GTOL Rule #1

#414 / Mechanical Engineering Easy

For the pin shown, answer the following questions:
  1. According to Rule #1, also known as the limits of size, the size tolerance applied to a feature of size controls what?
  2. What is the max amount of bow allowed on the pin?
  3. If the pin were produced at a diameter size of .399, what is the max form variation allowed?

Expand Hint
Per ASME Y14.5, Rule #1 is:
“Where only a tolerance of size is specified, the limits of size of an individual feature prescribe the extent to which variations in its geometric form as well as size, are allowed.”
Hint 2
The feature’s form may vary within the size limits. At MMC, the form must be perfect. As the it drifts from MMC to LMC, the feature may be more bent, tapered, or out of round. This guarantees fitment at the next level assembly.
The limits of size (Taylor Principle, Envelope Principle, Rule #1) defines the form and size limits of individual, regular features. For most common situations, it requires perfect form at Max Material Condition (MMC) to ensure a component will fit inside an opening. Per ASME Y14.5:
“Where only a tolerance of size is specified, the limits of size of an individual feature prescribe the extent to which variations in its geometric form as well as size, are allowed.”
The feature’s form may vary within the size limits. At MMC, the form must be perfect. As the it drifts from MMC to LMC, the feature may be more bent, tapered, or out of round. This guarantees fitment at the next level assembly.
Thus, Rule #1 controls size and form. To find the max bow allowed:
$$$.399-.396=.003$$$
Since .399 is the MMC, then the form must be perfect. So, the max form variation allowed is: .000
  1. Size and Form
  2. .003
  3. .000


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