's "studs"). 

• M should be the starting value, optimal on my Core One in PETG (both 0.4 and 0.6 mm nozzle work well)

• S, XS, XXS shrink by multiples of 50 µm

• L, XL, XXL increase size by multiples of 50 µm

• "shrinking" studs results in a looser fit

• "shrinking" antistuds results in a tighter fit

To use the file, delete all unused variants after importing in the slicer.

Example: Here is how a 2x4x1 brick looks after importing into Prusa slicer:

From trial-and-error I know I need size "M" for both studs and antistuds (this may vary for your printer). 

So I delete all the other sizes and this is what remains for printing:

The picture below shows the "stud" variants in CAD (BTW: note the slight cone angle that prevents an impossibly tight fit between layered surfaces, especially noticeable in 0.6 mm nozzle size.)

The recommended brick size for test prints is 2x4x1. Print two copies. The challenge is sufficiently tight fit with toy store material while still being able to separate two 3d-printed parts.

Note: The smallest sizes 1x1xh and 1x2xh may benefit from slightly larger antistuds as their shell is much stiffer. Don't use them for general tuning

MMU (and in the future: INDX) owners can use colored accents by printing studs / antistuds in a different color.

Hints:

• For large parts in ASA/ABS, make sure XY calibration is set e.g. -0.4 % or the parts won't attach to toy store plates. Z is less critical but check before printing in volume. Ideally, use VLH and print only instances of a single file at a time.

• Single-perimeter looks better

• If studs tear off in use, set infill to 50 % but most importantly use bone-dry filament

• Large plates are easiest in PETG. Bed adhesion in ASA/ABS gets tricky when corners tend to warp upwards.

And, a reminder to parents:

Supervise safe use - with DIY toys, safety is your responsibility. E.g. keep an eye on toy sword that could splinter in nasty ways (PETG I'm looking at you) if overstressed.