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Do I machine a bore bigger or smaller before plating?

Last updated 10 August 2026

Bigger. A .375 bore at plus or minus a thousandth, plated .0002 to .0005 per side, has to be machined to .3750 / .3764.

This is the one people get backwards, and it is expensive when they do. Plating adds material to whatever it lands on. On an outside diameter that makes the part bigger, so you start small. Inside a bore the coating grows inward from the wall and closes the hole, so you start large.

Same coating, opposite correction. A spreadsheet that subtracts everywhere is wrong on half the features of any part that has both a journal and a hole on it.

Worked

On the print	.3740 / .3760 in
Process	Plating
Per side	0.0002 to 0.0005 in
The dimension gets	smaller at this operation
Pitch diameter shift per unit of per-side effect	2 times
Hold before the process	.3750 / .3764 in

The process range costs .0006 of tolerance upstream, because the part has to be in specification whichever value the process lands on.

Open this case in the calculator, and change the numbers.

Computed by ctrlPlanner. MIL-STD-870, Federal Screw Thread Specification H28.

This is one characteristic. A real part has forty of them through five operations, and every one needs the same walk when the drawing revises. That is what ctrlPlanner does from a ballooned print.

Open the demo · a print is already loaded, no sign up.