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Compostie Positional Tolerance on Different Size Holes

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BrianRoach

BrianRoach

Automotive
Jul 8, 2008
10
Hi All,
I have a situation where I have 5 holes of different sizes on a plate. I am currently holding their position using independent positional tolerance callouts on each hole (e.g. hole #1 is specified as diam. 5 +/- 0.5 with a GDT feature control frame specifing a true pos. of 0.1 back to datums A, B & C; hole #2 is specified as diam. 6 +/- 0.2 with a its own GDT feature control frame specifing a true pos. of 0.1 back to datums A, B & C... etc, through all the 5 holes on the plate). This works OK, but I really want to treat all of these 5 differently sized holes as a pattern, and then tighten their tolerances to each other (i.e. have a single feature control frame that applies to all of the holes with a true pos. of 0.1 back to datums A, B & C in the PLTZF and a true position of 0.05 in the FRTZF). If the holes are of the same size it is easy to do this just indicating that all of the holes are in a common pattern by pointing to only one of the holes and then indicating the pattern with a "5X" in front of the specification for the hole. My question is this:
Is their a way of indicating that all these different size holes are in the same pattern so that I can tighten the tolerance on the holes within the pattern?
 
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Brian:
Fig. 5-53 in AMSE 14.5M-94 on page 149 of the standard is exactly what your situation.

Yes, you can have a composite positional feature control frame for the 5 holes that are of different sizes by placing FIVE COAXIAL HOLES below the feature control frame. Each hole size and tolerance must be shown though.

Dave D.
 
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dingy2

I dont believe these holes are coaxial, they are on a plate.
 
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ringster:

Thanks - sometimes I should read the question a bit more carefully.

This is a bit different and there is no example that I can find in the standard but here is what I would do. I would mark each of the 5 holes with a letter - maybe A. Below the composite feature control frame, I would state "FIVE HOLE PATTERN HOLES MARKED A. That would cover it.

Dave D.
 
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Expanding on what Dave just posted; if you want to maintain the existing different individual tolerance zones for each different FOS rather than having them all to a common PLTZF value, then you could leave the individual controls as they are now, PLUS, mark each of them "K" or such. First, they are already a pattern by the principal of simultaneous requirements. Now, put a position callout with a leader to one of the holes with a note underneath indicating "HOLES MARKED K"; this is the FRTZ segment. It's not shown this way anywhere in the standard, but is legal and I've seen it numerous times.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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Thanks for the input guys. I was king of thinking along the same lines. However I don't generally like to add text notes like "HOLES MARKED K" if I don't have to. One of the benefits of GD&T is the ability to use clearly defined symbology to replace what is not always clearly written text. But I think in this case this is the only way to handle the problem. I was hoping I had overlooked some already defined way of doing this that is already documented in Y14.5. Its too bad their is no way to specify a pattern that consists of features of different size and/or shape per Y14.5. Maybe this is something that can be addressed by the committee in future editions of the standard
 
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You don't have to use identifiers "K" or english language "HOLES MARKED K"... just use multiple leader lines pointing from the composite position callout to each of the size callouts.

In automotive transmission valve bodies there are bores with mutiple land sizes... some repeated multiple times and there are often many of these type of bores. To describe one of them with three different sizes in the bore and three lands for each size we typically specify 3X size1, 3X size2, and 3X size3 then point to those size callouts from a common composite position control 9X PLTZF [pos|dia0.X|A|B|C] FRTZF [pos|dia0.X(M)].

By using composite controls for these valve bores our coaxiality refinements for functional fit (FRTZF) are free of simultaneous requirements relative to other valve bore sections... while the general locating controls (PRTZF) that are subject to simultaneous requirements insure good relative location for automated assembly and good stacked location relative to the casting.

Paul

Paul
 
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I'd say use which ever is clearer for your particular drawing. Somtimes multiple leader lines end up making the drawing very difficult to read.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
 
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