Pipe flange, how to time slotted features

[R1chJC]

Hi All,

Hoping you can help with a question.

I have a part as shown in the attachment. I want to control the rotational orientation of the slots with respect to the holes in the base flange. I'm not sure of the best way to achieve this, can anyone offer some suggestions? The parts mounts via the flange and holes, an additional part is then located in the end via the top slots.

I was thinking something like the shown datum scheme.

Thanks.

 

[Belanger]

Yes, that's pretty much the scheme to use -- but put "2X" before the slots' feature control frame, and probably add "M" after datum B reference in that same feature control frame.

 

[R1chJC]

Thanks Belanger, I'm struggling to get my head around how that datum scheme works however, is there some implied relationship by drawing it that way?

 

[Belanger]

Datum A of course establishes your primary plane. Then datum B -- with the "M" modifier which we call MMB -- means that the two holes together will be plugged into with fixed-size pins. Because they are fixed size, there is the possibility of some wiggle room, which we call datum shift. But with just datums A and B, the part is fully constrained in all six degrees of freedom. If you have access to the ASME Y14.5 standard, check out Figure 4-39 and read the text of paragraph 4.12.3.
I should probably have mentioned that you'll want another position tolerance on the two holes that create datum B, similar to Figure 4-39.

Once you have a fully constrained part, you can locate just about anything using the proper GD&T symbols (in your case, position).

 

[R1chJC]

Thanks again, so something like the attached? Does setting up the hole pattern as a datum in effect give you the shaft axis then? I'll take a look at the ASME again when I'm back in the office.

 

[AndrewTT]

Add a "4X" before the position FCF for the pattern of holes.

The pattern of 4 holes as a datum feature will yield two perpendicular planes that are also mutually perpendicular to datum plane A. The intersection of these two planes can be considered a datum axis. However, it is not the axis of the shaft. The OD of the shaft will also need to be positioned to your datum scheme, as will the OD of the flange. The shaft OD and the flange OD are RFOS (regular features of size). They need to be controlled for size, shape, orientation, and location. Your size limits will give you size and shape control. The position FCF will cover the orientation and location control.