Mitochondrion Mark 5.0 progress: the bit that I’m supposed to be good at…

Measure twice, cut once, swear loudly, and measure again like five times…

So one of the goals for the Mark 5.0 is for all the bits just to fit together accurately and quickly. The structure for the Mark 4 was passable but there was plenty of bodging. Instead, the Mark 5 would have a far-more thought out design. So then:

Nice and simple. Aluminium strips, held together by 3D printed nylon bits. The aluminium was rectangular and flat, the 3D printing bits had all the accuracy designed in with lots of location holes. Just tap and screw it all together.


Well, the reality ended up being:

Of those bits, I think one part is correct and usable. The rest is junk. I could call that a waste of several days, or I could think about how much I’ve learnt from trialing this design. Like:

  1. Never try to locate holes by hand if they need to be accurate to within less than a millimetre. Or two. Three on a bad day. Draw up a drilling jig and get it printed in stainless, coz that will cost less than the value of the parts you’ll waste by drilling holes in the wrong place.
  2. Check all the drawings. And then sleep on it and check them again. Coz somehow, a quarter of the pairs of holes that should have been 17 mm apart ended up 14 mm apart.
  3. Tolerances are hard.
  4. Try to avoid designing holes that need three tools to create, especially in aluminium less than a millimetre thick. Also, countersinks really really really need depth stops.
  5. Don’t tap anything when you can just design in a recess to hold a nut.
  6. There may be such a thing as a 40 mm long M2 grub screw, somewhere, but you’re a fool to make a design that needs one.

At least when debugging structure, you can tell if you ballsed it up, coz you screw it all together and it just doesn’t fit.┬áSo yeah, it’s time to design the Mark 5.0.1.

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