Pos Tol applied to pattern (how to?) 6

[fcsuper]

I have a X,Y grid pattern of holes laid out flat plate. Datum A is on the facing surface. Datum B runs through the part in the X direction. Datum C runs through the center of the part in the Y direction. (See the attached drawing.)

I wish to apply positional tolerance to the holes of the pattern.

What's needed, what's basic, what's reference?

Matt Lorono
CAD Engineer/ECN Analyst
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Lorono's SolidWorks Resources
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[PaulJackson]

No Kenat this is what I meant...

 

[KENAT]

I thought that's maybe what you were talking about, as it's more or less what you showed in your previous sketch, but I'm not sure it matches fcsupers situation.

If his part can be redesigned to accomodate your scheme great. Howevever, if he's stuck with 2 separate sets of alignment features, dependant on orientation as per my sketch, which I've got a feeling he is then what?

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[PaulJackson]

Then he's stuck with more variation period! What is quality all about??? Reducing variation!

 

[fcsuper]

Well, I can't redesign the part or the fixture. However, I don't see why I can't employ this Paul's dimensional scheme (which I believe I did in my last example...anyone care to confirm just so I can get a sanity check?...I'm pretty burnt out on this right now).

I think I can justify using the 2x pattern because both directions need to be symmetric, and this forces symmetry. So even though both pin holes are not engaged in the fixture, both can be engaged individually to provide common results, as long as I control the adjacent slots well enough.


Matt Lorono
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Co-moderator of Solidworks Yahoo! Group
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[fcsuper]

here's the updated image to my previous posting:

Matt Lorono
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[ringster]

To the extent of the drawing, as depicted,the scheme by Paul should work. In fact, I happen to know of one of the panels on the space station by Boeing which was dimensioned in a very similar manner.

 

[KENAT]

Matt, I came to about the same conclusion after Pauls last post. The basic idea looks about as good as any suggested to my mind. In fact, is this a case where hole slot is better than hole-hole? The pattern is tied to to two holes. Whichever orientation you're in you are using one of the holes so are related locationally pretty well. So long as you get adequate clocking from your slots it seems like a good solution.

Only thing I'm a bit unsure on is given your 64 hole pattern now reference A and D, is there a clocking/orientation issue as the D planes are at an angle to the outline. Should an angle be given for the pattern to the plane between the 2 D hole axis?

I think you'd get what you need but I'm not totally sure it's bullet proof.

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[fcsuper]

"Only thing I'm a bit unsure on is given your 64 hole pattern now reference A and D, is there a clocking/orientation issue as the D planes are at an angle to the outline. Should an angle be given for the pattern to the plane between the 2 D hole axis?"

Since the distances between the holes are basic and orthogonal to the part, the specification is complete. However, I did talk to my contact at an inspection house about this scheme and he did ask that I add the angle as a reference.

Matt Lorono
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Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
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[KENAT]

Sounds good to me, print it;-)

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[btrueblood]

"Only thing I'm a bit unsure on is given your 64 hole pattern now reference A and D, is there a clocking/orientation issue as the D planes are at an angle to the outline. "

I don't think that is the issue, the pattern is drawn and dimensioned perpendicularly to the datum hole "pattern" if you will. But, the location of the two datum holes "D" are not completely defined relative to the pattern...I think...the dimensioning scheme Matt is showing works, because the centerline implies the "D" holes are located halfway between two columns of the pattern. But long ago I got beaten about the head and shoulders rather severely in this forum about implied datums and implied symmetry. My shampoo bottle still hasn't recovered...

'Twere me, I would dimension the x-y location of the datum "D" holes from the center(s) of one of the pattern holes, using basic dimensions (looks like two each [0.500] dimensions would suffice). The extra basic dimensions may arguably be redundant, but redundant basic dimensions are allowed and even encouraged elsewhere in ASME Y14.5M (remember the circular bolt pattern arguement discussion awhile back...

 

[KENAT]

btrue, the 2 holes that are used to create the D datum are generated from the width/height of the part, datums B&C. Then the 64x pattern from D. Simplistically the 2 holes come first then the pattern, it sounds like you're saying it's the other way round?

As to the implied center, I vaguely recal that incident. Generally there is no such thing. However, in certain situations i.e. when using datum feature center planes it seems it's allowed. I couldn't find the text that backs it up in 14.5 but figure 5-4 shows it (yeah I know 1.1.4 is inplace;-))

However, I wonder if the horse needs me to keep beating it.

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[fcsuper]

Unless I'm misunderstanding this conversation, centers I'm using are explicit to my understanding of the standard, since the standard says when such exists (even if it is not directly noted on the drawing). However, on the real drawing, I did add ref dims linking the center datums to the patterns just to make the point clear.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
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[looslib]

I do have one comment, and is not really related to the this thread directly.
You have Datum A as the top of the part. When I was taught GD&T, from a Y14.5 committee member, we were taught to think of the datums as the inspection setup planes.
To inspect your part, the inspector would plase the countersunk hole side down on the inspection device, then work from there.
Do I have that right or am I missing something?


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[ringster]

Looslib,

I would say yes.

Is the committee member still a member and still teaching?
.

 

[KENAT]

Shouldn't the primary datum be decided first by function and then by inspection concerns?



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[fcsuper]

Looslib,

I cannot discuss design intent to that degree.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[btrueblood]

"btrue, the 2 holes that are used to create the D datum are generated from the width/height of the part, datums B&C. Then the 64x pattern from D. Simplistically the 2 holes come first then the pattern, it sounds like you're saying it's the other way round?"

Yes, I'm saying you do it the other way around. Fcsuper has said, repeatedly, that the outer profile is less important. If that's so, then the D-datum holes would be held to tight tolerances relative to the pattern, and loosely to the outer boundary. If I was inspecting the part, I'd look at the tightest tolerances, and start my inspection there. If I read the drawing, and was making the part, I would grab any old sheet that had enough room, punch/drill/laser/waterjet the hole pattern, and then indicate off the hole pattern to lay out and shear/cut/trim the edges of the plate.

In reality there is not any preferred "order" to the datums, you can design, fabricate, and inspect, in any order you please, as long as you satisfy the requirements...

 

[KENAT]

btrue - I proposed similar making the 64X pattern the datum earlier, based on what fcsuper said about the edges not being that important. Then the problem of exactly how that's interpreted in practice became an issue, and not one that I think was ever fully resolved above.

I then restrained myself to looking at the scheme fcsuper came up with hence the request for clarification on what you were saying.

I do agree that people sometimes get too caught up in following the datums during manufacture etc. The important thing is to meet the final intent - that doesn't always mean manufacturing in the order of datum precidence etc.

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[btrueblood]

Kenat, I think we are saying the same thing.

My reply "Yes, I'm saying you do it the other way around. "

I now retract. I shoulda said, 'you do it in whatever order you want, but meet the requirements nonetheless.'