AluExt 20 - Aluminum Extended

while i tinkered with aluminum extrusions a bunch of times, recently i went through with three individual projects using them. in the process i kind of created a framework / library by accident. this happened i think because all three of those projects didn't have an exact plan on how the finished structure would look like in the end. and since i ended up adjusting as i went having the flexibility during that process i tried to solve similar problems in those projects in parallel.

the workflow that worked very well for me was: 
* print a bunch 1 by 2 corner blocks
* start screwing stuff together
* come across one connection that can't be done with the default block
* print one or two of the other blocks
* repeat
* come across one connection that can't be done with any of the blocks
* create a new block based on the default one
* repeat

current tested defaults:
20x20 aluminum extrusions slot 6mm, lengths: 0.2m, 0.3m, 0.5m, 1m
M4 x 20mm hex socket screws
12mm washers

questions i would have:

why not use standard alu extrusion corners / brackets / plates?
- when you start planning often you dont know the exact number of parts. with aluext you can print as you go
- most standard corners only allow for right angled butt joints. by having the two screws of a corner not on the same plane the extrusions can be mounted at an angle to each other.

why the default extrusion length?
- for one you can order them directly in those length and therefore dont need to cut anything
- and two: even if you do cut them yourself, they dont need to be exact, since they almost always overlap each other. because of that the extrusion itself doesn't have to be the length of the critical dimension of your application

why washers?
- it felt like the screw head would dig too much into the PLA. so washers seemed the way to go. maybe countersunk screws work as well

are 3d prints strong enough?
- for most stuff, probably. also: if one 3d printed block seems too flimsy, add another. depending on the joint you could use four block and eight screws to increase strength. or start printing in stronger materials and/or more perimeters

why countersinks on both sides?
- i had a left and right piece at first and it was too annoying to try to find the other one almost all of the time. also sometimes i noticed multiple ways to make use of the same block because of it

what about 30x30? 40x40?
- yes. untested as of yet but the whole thing is parametric. so i created the files already

where's the source? examples?
- https://github.com/ben-gineering/aluext