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Minimum Wall Thickness Calculator with OD, ID and Concentricity

The thinnest point of a bored part depends on more than the drawing wall dimension. Outside diameter limits, bore limits and how far the bore axis sits from the OD axis all remove material from one side. This calculator puts them together.

Your numbers

mm
mm
mm
mm
mm

Position or coaxiality tolerance of the bore to the OD axis, diametral zone.

mm

Your results

Worst case minimum wall
4.875
Smallest OD, largest bore and the full axis offset on the same side.
Margin against required wall
0.375
Nominal wall
5
Maximum wall on the thick side
5.125
Wall thickness variation (thin to thick)
0.25
Meets requirement (1 yes, 0 no)
1

Worst case arithmetic. For high volume parts a statistical (RSS) treatment of the contributors will predict a larger typical minimum wall.

Save results:

Worst case minimum wall vs coaxiality zone (mm)

Sweeps Coaxiality zone (diameter) from 0 to 1, holding your other inputs fixed.

Automate pre-release tolerance checks

Optional: a short review of adding stack and wall checks to your engineering change workflow.

Optional. The tool and every export work without this. No spam.

How to use it

Enter nominal OD and bore, each with a plus or minus tolerance, then the coaxiality or position zone relating the bore to the OD axis. Add the minimum wall your design needs for pressure, stiffness or machining. The tool shows nominal wall, worst case minimum, worst case thick side and the margin. The chart sweeps the coaxiality zone to show how fast a loose control eats wall, which often justifies tightening a position tolerance instead of widening the size tolerances.

Formula and logic

The wall on one side is half the difference between OD and ID, reduced by the offset of the axes. An axis offset equals half of the diametral coaxiality zone. At the thin side, the wall is (OD minimum minus ID maximum minus zone) divided by 2. For 50 +/-0.10 and 40 +/-0.05 with a 0.10 zone, that gives (49.90 minus 40.05 minus 0.10) over 2, which is 4.875 mm against a nominal wall of 5.000 mm.

  • OD low and bore high both thin the wall by half their tolerance each
  • The coaxiality zone is diametral, the offset is half of it
  • Roundness and form errors add further local thinning
  • Eccentric tube stock needs extra allowance

Common mistakes

The usual mistake is treating the zone as a radius and subtracting too much or too little. Another is checking wall thickness only at nominal sizes and finding that a part passes on paper but fails by the stack of tolerances. For plastic and cast parts add draft and core shift. For tubing, the supplier tolerance on wall already includes eccentricity, so do not double count it. If the answer is negative or close to the requirement, consider tightening the bore position, switching to a profile control, or specifying wall thickness directly.

Frequently Asked Questions

Is concentricity the same as coaxiality?

Not exactly. Current ASME Y14.5 uses concentricity for median points, a rarely needed control, while coaxial features are normally controlled with position or runout. Here the zone means the diametral zone for the bore axis relative to the OD axis.

Why does the coaxiality zone matter so much?

Because it shifts the bore toward one side of the OD, and the thin side loses half the diametral zone. A 0.5 mm zone can remove 0.25 mm of wall on one side, more than the combined size tolerances.

Should I use worst case or RSS here?

Worst case is safe for critical pressure or safety parts and for low volumes. RSS is acceptable when the contributing processes are independent and capable, as it shows a more realistic minimum for large production runs.

Does this include roundness error?

No. Out-of-roundness and taper reduce wall further at local points. If the drawing does not limit form separately, size limits under the envelope principle limit it, otherwise add an allowance.

If wall thickness checks are done after the fact in your ERP quality module, Netray can help build a pre-release check from your drawing data.

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