While putting together the exterior extrusion frame for Luggable PC Mark II Revision B, I got frustrated with another recurring headache. Aluminum extrusions (like the 15mm Misumi HFS3 I’m using) are shaped so I could put fasteners (in this case, standard M3 nuts) in a rail to fasten things at arbitrary locations along the extrusion. The fact the nuts can slide anywhere along the rail also meant they don’t stay still. If I place the nuts at the desired locations, I have to be careful not to bump or tilt the assembly or the nuts will go sliding out of position.

After too many episodes of nuts moving out of place, I decided to put some thought into the problem. I ended up with a small 3D printed part I can insert into the extrusion along with the M3 nut. It is large enough to rub against the edge of the rail and thereby holding the M3 nut in place, but small enough that it can still be moved with a little push.

It was a challenge to dial in the exact dimensions. The acceptable range is very narrow – in fact almost too narrow for a consumer-level 3D printer like mine to handle. Within the same batch I printed, some are extremely tight and some are too loose. If I print at a different time of day, some are entirely unusable. I also ran out of one spool of filament during a print, and the new spool (even though it is the same type from the same vendor, probably even the same manufacturing batch) returned different results.

So I have to keep adjusting dimensions and generate different files between batches. Fortunately, since they are small, it is not a huge loss of material to just throw away the unusable pieces. It solves my headache and that’s all I really ask of them.