A mislocated but critical feature can cause assembly delivery delays, quality holds, rework, expediting, and line stoppage. The consequence is not just the machining cost. It is the cascade.
One bore looks trivial on a drawing.
In production, it can be the stumbling block feature in the whole part.
I’ve seen teams spending weeks on which machine to choose, spindle hours, even coating.
Then one bore comes with a slight drift off, and everything in next steps starts throwing money in fire.
The pin won’t enter cleanly.
The shaft fights against assembly.
The bearing loads unfitting.
The fixture gets at a slant.
Inspection gets messed up.
Production haults for finding problem source.
Then someone says the line has to wait.
That’s the moment the drawing stops being a drawing.
This is why I draw your attention to bores very differently from how many RFQs describe them.
A bore is rarely just a hole.
It is usually one of these things:
a locator
a load path
an alignment feature
a stack-up amplifier
a hidden assembly risk
And if it is any of those, the real question is not:
“Can we machine this bore?”
But an actual question is:
“What happens to the whole system if this bore drifts?”
That is where a lot of quoting ignores.
If the bore controls alignment into an assembly, a few microns in the wrong direction can do more damage, that’ even impactful than a visibly ugly cosmetic surface for the part.
Because cosmetic defects trigger emails.
Functional bore defects trigger stoppages.
Siemens reported downtime costs in automotive at $2.3 million per hour in its 2024 downtime analysis. Even SMEs can pay it up to $150,000 per hour.
So no, I don’t look at a critical bore and think about cycle time first.
I think about:
- assembly force,
- coaxiality and position relative to the real datum structure,
- inspection method,
- wear over volume,
what happens at 500 parts, not only at part number 5?
A lot of high cost problems start as “the hole was only a little off.”
Such saying has probably wasted more financially than most admit.
If you’re reviewing a part right now, look at the one bore nobody is worried about.
That’s often a source that ends up holding the meeting.
