Relating One Hole pattern to another hole pattern

[bohornback]

I have a GD&T question regarding the use of a pattern of features as a datum to locate another pattern of features.

Two plates (1 and 2) that are at an angle to one another (about 135 deg lets say). One plate has Datums A,B,C (surface, edge, edge). The other plate has D,E,F (surface, edge , edge).

I have one four hole pattern in plate 1 that is the critical pattern (the other pattern is located off this critical pattern). It is .060 positional (MMC), A, B, C (the location of the pattern isn't as critical). With hole to hole of .010. This pattern then becomes Datum G.

My question is, what is the correct way to represent the GD&T so that the pattern in plate 2 is positioned relative to the pattern in plate 1 (now datum G)?

I currently have that this pattern is .030 positional (MMC), D, G, F. Hole to hole of .010. This hole pattern is located with basic dimensions from E, and F (edges of plate 2). Is this valid? Do I have to establish a basic dimension(s) to locate the pattern in plate 2 to the pattern in plate 1?

The end goal is that they are trying to make a tool that can locate both pattern simultaneously, since thier positon relative to each other is critical. Being on plates that are angled from one another, this seems a little difficult.

 

[PetieSmo]

I admit I don't fully understand what your process is. It sounds like there are two options:
1) Locating the plates before the holes are drilled in Plate 2. If that is the case, this should be no big issue to align the plates, and locate the holes relative to the pattern on Plate 1.
2) If the holes in Plate 2 are already drilled and located with respect to D, E, & F, you will need a way of establishing the location of the plate as a function of the holes.

However, process aside, GD&T will allow you to relate your datums (Specifically 'B' & 'E') with an angular (basic) dimension, which should lock down these locations. Another approach is to establish a new datum plane through the centers of two of your holes (perpendicular to A) and defining the second hole pattern off of that.

Hopefully this points you in the right direction. A sketch of your application might help us guide you better with specifics.

PetieSmo

 

[CheckerHater]

I also would appreciate some more info, but the way I see Your setup, you mey get away with smaller number of datums (unless there is something you didn't tell us about).

Your datums A, B, and C create coordinate system and anything else can be dimensioned in relation to that system.

Is my part looking anything like yours?

 

[drawoh]

bohornback

Your term "critical pattern" means nothing to me. What are you trying to accomplish?

If your first pattern is your attaching screws and your parts are located off your specified datum, you need tolerances that ensure your hole clear your screws. Is your second pattern really located from the first, or is it located from your fixing datums?

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JHG