DEMO — fictional range. Local brief only, NOT SENT. No personal data is collected or transmitted.
GUIDE
The order the questions are worth asking in.
This is the sequence a machining programme follows when it goes well, and the point at which each step becomes expensive to revisit.
- 1 · The assembly
- What the part fits into, because that decides the datum
- 2 · The datum
- Named on the drawing, reachable with an instrument
- 3 · Material
- Chosen for the load and the environment, then for machinability
- 4 · Heat treatment
- And whether it happens before or after finishing
- 5 · Features
- Which dimensions locate, which carry load, which are only clearance
- 6 · Tolerance
- Set from the first five, not copied from an earlier drawing
- 7 · Setups
- Designed so the critical feature shares a setup with the datum
- 8 · Inspection
- What is measured, from which reference, by whom, and what happens if it fails
Why the order matters.
Each step constrains the next. Choosing a tolerance before the datum is choosing a tolerance for a dimension whose meaning has not been fixed, and choosing a process before the tolerance is choosing a process for a part nobody has specified.
Where programmes usually go wrong.
Step two, left to the shop. It is the cheapest step to do properly and the most expensive one to inherit.