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Keyway dimensioning

Keyway dimensioning

(OP)
Hi All,

I am designing a part that has two keyways 180 degrees apart on a single large diameter shaft. The intention of the keys/keyways is to allow axial motion of a female sleeve to which the keys are mounted while preventing rotational motion. It is desired that there is a minimum amount of rotational play.

What is the best way to tolerance the keyways and keys?

Thanks in advance.

RE: Keyway dimensioning

cobra 46: Might I suggest attaching a sketch that the forum could critique.

Certified Sr. GD&T Professional

RE: Keyway dimensioning

cobra46,

The most common method I've seen is a combination of size (width) and position. The width tolerance controls the size and form of the keyway, and the position tolerance controls the location and orientation of the centerplane (usually with the axis of the shaft OD as the datum feature). See Fig. 7-31 in Y14.5-2009 - the slots are not exactly like keyways but the tolerancing is similar.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Keyway dimensioning

cobra46,

Might I also recommend looking at figures 4-17 and 4-40 in Y14.5-2009 for other examples; however, I don't recommend "0" positional tolerance.

Certified Sr. GD&T Professional

RE: Keyway dimensioning

This will probably open a can of worms, but anytime an MMC modifier is used, a zero should be considered. There are actually few reasons to not use a zero. The main one is that it might not be understood (that's not the GD&T's fault) and another reason might be if you're concerned about mass or weight. Other than that, to not use a zero is usually cheating yourself out of tolerance.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

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