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Restrain a part

slipper57
This is really, sorta, not a CMM question.... but then again, it is. And I have never been disappointed by the knowledge of this forum! ANYWAYS...

I have a drawing, its a sheet metal part, that in the notes says I can restrain to 10 lbs MAX.?? (to datums). How would anyone rate the poundage of a clamp holding down a part, on a CMM table? Kind of a grey area. When we have a machined parts its suppose to be measured in the 'free state' ?? Again... the part will move if you do not clamp them down. Any thoughts?? Its funny because an "engineer" will say.. "thats suppose to be in the free state" , only if their part isn't correct. And I tell them... .show me how YOUR supplier inspects this part without holding it down....nothing ever becomes of this.

Any thoughts would be appreciated!
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  • Where I work, we generally consider the part to be measured in the 'free state' when there are only 3 points of contact. We may apply force directly to those points of contact and still consider it 'free state' because theoretically no force is being used to flex the part. We'll typically use spring clamps, suction cups, double sided tape, or magnets.

    If we apply force someplace other than directly against each of the 3 points of contact, then we will consider it restrained - like placing a part on three standoffs and putting one clamp in the middle of them. If the part is forced to rest against more than 3 points of contact, we will definitely consider is restrained.

    That said, I agree with . It is best to document your methods and clear them with the 'customer'.
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  • Where I work, we generally consider the part to be measured in the 'free state' when there are only 3 points of contact. We may apply force directly to those points of contact and still consider it 'free state' because theoretically no force is being used to flex the part. We'll typically use spring clamps, suction cups, double sided tape, or magnets.

    If we apply force someplace other than directly against each of the 3 points of contact, then we will consider it restrained - like placing a part on three standoffs and putting one clamp in the middle of them. If the part is forced to rest against more than 3 points of contact, we will definitely consider is restrained.

    That said, I agree with . It is best to document your methods and clear them with the 'customer'.
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