Common fitting assignments of the first year and how to make them to ±0.04 mm accuracy.
In the fitting section the trainee makes pairs of parts that fit each other. These jobs develop accuracy in marking, sawing, filing and measuring.
Common fitting jobs
| Fit | What it is |
|---|---|
| Square fit | A square male piece fits into a square opening of the female piece in all positions. |
| Sliding fit | The male part slides smoothly in the female part without shake. |
| Step fit | Steps of the male part fit the steps of the female part. |
| Angular (dovetail / V) fit | Angled faces (e.g. 60°) fit together; checked with a bevel protractor. |
| T-fit | A T-shaped male piece fits a T-slot. |
Accuracy Typical first-year fitting jobs are made to ±0.04 mm and should fit with interchangeability – the male part fits even after turning it over (180°).
Sequence of work
- Check the raw material size; file and finish two datum faces at 90°.
- File the other faces to size, parallel and square.
- Apply marking medium; mark out from the datum faces with a vernier height gauge / odd-leg caliper.
- Punch witness marks; drill relief holes at inside corners.
- Remove the waste metal by sawing and chipping.
- File close to the lines; finish with a smooth file, checking with vernier, micrometer, try square and bevel protractor.
- Make the male part first, then file the female part to suit it.
- Check the fit; remove high spots with care.
- Deburr all edges.
Tip Never "force" a fit with a hammer. Use Prussian blue on the male part to see where the female part is tight.
Quick Revision
- Fits: square, sliding, step, angular, T.
- First-year accuracy ±0.04 mm.
- Work from datum faces; make male first, then female.
- Drill relief holes at inside corners.
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