GD&T is a means of dimensioning & tolerancing a drawing which considers a size feature contains the maximum amount of material within the stated limits of. In GD&T, maximum material condition (MMC) refers to a feature-of-size that contains the greatest amount of material, yet remains within its tolerance zone. Effective Training Inc - Your Source for GD&T (Geometric Tolerancing) Materials and Training.
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If additional dimensions would be helpful, but are not required, they may be marked as reference.
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Dimensions should be applied to features and arranged in gd t material a way as to represent the function of the features. Additionally, dimensions should not be subject to more than one interpretation.
Gd t material of manufacturing methods should be avoided. The geometry should be described without explicitly defining the method of manufacture. If certain sizes are required during manufacturing but are not required in the final geometry due to shrinkage or other causes they should be marked as non-mandatory.
All dimensioning and tolerancing should be arranged for maximum readability and should be applied to visible lines in true profiles. When geometry is normally controlled by gd t material sizes or by code e.
Unless explicitly stated, all dimensions and tolerances are only valid when the item is in a free state. Dimensions and tolerances apply to the length, width, gd t material depth of a feature including form variation.
Maximum material condition comes in handy when it comes to making a functional gauge for the part. For example if you wanted gd t material ensure that a pin always fits into a hole when the hole is at MMC, we could design a pin gauge that mimics the lower limit of the hole.
The gauge pin would then be inserted gd t material the hole and as long as the pin Goes into the hole, the part is in spec.
For example, you have a pin with a dimensional and perpendicularity call outs. In this case all you really care about is the pin fits into the hole at the worst case limits MMC and max perpendicularity tolerance make up the maximum envelope of the part The gd t material condition can be controlled with a functional gauge.
Let's take a deeper look into the different types of material conditions that can be gd t material to tolerances.
As the image above shows there are four different material gd t material that can be applied and each gd t material behaves differently than the others. This is the implied condition. All tolerances apply at RFS by default, which means no symbol is needed.
This provides a feature with additional geometric tolerances as the feature's size departs from its maximum material conition.
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Behaves just like the MMC. The differences will be discussed later on.