Please critique my first GD&T drawing 1

[KT12345]

Hey,

Long time lurker, first time poster. I'm looking to update some of my older drawings to be compliant with Y14.5-2009. To my knowledge, I'm the only person at my company with knowledge of the GD&T symbols and system (recently certified as a Technologist), so I don't have anyone to run this past--I was hoping I could have a draft checked. This is a generic base plate for an Instron universal tester. The only critical feature is the bolt pattern, 4X M6 X 1 on a 125 X 50 rectangle. I don't know the position tolerance of the tapped holes, so I started with a 6.4 clearance hole and my own position tolerance of 0.4 at MMC. I have opted to make the pattern its own datum, from which future holes/slots can be located relative to the DRF the pattern creates. We usually make the base plates from 6061 stock, so flatness is already controlled to a point we are satisfied; the the outer dimensions, and spacing of the pattern to the edges, are less critical.

Thoughts? In hindsight, my position tolerance for the holes may be off (it's double the fixed fastener tol equation), but I'm curious what feedback I receive.

Thank you in advance!

Kevin

 

[greenimi]

May I know which 3 DOFs were constrained?

I agree with jassco. 3 was a typo on my part. Should have said 4. Too hastily. Sorry about that.

I think Greenimi meant a hole mathematically controls 4 DOFs (x, y, u and v) instead of 3. But it depends on length of the holes. If it is a short hole, it will only control 2 DOFs (x and y).

Agreed.

 

[3DDave]

Of the four degrees possible to control with a hole, there is always a practical limitation on the two rotations - they just vary in degree based on the engaged length. They never go away. One limiting geometric factor is only reached when the part is infinite thickness, at which point the stiffness of the mating part is zero so that there is no orientation control. The other is a constant for length zero based solely on the size of the hole. In between are a variety of interactions.

 

[SeasonLee]

By the way, I do not agree with this statement.

Would you please advise for what reasons you do not agree with this statement?

There is only one primary datum A referenced, so only 3 DOFs(Z,u,v) are constrained, X and Y direction still free to move.

Season

 

[greenimi]

SeasonLee,
One of the holes in this pattern of features could stop 4 DOF (2 rotations and 2 translations), but together these holes can stop 5 DOF (one additional rotation)

 

[SeasonLee]

During this stage, only one primary datum A being referenced, the hole pattern datum B not included in the DRF yet, so I still think stop 3 DOFs only, if the DRF being constructed with |A|BM|, I will agree what you said. Interesting! I will stand corrected if I am wrong here.

Season