Please have a look at my application of GD & T 7

[sammcc]

Hi all,

I am a novice with regards to the proper application of GD & T.
I have attached a drawing of a simple part I have added it to- where previouly it was dimensioned without it.
Can you give me some feedback with regards to the application of the symbols I have used.
I am working to ASME Y14.5 and in units are inches.

Thanks

 

[mkcski]

sammcc:

I also noticed the datum sequence is the same in all FCF. Did you consider the effects of the Simultaneous Requirements in para 4.19 of Y14.5-2009.

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[sammcc]

Andrew- your right so I have called out datum A. Should I then reference datum C on the M6 holes for the same reason as this is the face on which they are derived?
Also, the 3X R.130 basic dim covers the additional rad in the U shaped profile

mkcski- both your points are taken on board and incorporated.


Guys, thanks for your continued input here. I have learned loads here.

The latest version is attached, any further refinements?

 

[mkcski]

SAMMCC: Unfortunately you cannot disconnect FCF with SEPT REQT when the datums are not Features of Size (F0S). I missed directing you to para 7.5.4.1. page 146 in Y14.5-2009 Sorry

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[AndrewTT]

I am guessing that proper function of the photo detectors does not depend upon their orientation w.r.t. datums A, B, or C. They only need to be pointed at each other. In that case your current compound position FCF is good. If you need the tolerance zone coming from the lower segment to be constrained in rotation to any of your datums, then you have to follow the rules of compound FCFs. This means you can put [A], [A], or [A][C] in the lower segment. You cannot just put [C], this would have no meaning according to ASME Y14.5-2009.

 

[sammcc]

mkcski- I'm finished work for the day I will read 7.5.4.1 tomorrow morning and re-evaluate this.


AndrewTT- Yes I understand, I have re looked at this and I think I understand the rules around this although I might be back with a question to confirm my understanding tomorrow morning.

 

[sammcc]

mkcski- with reference to 1.3.32.1 does that not make the 3 datum faces features of size?
Also, is the sep reqt call out not legal as per 7.5.4.2?

Thanks

 

[mkcski]

SAMMCC: Planar (flat) surfaces are not features of size (FOS). Your datums A, B and C have extent - a boundary - but the surface itself has no edges. Please see para 1.3.32, page 4 in Y14.5 - 2009. I use the caliper test to confirm a FOS; you have be able to check the size with a caliper or micrometer. Like a cylinder, a sphere or a set of parallel planes (width) which have opposing elements.

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[sammcc]

Do the 1.00 , 3.155 & 2.540 dimensions not allow the caliper test to be carried out?

What am I misunderstanding?

 

[AndrewTT]

A set of opposed, parallel surfaces is a regular feature of size. A single surface is not. You are using single surfaces as datum features.

 

[mkcski]

sammcc: These dimensions you refer to are the distance between TWO flat surfaces and thet are FOS. However, you are only using ONE of the two sides as a datum and not both. The datum feature symbol is applied differently if you want to use BOTH sides as a FOS datum, in which case the center-plane between the TWO sides is the datum. Please see figure 4-3 on page 50 of Y14.5-2009. Note the difference between the symbols and the interpretation of rows (a) and (b). Your datums are (a) and not (b)


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[sammcc]

Confused.
I was aiming for location per Fig 4-2
So then, what I need to do to correctly apply this is to move my datum B of the FCF and onto the horizontal line to the left of the 2.540 dimension line.

Does this make my SEP REQT call out legal?

 

[mkcski]

sammcc: The datum reference frame (DRF) established by your datums is the same as that in figure 4-2. So you do not need to change anything. You cannot use SEP REQT with figure 4-2 datums - they are not FOS, so the same applies to your part. With your part, one setup/gage would be used to check all features at the same time because the are all located from the same DRF established by A| B | C

As a side bar.. might I suggest you take a GDT course to get you up to speed with GDT basics including constraining the 6 degrees of freedom of motion. The application/selection of datums is very complex and is driven by function and fit up requirements - so every part is different.


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[sammcc]

i am back from a 4 day GD & T course (TEC-Ease). But as you have just said- application and selection of datums is complex and the only way I will learn is by doing examples. Looking at examples that are already done is one thing but applying it to parts that dont have it is a completely different ball game.

I do not want to limit this part to being set up or checked using one gauge.
i will need to rethink whats happening here.

 

[mkcski]

sammcc: You do not have to use a hard gage. You use a CMM too. And the patterns of holes do not have to be inspected at the same time But why "setup" the part several times to the same datums to check different patterns located from the same DRF.

I am glad you appreciate the datum "dilemma". Learning by example is great. I would suggest you purchase as many books as you can to "find" more examples to study and expand your understanding. This forum is great for answering questions.

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[chez311]

mkcski,

Could you explain why you are saying that SEP REQT cannot be utilized with planar or non-FOS datums? I see nothing in 4.19 that forbids that (the section which introduces SIM/SEP REQT) - is it something to do with the fundamental nature of planar vs FOS datums? I was not aware of this.

 

[sammcc]

mkcski- this forum is a great place for having queastions answered and I dont want to become a pest either, but a great way of learning is by asking people who know.
I am a long time reader of this forum.
Also, we make these parts in small qtys so while coordinate guessing machine is a possibility it is good to be able to measure parts manually if the cmm is backed up or on a runner.

 

[mkcski]

chez311: It has to do with datum shift when FOS datums are specified at MMC of LMC (MMB/LMB)- fixed not variable simulation with RMB. See 4.11.9, page 63 of 2009. When SEP REQT is NOT specified, the shift applies to all pattern together as a group together (hence the term simultaneous). When SEP REQT is specified the shift applies to each pattern independently (hence the term separate).

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[chez311]

mkcski,

So I re-read the section 7.5.4.1 that you referenced earlier, I understand what you mean now. I see that in 7.5.4.1 for SIM REQT w/ RMB it says "they are considered to be a single pattern" (implying SEP REQT is not allowed, as you suggest) in contrast to 7.5.4.2 for SIM REQT w/ MMB where it says "there is an option whether the patterns are to be considered as a single pattern or as having separate requirements". I was not aware of such a rule - what would even be the reasoning for this?

That being said, 7.5.4.1 also utilizes the verbiage:

Where
multiple patterns of features of size are located relative
to common datum features not subject to size tolerances,
or to common datum features of size specified on an
RMB basis

Does this suggest that SEP REQT cannot also be utilized on FOS datum features referenced at RMB as well? This is a startling revelation, if thats the case, how is Fig 4-41 legal? Sorry for the side bar but this is new information to me.

 

[greenimi]

.....You cannot use SEP REQT with figure 4-2 datums - they are not FOS, so the same applies to your part......

I would say that is wrong!!! Not true and not supported by the verbiage and figures in the 2009 standard.

 

[mkcski]

chez311: An example: See fig 7-54 on page 149. Consider it to be a removable coupling between two shafts. Two bolts go into the 6mm holes and engage one shaft. Two larger bolts go in the 10mm hole and engage the other shaft. The two sets of holes do not assemble to the same shaft, so the patterns are independent of each other and are treated a SEP REQT


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