Slot pattern Datums 2

[nmine]

I have had this question for sometime and have only seen instances where there is a hole as datum b and plane of a slot as C. What if you have a flat plate with two slots and you want to control the outer edges of the plate using a profile tolerance with respect to the slots (slots are centered). How would you use the slots as a secondary/tertiary datum to control the outer edges of the plate to the slots?

 

[Garland23]

Attached is an example of a slot-type shape being used as a datum feature, from Fig. 7-3 of the ASME Y14.5 standard. However, since you are asking about two slots, you'd have to be careful not to overconstrain the degrees of freedom. Perhaps you could reference B and C with the "M" modifier (MMB).

Others will chime in, but you can use this graphic as a starting point for what you're trying to do.

 

[jassco]

Your datum feature A controls 3 DOFs (degree of freedoms). You can use width of 2 slots together as secondary that controls 4th and 5th DOFs which is rotation and translation up and down. You will need one more feature to control 6th DOF so that you plate does not move side to side horizontally. To do that, you can either use one of radius or center plane between the two slots.

 

[nmine]

@Garland23 Thanks for the reply! So this is Constrained DOF for Primary Datum Features. If the flat surface of the plate was datum A then you applied datum feature symbol B to a slot, this would just then constrain the remaining DOFs not over constrain right? Similar to if you had B and C as the sides of the plate? If this is correct, if you apply a datum feature symbol to a composite profile tolerance that controlled both slots would this then imply center plane of slots and axis centered between slots?

 

[nmine]

@jassco would the datum feature symbol just be added inline with the basic dimension dimensioning slot centers?

 

[3DDave]

Using 2 or more slots as a single feature will not overconstrain the datum feature.

The datum feature symbol is applied to the FEATURE surface, not the location dimension, just as shown in the clipped figure.

The result is a framework that has no defined origin; the standard sucks in failing to make this clear for patterns or groups of features used as a single datum feature.

 

[mfgenggear]

I have had this question for sometime and have only seen instances where there is a hole as datum b and plane of a slot as C. What if you have a flat plate with two slots and you want to control the outer edges of the plate using a profile tolerance with respect to the slots (slots are centered). How would you use the slots as a secondary/tertiary datum to control the outer edges of the plate to the slots?

View attachment 7988

Generally slotted holes are ti allow slight adjustment of a component. If I am correct.
I would go an other way. I would pick large face as Datum C, the left hand end Datum A, and and edge as Datum B, 3 degrees of restrained.
While inspecting a pusher clamp on the end ti restrained.
I would true position with MMC in FCF tolerance.
With basic dimensions to Datums A and B
If the objective is to hold the slots in line a composite FCF true position. With no datums.
Thus ensuring alignment at a tighter tolerance if necessary.

 

[jassco]

@Op:

Bottom face is the primary feature for datum A.

Your secondary datum feature B can be attached to dimension of 2x width of the slot.

Your tertiary datum feature C can be attached to distance between ends (inner or outer) of the slots.

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