×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

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

Please have a look at my application of GD & T

Please have a look at my application of GD & T

(OP)
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

RE: Please have a look at my application of GD & T

2
1) If you are working in inches and using the ASME standard then you should remove the leading zeros (section 1.6.2 a).

2) Your surface profile FCF is from S to T but you also have the "all around symbol". This is a conflict.

3) Your tapped holes may benefit from using a projected tolerance zone (with bonus tolerance, mmc) or from positioning the minor diameter of the threads. As it currently stands your are putting the position requirement on the axis derived from the pitch cylinder (section 2.9) with no bonus tolerance. Some would say this will be difficult to measure.

4) You have multiple patterns of features (holes) on this part. You may benefit from using compound position or multiple single segment position for these features (see chapter 7).

RE: Please have a look at my application of GD & T

sammcc,

Based on a quick one-minute examination, the GD&T symbols appear to be applied correctly.

From a functional standpoint, there may be issues. The cross holes in Section X-X are located tightly relative to A|B|C. But I would think that you need them positioned tightly relative to the 10.50 mm holes, and the position of these holes is not toleranced.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Please have a look at my application of GD & T

All features under GDT control have same datum sequence A|B|C, so Simultaneous Requirement is in effect - they are all one pattern of "holes"

M12 holes are not shown in ISO view. Is this 3rd of 1st angle projection?

Part has symmetrical features. This will add confusion as to which feature is which datum. Might want to label datums on the part.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

This is unrelated to actual application of GDnT (sorry) the but I know of no better way to ask - OP or anyone else, what the font is that is utilized for this drawing? I find it extremely pleasing to the eye and readable.

Apologies for the off topic question.

RE: Please have a look at my application of GD & T

Hello all, I just wanted to piggyback off this post. I was never taught GD&T in school and now I'm working on some drawings that will be submitted to a big deal auto manufacturer. I'm trying to wrap my head around it and I think I'm getting the idea bit by bit. I'd really appreciate if someone who knows what they're doing could take a look at this and give me a little guidance. I know I need to take a class or something to hammer it down.

This part has an angled surface with a ~6mm hole centered on it that a part goes into and then some M3 set screws hold the part in place. I can post a picture of the real part if that makes it easier to understand.

Thank you!

RE: Please have a look at my application of GD & T

Immediately noticed a mistake on the right view. I meant to reference C and D in the frame, not A and D

RE: Please have a look at my application of GD & T

Your projected view doesn't look right. The hole should appear oval in that view. This make it unclear the vector that the 25.4 is from datum feature C. You need one more datum reference to completely constrain all the degrees of freedom. A|D|C| would do it.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

RE: Please have a look at my application of GD & T

Thank you! I really wasn't sure if I should make it an oval or if that would be confusing. Should I do the math and make a literal projection of the round hole at 45deg? I only have access to 2D.

I understand that referencing D|C| would constrain the hole's position with reference to those planes, but what exactly does referencing A do? Does that specify "yes, this hole is on surface A," thereby constraining it in the DOF perpendicular to the page?

RE: Please have a look at my application of GD & T

You need the diameter symbol in front of the geometric tolerances in both position FCFs.

Incorrect call out of Datum Feature A in the right view. The arrowhead should be a dot.

RE: Please have a look at my application of GD & T

Let's start a new thread so we don't completely hijack this one.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

RE: Please have a look at my application of GD & T

Okay, I'll start a new thread.

RE: Please have a look at my application of GD & T

sammcc,

The view in zone D7 does not appear to be a proper projection from any other view on the drawing. I'd suggest eliminating it after transferring the note and dimensions to the view in zone B4 (which I'll call the front view).

It appears you're relying on the laser engraving to eliminate ambiguity as to which surfaces are datum features A and C, so you might want to add a back view to make it more obvious that the engraving is only on one surface.

Presumably there's a general note somewhere that assigns a tolerance to the non-basic dimensions where tolerances are not shown. I doubt the same tolerance is appropriate for all these dimensions, especially the ones related to the laser engraving.

The specification that defines the M12 X 1.5 thread should have a tolerance for the minor diameter, so I'd suggest removing the 10.50mm diameter dimension. If you actually want to override the standard tolerance, that should probably be done as part of the thread callout.

What does "BS3642Pt. 2" refer to? BS 3642:1963 - Specification for aluminium baking dishes (other than dishes based on the 530 mm x 325 mm basic module) seems unlikely to be relevant.

pylfrm

RE: Please have a look at my application of GD & T

(OP)
Hi All,
Many thanks for your responses.
I think I should have explained what this part actually does and what the critical features on it are.
So its a block, the real critical features are the 2x dia .201/.197 holes in section x-x. Two photodetectors are fitted into these and their alignment to each other is pretty critical.
The M6 holes in this view are for a plastic grub screw to block off the hole left by drilling the holes mentioned previously.
The M12 holes are for a cable glad to fit into and the 10.5mm hole x 2.3 deep is for a piece of 2 core cable to go into this is soldered onto the photodetectors before they are fitted.
The .205/.197 holes in the top centre view are mounting holes so their position is not overly critical either.

AndrewTT:
I have incorporated your points 1 & 2- basic mistakes on my part.
Sorry I should have explained the function of my part- Do you think your points 3 & 4 are required based on this.

AXYM:
I have added centre lines and changed the note to 2x tapping drill .
Because they are only for a cable to go through the position relative to the cross holes is not overly critical.
Sorry I should have explained the function of my part up front

mkcski:
Projection is 3rd angle. The reason the M12 holes arent in the ISO view is because they are on the bottom face.
I agree reference the problem establishing which face is the datum. How do I get around this? Do you mean physically engrave the datum on the part or change the design in such a way that it is not symmetrical?

chez311:
This is the standard font in NX. I believe it is unique to it.

pylfrm:
-I have added a note to the view in D7 stating that it is an auxillary view to show the position of the laser engraving only. This part is anodised and is laser engraved after this.
-With regards to the ambiguity of the datum surfaces- I see this is a problem but I can't rely on the laser engraving to indentify these, this problem was also addressed by mkcski. Do you have any ideas how I get around this- make the part non symmetric or marking the surface to denote them
-There is a general note in the drawing border to cover non basic dimensions
-I have removed the 10.50mm dimension and replaced it with the words tapping drill

-BS3642 should have been BS3643- sloppy mistake on my part.
I have removed the specification and changed the call out as to how Y14.5 calls threads out.

Latest version of the drawing attached- thanks guys, I appreciate everyone taking the time to help me out here.

RE: Please have a look at my application of GD & T

sammcc:

Regarding the symmetrical issue...we used semi-permanent marker in our plant to identify datums. But we mfg VERY large parts (20ft dia +), so the customer does source inspection in our plant. If your customers or other down stream users are doing mfg or inspection that would require the identification of datums you might want to consider: vibro-tool, acid etching, steel stamps or a non-functional feature to "defeat" the symmetry.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

(OP)
The thing with this part is that it is in full view when in use and aesthetics are important so a non functional deature is probably best to ensure consistency. I guess I could add a rad or chamfer onto one of the top internal corners of the "u" shape profile, this would remove the symmetry.

RE: Please have a look at my application of GD & T

If you want the holes for the photo detectors to be coaxial to a tight tolerance your current method is fine. However, if the location of these holes does not need to be precise, as long as they are coaxial, then you could use compound position or multiple single segment position to achieve this. This could lower the manufacturing cost while not affecting function.

If the two .205/.197 holes (still have leading zeros...wink) are for mounting then you should be looking at the floating faster formula or fixed faster formula (appendix B), as appropriate, to select the required position tolerance. Also, you may need to use compound position to refine the orientation error of these holes for proper function.

How do you measure the position of threaded holes at your work?

RE: Please have a look at my application of GD & T

(OP)
Hi Andrew & all,

For manually measuring threads we in the case of these would use a pin with the same diameter as the minor diameter of the thread and check the position that way or if not manually then CMM

I have updated the drawing as follows:
-Removed the last of the leading zeros from the drawing!

-added an additional rad on the top of the "u" section. This will remove the symmetry issue and allow the datums to be identified correctly.

-used composite frames to increase the positional tolerance of the mounting holes and photodetector holes while maintaining the coaxiality / orientation requirement




RE: Please have a look at my application of GD & T

That new radius should be described with a basic dimension. Maybe you already did that in the notes section.

I am guessing that you will want the lower segment of the 2X Ø.205/.200 compound position FCF to have datum A called out. This will keep both holes perpendicular to datum A within Ø.002 while also holding the feature-to-feature relationship (.750 - .250 = .500) tightly.

RE: Please have a look at my application of GD & T

sammcc:

I notice you have "DRL" on the cross holes. I would not recommend specifying processing information to define feature characteristics. See Fundamental rules 1.4 (e)

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

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.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

(OP)
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?

RE: Please have a look at my application of GD & T

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

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

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][B], or [A][B][C] in the lower segment. You cannot just put [C], this would have no meaning according to ASME Y14.5-2009.

RE: Please have a look at my application of GD & T

(OP)
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.

RE: Please have a look at my application of GD & T

(OP)
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

RE: Please have a look at my application of GD & T

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.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

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

What am I misunderstanding?

RE: Please have a look at my application of GD & T

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.

RE: Please have a look at my application of GD & T

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)

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

(OP)
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?

RE: Please have a look at my application of GD & T

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.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

(OP)
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.

RE: Please have a look at my application of GD & T

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.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

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.

RE: Please have a look at my application of GD & T

(OP)
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.

RE: Please have a look at my application of GD & T

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).

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

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:

Quote (Y14.5-2009 para 7.5.4.1)

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.

RE: Please have a look at my application of GD & T

Quote (mkcski)

.....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.

RE: Please have a look at my application of GD & T

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

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

mkcski,

Sorry - you seem to just be explaining the rules of simultaneous requirement vs separate requirement, my questions did not have to do with the basic underlying concept... I am very familiar with how patterns behave when referenced as SEP vs SIM REQT, there is no lack of understanding what they mean. Apologies if I did not make this clear.

What I am trying to understand, and what greenimi seems to be reinforcing, is (1) is the verbiage in 7.5.4.1 vs 7.5.4.2 REALLY saying that separate requirements cannot be applied to DRF's with only planar/non-FOS at RMB and (2) if that is so, the concept also seems to be extended to DRF's with FOS referenced at RMB, how can this be seeing as 4-41 seems to do just that?

The extended question would be that if (1) and (2) are both true (my mind almost goes to say they are not, and that it was an inadvertent omission that implies something which was not intended), for what would be the reasoning behind any of this? It seems to be an arbitrary limitation, I can think of plenty of times this would be at the very least inconvenient.

RE: Please have a look at my application of GD & T

chez311: Para 7.5.4.1 does not state that SEP REQT can be used on RMB datums. This conflicts with para 4-19 and fig 4-41 which shows that it can/does. I have always landed on the datum shift concept in 7.5.4.2, but the SEP REQT logic makes functional sense in fig 4-41 with RMB datums. Your opinion?

greenimi: It makes no GD&T sense to me to use SEP REQT on fig 4-2 because not a good example as there is only one pattern of holes. Sorry if I mislead you. But consider fig 7-52 which also has no FOS datums. The basic dims locating the holes in both patterns originate from the same DRF, so there is no logic in allowing them to be separate. I look to "cartoon" hard-gages to clarify my understanding. In this case, separate gages would have the same simulated datums. One would have 6 pins for the lower pattern. The other gage 4 pins. Since there are no FOS datums there is no shift in effect. Given this all 10 pins could be on one gage and accomplish the confirmation of acceptable position. Am I missing something?

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

chez311: may last post was done before I saw you last post. But my "your opinion?" still applies.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

mkcski,

I would say the fact that it is omitted in the verbiage in 7.5.4.1 is not enough to disallow its use - as you say fig 4-41 shows it can be used and makes functional sense with RMB FOS datums, I agree. I do concede that with non-FOS/planar datums that the lack of datum shift may reduce its functionality/usefulness to call out SEP REQT however I can see situations where it might be desired.

1) You reference 7-52 and that it *could* have a gauge which has all 10 features checked simultaneously and would be almost the same instead of two separate gauges. I don't know exactly why, but on a similar part someone could desire these two be checked separately - perhaps if a similar part its not practical to check them in the same setup.

2) For a multiple single segment control like fig 7-46, as shown all the lower segments are held to simultaneous requirements and are a single pattern - since only [A|B] is called out in these lower segments it could be desired to allow them to float in relation to each other (but still within the larger zone dictated by the upper FCF) even though both A and B are planar, non-FOS datum features. SEP REQT could be applied here to facilitate that.

RE: Please have a look at my application of GD & T


chez311,

For sure, functionally is the driving force when selection datums. But one must recognized that the interpretation of the FCF is based on Y14.5, and when "things" are not specifically defined in the Standard, the interpretation can be problematic (which is why we are having this discussion and for most posts on this forum as well).

1) I agree, there are many reasons that the two patterns could be inspected independently.

2) I agree, in fig 7-46 the upper and lower frames are completely independent, so SEP REQT could be used on the lower segment. But why not the upper too.

Thanks for the great discussion. SEP REQT is not one of my strong area. I am stuck on datum shift as the "cause" for SEP REQT. I need to find examples where shift isn't the reason for SEP REQT. I still need to spend more time evaluating SEP REQT where all of the datums in the FCF are NOT FOS.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

mkcski,

Absolutely agree - there are times when we must read between the lines and extrapolate/interpret the standards meanings and that has been the source of many a heated debate here and elsewhere. Here we have an omission which if taken at face value seems extremely arbitrary - in this instance I would look for a driving reason why exactly this restriction would make sense and I just don't see it. On the contrary as we have shown there can be several cases where it would be useful to specify SEP REQT with non-FOS/planar datums (and in fact is also done right in the standard per 4-41) and I don't believe it causes any issues or violations of other rules in the standard. Thank you as well - I was not aware of the specific verbiage/differences in those two sections and I'm glad you brought it to my attention.

Just a note on (2) - for sure the upper segment could be specified with SEP REQT as well, I was just focusing on the lower segment to show an instance where the tolerance zones could be allowed to significantly shift relative to each other/pattern with SEP REQT without being able to take advantage of datum shift and having a DRF with planar/non-FOS datums.

RE: Please have a look at my application of GD & T

chez311: My supervisor just gave me an estimate to work on, so I will have to bow-out of this discussion for the time being. I think we came to a "conclusion". See ya.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

Consider the allowable angle between the surface selected as datum feature C and the surface selected as datum surface A and the variation in the projection from d/f C of the cross-drilled holes relative to the blind holes that are based on d/f B, which also has significant variation relative to d/f A.

Try building a model that has one face that is 0.020 smaller on the sides and 0.020 larger on the base and then build the holes relative to those surfaces, recalling that d/f A will only contact the datum simulator at the highest points.

RE: Please have a look at my application of GD & T

sammcc,
On your latest edit in regards to your datums themselves it looks like nothing was changed, besides removing any form/orientation controls which are critical for datum definition (not sure why you removed those? they are now held to your relatively loose all around .020 profile tolerance except for A which is uncontrolled).

Quote (sammcc)

bearing in mind the outside profile sits in mid air with no functionality at all

Two of your datum features B and C are contained in that profile. Are these (or datum feature A as well) actually functional or mating surfaces, or are they as you say "with no functionality at all"? Datum selection should always be driven from part function first - your three planar features are "nice" surfaces but if they don't reflect how the part functions or assembles then they are arbitrary.

RE: Please have a look at my application of GD & T

mkcski,

I enjoyed the discussion and it came with a nice conclusion which is often rare on these topics, thanks for humoring me.

RE: Please have a look at my application of GD & T

(OP)
Dave & Chez
Datum surfaces B and C are not functional or mating in any way.
Datum surface A is the mating face, it is where this block attaches onto another smaller block.
The contact area is minimal but I do think I will add the flatness tolerance back into datum surface A

RE: Please have a look at my application of GD & T

sammcc, it doesn't matter if they are functional, you should try building the model to see what your callouts currently accept, because you have said to mate d/f B and d/f C with the inspection equipment and possibly are leading the machinist to to do the same when he creates the holes that reference them as a primary datum reference.

RE: Please have a look at my application of GD & T

Quote (3DDave)

it doesn't matter if they are functional

3DDave - you aren't suggesting what you seem to be, are you? Would you disagree that datum selection should be driven primarily by functional intent? In this case I might agree that there may not be many features precise enough (drilled/tapped holes) besides the surfaces selected and therefore might require an alternate set of datum features - however since these are non-functional surfaces OP has changed in his latest revision from a perpendicularity tolerance (and flatness on the primary) of .005 to profile of .020, a 4x increase in tolerance zone size which will directly affect the accuracy of any features held to these surfaces.

Quote (sammcc)

The contact area is minimal but I do think I will add the flatness tolerance back into datum surface A

sammcc - you have a datum feature controlled by the size tolerance on the thickness of the part (1.000) which is held to print tolerances. I don't know what that print tolerance is but it is likely looser than one would typically want for a datum feature. If that is acceptable then I guess I'll see myself out, but I would recommend as 3DDave suggested that you build your model and perform your stacks to ensure the variation is acceptable - from your first revision to your latest there has been a large jump in the allowable tolerances your datum features are held to.

RE: Please have a look at my application of GD & T

sammcc: I hesitate to go here and do NOT recommend it from a mfg and inspection perspective, but I think I need to mention it as alternative way of thinking from a purely design view point. If, as you say, only the holes are functional in the assembly, then the exterior surfaces can be located from the functional holes in the part. This is contradicts traditional thinking where holes are located from the exterior edges of the part. Again I don't not recommend this because, in most cases, it makes inspection problematic. We make parts where the primary requirement is that a pattern of (24) clearance-holes in the part must align with threaded holes in the mating part. So the edges of the part must "follow" the clearance-hole pattern, making the pattern of holes a datum for the edges of the part. We wrestled with the inspection procedure for months.

Certified Sr. GD&T Professional

RE: Please have a look at my application of GD & T

(OP)
So, the general limits on 1.00" dimension is +/-.010

I have drawn a quick sketch to show the functionality of the part.

It is part of a test fixture and is mounted to a base plate via a mounting block so part of face A is the only face that comes into contact with anything.

RE: Please have a look at my application of GD & T

Well Chez, in this case it is part of a series of suggestions for a model building exercise. So that's what I was suggesting.

RE: Please have a look at my application of GD & T

3DDave,

My apologies if I came off wrong, I thought your statement about it not mattering if they are functional was related to mine about datum selection being driven from part function.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

White Paper - Reliability Verification for AI and ML Processors
Artificial intelligence and machine learning are seeing growing adoption in a wide range of applications. ICs used for AI/ML applications are characterized by large parallel processing computation units, high power dissipation, and complex circuitry that can deliver maximum performance within a strict power budget. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close