GD&T Virtual Condition and Resultant Condition Calculator
Virtual condition is the worst case boundary a feature of size can create when its size and its geometric tolerance combine at their worst. Mating parts assemble if their virtual conditions do not collide. This calculator does the sums for a pin and hole.
Your numbers
Diameter zone from the feature control frame.
Your results
Applies when both features use the MMC modifier on position and the datum references are not subject to shift. This is the fixed or floating fastener logic in simplified form.
Guaranteed clearance vs hole position tolerance (mm)
Sweeps Hole position tolerance at MMC from 0 to 0.2, holding your other inputs fixed.
Review gauge and tolerance data
Optional: a short review of how gauge sizes and tolerance data are held against released drawings.
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How to use it
Enter the pin size limits and the hole size limits, plus each position tolerance as it appears in the feature control frame with the MMC modifier. The tool returns each virtual condition, the guaranteed clearance, and the resultant conditions that describe how loose the assembly can become. The chart sweeps the hole position tolerance so you can see how much clearance you trade when you open that tolerance for the machine shop.
Formulas
For an external feature such as a pin, virtual condition is the MMC size plus the geometric tolerance. For an internal feature such as a hole, it is the MMC size minus the geometric tolerance. Resultant condition is the opposite extreme: LMC size minus tolerance for a pin and LMC size plus tolerance for a hole, once bonus tolerance is fully used. Guaranteed clearance is hole VC minus pin VC. If that is zero or more, every part assembles.
- Pin VC = MMC + position tolerance
- Hole VC = MMC - position tolerance
- Pin RC = LMC - tolerance, Hole RC = LMC + tolerance
- Fixed fastener: hole MMC minus pin MMC at least equals the sum of both tolerances
Notes and mistakes
Virtual condition assumes the MMC modifier. With RFS the boundary does not change with size and the maths differs. In the floating fastener case the tolerance is split between both parts, while in the fixed fastener case the pin is attached to one part and the sum of the two tolerances must fit the clearance. Functional gauges are built at virtual condition, so a poor calculation leads to wrong gauge sizes. Lastly, datum feature shift can add extra movement that this simplified tool does not include.
Frequently Asked Questions
What is virtual condition in GD&T?
It is the boundary generated by the collective effect of a feature size's MMC and the geometric tolerance applied at MMC. For a pin it is MMC plus tolerance, and for a hole it is MMC minus tolerance.
What is resultant condition?
The worst case boundary of a feature when it is at LMC and the full geometric tolerance, including bonus, is used. It describes the loosest condition and is used to compute maximum gaps.
How do I size a functional gauge from this?
A fixed gauge pin or opening is made at the virtual condition of the feature being checked, with a small gauge tolerance. A part that fits the gauge also meets its size and position limits together.
Does a positive clearance guarantee assembly?
Yes for these two features, when both are at their worst case and use MMC. Other effects such as datum shift, form errors, coating or burrs are not included, so confirm them separately.
If gauge sizes and drawing tolerances are tracked in your ERP or PLM, Netray can help cross-check them against released drawing data.
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