Level 3Unit E · Session 26
26

Unit E · Designing for the real world

Design yours

What we are making: the finished model — a box and a lid, for the device you are actually deploying.

Measure first

  1. The board: length, width, height including the tallest component and any plugged-in cable.
  2. The sensor, and how far it must protrude or how big its window must be.
  3. The mounting holes on the board, if it has them. Diameter and spacing.
  4. Where it is going: what it mounts to, and how much room there is.
  5. Add 3 mm of clearance all round the board inside the box. You will need it.
A 10 mm rod, and three holes drawn for ithole 10 mmwill not fitthe printer over-fillshole 10.4 mmfits, snugly0.4 mm of clearancehole 11.5 mmfits, and rattlestoo much clearanceMelted plastic spreads slightly as it cools, so a printed hole always comes out a little smaller than you drew it.Draw holes about 0.4 mm bigger than the thing going into them. Then measure what you got, and adjust.
Same rule as always: holes oversize by about 0.4 mm, then measure and adjust.

Build it in this order

  1. The outer box: a solid, at the outside size.
  2. Hollow it: a second box, 2.5–3 mm smaller on each side, marked Hole, grouped.
  3. Standoffs: small pillars on the floor so the board sits off it. Match your board's holes.
  4. The cable entry, in the bottom wall. About 2 mm bigger than the cable.
  5. The sensor opening, sized and positioned from your measurements.
  6. A vent, on the underside, if the board will run warm.
  7. The lid as a separate design: a plate with a lip that drops inside the box walls.
📷
images/l3-e2-hollow-box.png
Screenshot: the inner Hole box shown inside the outer solid, before grouping, from an angle
💡 Tip
The lid's lip should be about 0.4 mm smaller than the inside of the box, or it will not go on. This is the same clearance rule, applied to something that is not a hole.
📷
images/l3-e2-lid-lip.png
Screenshot: the lid on its own, lip downwards, with the lip dimension showing

Check it before you hand it in

Against your five decisions from Session 21, and then the printability rules.

What you seeWhyWhat to do
The cable enters through the topWater will follow it in.Move it to the bottom wall. Add a drip loop.
The lid and box are one modelYou will never open it.Two separate files, printed separately.
There are overhangs above 45 degreesThey need support, which is slow and ugly.Chamfer them, or rotate the part.
Walls are 2 mmFine indoors, thin for outdoors.Go to 2.5 or 3 mm.
It takes four hours to printToo big for a shared machine.Thinner walls where it is not structural, or split it into two parts.
No way to mount itTape is not a mounting method for a fortnight.Screw lugs, or slots for a cable tie. Design them in.
⚠ Careful
Print time is a real constraint, not a suggestion. Sixteen teams times four hours is more than a fortnight of continuous printing. Keep yours under ninety minutes and the queue works.

Hand in

  1. Two files: team-N-enclosure-v1 and team-N-lid-v1.
  2. A printed or drawn sheet showing your five decisions and the measurements they came from.
  3. An estimated print time from the slicer, if your teacher has shown you it.
Challenge optional — only if you finish early
  • Design the lid so it cannot be put on the wrong way round.
25. Designing an enclosure