The email arrived at 11:20 on a Tuesday morning, day three of an eighteen-day run.
One hundred and twenty pneumatic manifolds for a customer in Ohio. 6082-T6 aluminum, 148 × 92 × 46 mm, nine ports, two faces milled flat to 0.02 mm, clear anodised. We had quoted USD 68.40 a part and started cutting on the Friday. Forty-one blocks were through the first operation. The message was two lines long: port 4 moves from Ø12 H7 to Ø12.5, and it moves 3 mm sideways to clear a hose that had changed.
We stopped the machine at 11:26.
Why the stop is not negotiable
Every part that comes off the machine after a revision is a part you may have to write off. Forty-one blocks existed when the email landed. If we had kept running while the customer’s design team argued about the new position, we would have added about fourteen parts an hour to that number. The revision meter runs at the speed of production, not at the speed of the order value, and that is the part people get wrong when they guess what a change will cost.
Six minutes between the email and the spindle stopping is the only reason this story ends with a number instead of an argument.
What the revision actually cost
Here is the reconciliation we sent four days later. It is not a penalty and there is no markup on it. It is hours and material.
| Item | Basis | USD |
|---|---|---|
| 41 blocks scrapped at rev A | USD 9.20 material + USD 14.60 machining per part | 975.80 |
| CAM rework | 3.5 h to re-post op 1 and re-sequence op 2 | 217.00 |
| New drill jig plate | Plate, bushings, 2.0 h of tool room time | 464.00 |
| Extra setup and first article | 3.7 h across two shifts | 229.00 |
| Weekend shift to claw back three days | Two operators, Saturday | 254.00 |
| Total | 2,139.80 |
One note on the first line, because it is the line customers question. We value scrapped work in progress at what it has actually cost so far — material at our purchase price, plus the hours that part has already been through — not at the finished part price. Forty-one finished manifolds would have been USD 2,804. Forty-one blocks through one operation were USD 975.80. Charging the difference would be charging for work nobody did.
About USD 18 per part on a 120-piece order. Had the same revision arrived on day one — before setup, before the jig plate was cut — it would have cost USD 681: the CAM work and the new jig, no scrapped material, no recovery shift.
And on a 1,000-piece order the fixed half of that bill would be identical. The CAM hours do not change. The jig plate does not change. What scales is the forty-one.
Three ways to make a revision cheaper
None of them need anyone to be clairvoyant. They need a decision about when the drawing freezes.
Freeze it before the first chip. We ask for a signed drawing 24 hours before setup and we do not start cutting without it. That window is free, and it exists because once op 1 is programmed and the soft jaws are cut you have spent the money whether or not a single part is finished.
If something is going to move, let it move before the second operation. A revision that only touches features created later costs the programming and the setup and nothing else. On this job, op 1 was CNC milling on both faces and the datum bore; all nine ports came in op 2. Moving port 4 on day one, after op 1 and before op 2, would have taken the scrap line to zero and the bill to about USD 900.
Mark the features you are least sure about. Interfaces change. Mounting holes, port positions, cable clearance — anything that has to line up with a part somebody else is still designing. Those are the features that generate revisions, and they are also the ones you can leave at nominal until the design settles. A note on the drawing that says “port positions to be confirmed at PO” costs nothing and has saved more than one customer a five-figure write-off.
What we did with the forty-one
They did not go in the bin. Twenty-six were reworked: the Ø12 H7 bore was reamed out to Ø12.5, which is legitimate because the new position was 3 mm away and the larger bore still sat inside the new boss, and the milled faces still met the rev B print. The other fifteen had the old port too close to a boss wall to take the bigger bore, so they went back to the customer as service-kit spares.
That decision is worth making out loud rather than by default. An oversized port on a manifold is usually recoverable. A bored bearing fit is not. We ask before we scrap anything, and we send photographs of what we are proposing to rework.
What it means for your next RFQ
On a pilot build or a first article, assume the drawing will move. Put a hold point in the schedule: one conversation before op 2 where you look at what has actually been cut and confirm the interfaces once more. It costs a phone call, and it is the cheapest insurance on the order.
Our RFQ checklist covers the drawing freeze and the revision process along with everything else we need up front, and the cost breakdown page shows what the per-part figures above are actually made of. For a number on your own part, send the drawing through our instant quote page or straight to our team — we confirm within one business day. Material pricing moves with the market, so read the material figures here as a budget estimate based on our latest purchase price rather than a fixed rate.
The revision was not the customer’s mistake. Shipping a manifold that does not reach the hose would have been. The only thing worth arguing about is when the change happens, and that gets decided by whoever picks up the phone first.