GD&T for a groove machined in a flat surface
GD&T for a groove machined in a flat surface
(OP)
Which GD&T would be best for control. Profile of surface or True Position with Boundary?
Richard D. Postak
Aerospace Mechanical Designer
Schafer Corporation





RE: GD&T for a groove machined in a flat surface
Profile of surface locates your groove from the datums. True position allows you to locate a feature of size. Probably, the true position is very much less critical to you than the size of the feature. I cannot see why I would accurately locate a sloppy feature of size, but maybe you have a good reason.
What are you trying to accomplish?
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JHG
RE: GD&T for a groove machined in a flat surface
Oops! That is not true. I love to locate wildly inaccurate holes to zero position at MMC/B.
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JHG
RE: GD&T for a groove machined in a flat surface
Equally vague answer: Whichever one best suits the designed necessity of the feature.
Less-sarcastic-answer: Grooves can vary a lot. Are we talking about a groove for an o-ring? Are we talking about a groove to let gravity drain fluid out of a stationary object? Or is it a groove that will allow material from an adjacent member to be staked/deformed into it to resist fastener walking?
One application may require tight profile control in both location and form. Another might not care about size, but the position matters. Another might not so much care about location, but size is more important. Sorry for the non-answer.
RE: GD&T for a groove machined in a flat surface
No worries and all good questions, however I am not the designer just the checker and still sort of new at it. I will ask the designer on the intent of the groove and go from there.
Thanks!
RE: GD&T for a groove machined in a flat surface
RE: GD&T for a groove machined in a flat surface
Your datums look weird to me. I am glad I don't have to inspect this. Since I don't know how you will use the part, I am saying weird, not wrong. Try to work out your fixturing, given that your primary and secondary datum feature are FOS holes, and the bottom face is your tertiary datum feature.
I take it your slot wraps around the end? As per ASME Y14.5, your specification is meaningful. I cannot see what you are trying to do.
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JHG
RE: GD&T for a groove machined in a flat surface
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: GD&T for a groove machined in a flat surface
RE: GD&T for a groove machined in a flat surface
I am still trying to understand your fixture. You have an accurate rod (Ø.0604/.0602?) to pick up datum face A. This controls X, Y, and two axes of rotation. You have a diamond pin that picks up two sides of datum face C, but clears the bottom of the hole. This controls the other axis of rotation. You have a flat face that picks up datum face B, and controls Z. Note how the flat faces contact at one point, only. There is no reason to assume they are parallel.
If this is a good, functional description of your part, then this is a good datum scheme. You might want to tighten up the diameter tolerance on your primary datum. Either that, or make sure you understand how your part works at anything other than MMB (MMC?).
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JHG