Read a part drawing
One complete print, five questions about it. Some answers are on the drawing, some you have to work out. Get 10 right to finish.
Same drawing, question 1 of 5
What position tolerance do the holes get when they are at their smallest size (MMC)?
What is on the drawing
- Two views: the front view with the holes, and the top view with the thickness. The projection symbol in the title block tells you where the top view goes.
- Dimensions: the edge distance, the hole spacing (like 2X .750), the overall length, the height with its own tolerance, and the thickness.
- Hole callout with a feature control frame for position at MMC to datums A, B and C.
- Surface finish on the top face, and the title block with material and general tolerances.
Distances that are not dimensioned
Good drawings do not repeat dimensions, so some distances you have to work out. The distance from the last hole to the right edge is the overall length minus the edge distance minus the hole spacing.
Questions
- Where do I find the tolerance for a dimension without one?
- In the title block. US drawings give a tolerance per number of decimal places. European drawings refer to a general tolerance standard such as ISO 2768-m.
- What does 2X .750 mean next to a row of holes?
- Two equal spaces of .750. With three holes, the first and last hole are 2 x .750 = 1.500 apart, center to center.
Explained in our own words and checked against several textbooks and published tables. For the full rules, see ASME Y14.5, ASME Y14.36, ISO 286, ISO 965, ISO 1302 and ISO 21920-1.