Guides · 23 October 2026
What tight tolerances cost: pricing H7 fits, ±0.02 and fine finishes
Two drawings of the same bracket: one with everything at ±0.1, one with a single Ø12 H7 bore and an Ra 0.8 face. The geometry is identical and the material is identical, so they get the same price. The second one should cost about a fifth more, and the shop that quotes them the same finds out on the inspection bench.
Where the cost of a tolerance comes from
A tight tolerance is not expensive because of the number on the drawing. It is expensive because of four things it makes you do:
- An extra finishing operation. A reamed or bored hole instead of a drilled one, a spring pass, a slower finishing feed for the surface finish.
- A longer setup. Setting the boring head, touching off, a first-off part measured properly before the batch runs.
- Measuring every part. A ±0.1 dimension can be sampled. An H7 bore usually gets a bore gauge or plug gauge on every part, and someone has to do it.
- More scrap. The tighter the band, the more parts fall outside it from tool wear and temperature. Plan for it, or it comes out of the margin.
A worked example
An aluminium bracket, 50 off. Machine A$120 an hour with its operator, inspection labour A$65 an hour, A$7.50 of material per blank, 10% overhead and 25% margin on cost.
| All ±0.1 | With H7 bore and Ra 0.8 | |
|---|---|---|
| Setup | 60 min | 80 min |
| Cycle per part | 6.0 min | 7.2 min |
| Inspection per part | 0.2 min (sampled) | 1.0 min (every part) |
| Good parts planned | 97% (52 blanks) | 93% (54 blanks) |
| Unit price | A$31.49 | A$38.42 |
The difference is A$6.93 a part, 22% of the price. Split by cause, per part including overhead and margin:
| Cause | Adds per part |
|---|---|
| Finishing pass (1.2 min more cycle) | A$3.43 |
| Scrap allowance (2 more blanks, run and inspected) | A$1.20 |
| Measuring every part | A$1.19 |
| Longer setup (20 min) | A$1.10 |
None of these is large on its own, which is why they are easy to leave out. Together they are most of the margin on the part.
What to look for on the drawing
- Fits: H7, H6, g6, k6 and the like on bores and shafts.
- Tolerances of ±0.02 or tighter, or a total band of 0.04 or less.
- Surface finish of Ra 0.8 or finer: below that you may be grinding, honing or lapping, which is usually outside work.
- Geometric tolerances: tight flatness, position or runout often decide how the part has to be held, not just how it is cut.
- The general tolerance block: a title block that says ±0.05 unless stated makes every dimension tight.
Ask before you price it
Many tight tolerances are copied from an old drawing or set by a default in the CAD template. A short question, "is H7 needed on the Ø12, or would ±0.05 do?", costs nothing, and buyers often agree. If they do not, you have a reason for the price that you can show them: the finishing pass, the gauge, the scrap.
Spindlewise reads PDF and scanned drawings attached to a quote and lists the fits, tolerances of ±0.02 or tighter, Ra 0.8 or finer finishes, threads and heat treatment it finds, next to the attachment, so they are in front of you while you build the routing. The extra operation, setup and inspection time and the yield go into the quote like any other line, and every price shows the cost behind it.