I needed a bracket to hold a small single-board computer at an angle against the back of a shelf, near a vent, so the thing wouldn't cook itself. The exact bracket for this does not exist, because nobody else has my shelf, my vent and my specific single-board computer in the same awkward arrangement. I spent twenty minutes searching anyway, found three things that were close, ordered none of them, and opened FreeCAD instead.
This is the quiet superpower of having a printer in the house. The question stops being "what can I buy that's nearly right" and becomes "what's exactly right, and how long will it take to make". For a simple bracket the answer is: about half an hour of modelling and an hour of printing, most of which you spend doing something else.
The design itself was nothing clever. A flat back plate with two mounting holes that line up with the shelf bracket already there, a cradle at the angle I wanted, and a couple of ribs so it doesn't flex under the weight. The whole point of a custom part is that you stop compromising. The holes go exactly where my holes are. The angle is the angle I measured, not the nearest one some product designer decided was good enough for everyone. I added a two-millimetre lip so the board can't slide forward and a generous cutout on the underside so air can still move past it, which was the entire reason for the exercise.
A few things I've learned the boring way, which save reprints:
- Measure the real holes with calipers, twice. Print-to-fit guesses cost you an hour and a spool of disappointment.
- Add clearance to holes. A hole modelled at exactly 4mm will not accept a 4mm screw; go 4.3 or 4.4 and stop fighting your printer's tolerances.
- Orient the part so the load goes across the layers, not along them. FDM prints are weakest between layers, and a bracket that snaps along a layer line is a lesson you only need once.
It printed cleanly, the holes lined up first time, which honestly surprised me, and the board now sits exactly where I wanted it with air moving past the bit that gets hot. Total cost a few pence of filament and a Sunday afternoon I was going to fritter away regardless.
The thing I keep coming back to isn't the bracket, it's the shift in what counts as a solvable problem. "There's nothing that fits" used to be the end of the sentence. Now it's the start of one. Not everything is worth designing yourself, plenty of things are cheaper and better bought, but the small, specific, nobody-else-has-this-exact-problem objects are exactly where a printer earns its keep. I didn't buy a bracket. I drew the one I needed, and it fits, because I told it to.