u/Trycos79

Disclosure: I work in industrial product-cost consulting. This is a technical discussion, with no service or link.

A wider drawing tolerance may remove a machining or inspection step. But it can also shift cost into assembly, yield, field reliability or supplier variation. The drawing change alone is not evidence of a net saving.

For a proposed tolerance change, I would put four before-and-after checks on one decision sheet:

1. Functional boundary: Which fit, load, sealing or life requirement does the dimension protect? Check the full tolerance stack, not the part in isolation.

2. Process evidence: Compare measured distributions by process and supplier. A better Cp/Cpk after widening the specification does not mean the process itself improved.

3. Real cost movement: Which machining, tooling, inspection or scrap cost is actually avoidable? Which assembly, warranty or sorting risk could increase?

4. Release evidence: What test or production trial demonstrates that the new range still meets the functional requirement, including worst credible combinations?

This is a decision framework, not a claim that wider is always better. ASQ describes process capability as performance against specification limits; that distinction matters when the limits themselves change.

For engineers who have approved a tolerance change: which evidence most often overturned the apparent piece-price saving?

Disclosure: I work in industrial product-cost consulting. This is a technical discussion, with no service or link.

A local cycle-time improvement is sometimes booked as a product-cost saving before anyone checks the whole line. In a multi-step process, the economic effect depends on the system constraint and on conforming output, not just one station's speed.

Before calling it a saving, I would check:

1. Where is the current constraint? Did good units shipped per available hour actually increase?
2. Did first-pass yield, scrap or rework change? Faster nominal cycles can raise cost per good unit if quality deteriorates.
3. Did WIP, queue time or changeover effort move elsewhere? Faster upstream release can simply feed a downstream queue.
4. Which costs are truly avoidable? A change in allocated fixed cost is not automatically a cash saving.
5. Can any freed capacity be redeployed, or will it remain idle because demand or the constraint has not changed?

This is a decision framework, not a claim about a particular plant. ASQ's April 2026 Quality Progress discussion of OEE and TEEP also places equipment metrics in the context of constraints and product mix.

For practitioners: which before-and-after measure has best prevented a local efficiency gain from being mistaken for a system cost saving?