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How do you handle people who belittle GD&T and point to their success without it?

How do you handle people who belittle GD&T and point to their success without it?

How do you handle people who belittle GD&T and point to their success without it?

(OP)
My boss today discredited my use of the fixed fastener formula of Y14.5. Since he had never heard of it (he's an EE) and probably because I'm a new guy at the company, he essentially discredited my use of the formula and said "we've made hundreds of thousands of parts here over the years I've been here and we've never experienced fit problems between our PCBs and their housings."

I tried to tell him that any process change, tooling change, or supplier change can cause holes to drift away from their true positions. If they do, and the parts still pass inspection, then the parts are still accepted because the formula guarantees that the parts will fit together as long as all the holes come in within their allowable size and positional tolerances. He summarily dismissed the entire subject before I had a chance to show him how the shape of the tolerance zone alone provides a 57% bigger area for the hole centers to land. He stated that GD&T should only be used for fit-critical situations because the symbols drive up the cost of the parts.

How can you talk sense into someone with this lack of knowledge and appreciation for GD&T?

Tunalover

RE: How do you handle people who belittle GD&T and point to their success without it?

You can't.

I've posted about this before, especially back in my early days.

thread1103-193705: Drawing standards only for Military work was the closest I found with a quick look.

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RE: How do you handle people who belittle GD&T and point to their success without it?

About the best one might do, and it will take a lot of work, is to gather position variation data and do a statistical analysis to see if the current processes might result in a problem. If there isn't a problem and there isn't one predicted, then there isn't much need to avoid it.

RE: How do you handle people who belittle GD&T and point to their success without it?

Quote:

the symbols drive up the cost of the parts

He's not wrong about that, >in the context of his mechanically unsophisticated world<, i.e. if he is equally dismissive of his mechanical part suppliers as he is of you.

DO NOT try to educate him any further; he already knows everything, because he is an EE, and you are not.
There is a current discussion around here on that very subject, but I'll just reiterate that arguing with that boss is a career decision. ... that I have made too many times, and it never turned out well for me.

Find something else to do, and try to steer the company away from jobs/products where tolerance problems can not be solved with a hammer.

... or get a better job while you still have one to leave voluntarily.

Mike Halloran
Pembroke Pines, FL, USA

RE: How do you handle people who belittle GD&T and point to their success without it?

Quote (tunalover)

How do you handle people who belittle GD&T and point to their success without it?

Try to learn from them. Analyse. Follow 3Dave's advise and study the process. Maybe your numbers, that are fine by the "formula", are laughable from the shop's point of view. That will not add you any credibility.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: How do you handle people who belittle GD&T and point to their success without it?

What? You don't just reference a Surface Profile in general notes?

"ALL SURFACES ARE APPLICABLE TO A PROFILE TOLERANCE OF .060" WITH RESPECT TO DATUM A (PRIMARY),DATUM B (SECONDARY), DATUM C (TERTIARY)."

Sarcasm

"Art without engineering is dreaming; Engineering without art is calculating."

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RE: How do you handle people who belittle GD&T and point to their success without it?

tunalover,

Several thoughts here...

Are your parts being machined? Machining is an accurate process, which makes it forgiving of bad drafting. You may be able to do the math and show him that parts meeting the specified tolerances cannot be guaranteed to assemble. EEs are supposed to be impressed with math.

On my machined parts, I tend to apply all-around profile tolerances of 0.4 or 0.8mm. I don't know how the shops cost these. I figure that calling up a 0.8mm profile on a machined part shows that I don't give a s**t. Something else almost certainly is way more important.

I am writing up notes here on DFMA. I am convinced that drafting is a major cost issue. If the shop cannot make sense of your drawings, they will anticipate time on the phone asking you questions, and they will anticipate doing free re-work. They will charge more. There was a good discussion here a while ago on thread1103-322065: Critical Dimensions, on how to tell the shop which dimensions matter.

--
JHG

RE: How do you handle people who belittle GD&T and point to their success without it?

You can emphasize that he isn't wrong, and that your suggestions are not replacements, but improvements. They aren't in competition with existing processes, but simply another, leaner, more efficient way of doing things. It, in no way, seeks to invalidate decades/centuries or performance; that'd be ludicrous.

MikeHalloran, on the other hand, is not wrong when he supports GD&T being a cost INCREASER in many industries or types of fabrication. It is. It simply is. There are simply many shops that work with nothing but calipers, tape measures, and even micrometers who will not give a crap about your true position.
The moderately educated ones will convert the T.P. to a +/- dimension so they can measure it in two directions with old fashioned tools and call it good, raising the price for the additional 'overhead work' of conversions.
The less moderately educated ones will ignore the symbol altogether, raise the price to cover any rejects due to their ignorance.
Then there are the ones who will ignore your print, make the part to "their tolerances" and say "this is all we promise to hold, regardless of what the print says" and you're now behind schedule, over budget, and lack good parts.

That's my experience with the "cheap shops". Both where I've worked, and whom I've used as subs :(

The shops who understand and grok the GD&T language will be shops that are likely already a bit pricier because they hire more-than-minimum wage laborers, have a reputation of quality, probably work to certain standards, and so forth.


I'm sorry- my post is absolutely one of the "sitting on the fence" positions. There's truth to the fact that the world indeed still spinned and parts were still successfully designed before the standardized use of tolerancing specified in Y14.5. You can indeed work to the 'old fashioned' way of doing it and get the parts you need. It's up to you on whether or not you this manager must change his ways, can change his ways, or if you can do it your way without him agreeing. There's no good answer. Pick your battles and decide if this is a hill you truly want to die on.

RE: How do you handle people who belittle GD&T and point to their success without it?

I would never put GD&T on a PCB or other EE-heavy thing because most of the industry just doesn't work that way.

RE: How do you handle people who belittle GD&T and point to their success without it?

Other thing to consider with PCB mounting is that the screws will 'chew' through the board a few thou pretty easily so slight mis-alignments aren't as obvious as they may be with some components.

Where it can be an issue is if it manages to chew thorough the coppper on a hole or something but in most cases I'm not sure this would cause a function problem.

Then there is the issue that simple application of calculations in B4 are 'worst case' not statistical so values may be a conservative.

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RE: How do you handle people who belittle GD&T and point to their success without it?

KENAT,

Yet another thing to consider is that PCBs are CNC machined, especially the holes. The specified tolerances may be inadequate, but the process cannot exploit the sloppiness. Until such time as PCBs are sand cast or welded, there is no problem.

--
JHG

RE: How do you handle people who belittle GD&T and point to their success without it?

Dangit, drawoh. Now I'm gonna have to dream up a welded PCB just for the heck of it.

RE: How do you handle people who belittle GD&T and point to their success without it?

Sure I've been told the holes on pcb's will hit +-.003 day in day out on size & position pretty much regardless.

I don't bother applying GD&T to pcbs - in fact the electrical guys do all the definition I don't touch the drawings.

I just make sure they put a hole big enough to accommodate the tolerance build up from their process and on the mating part. I then GD & T the holes on the mating part converting the +- to pos equivalent etc.

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RE: How do you handle people who belittle GD&T and point to their success without it?

I love the last part of this thread's title: "their success without it."
Yeah, there have been a lot of people or companies that got by for a while without using updated techniques, but eventually it caught up with them.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: How do you handle people who belittle GD&T and point to their success without it?

Quote (KENAT)

Other thing to consider with PCB mounting is that the screws will 'chew' through the board a few thou pretty easily so slight mis-alignments aren't as obvious as they may be with some components.

Where it can be an issue is if it manages to chew thorough the coppper on a hole or something but in most cases I'm not sure this would cause a function problem.

This can create a problem, if the PCB is a multi-layer design that uses one or more screws to force ground plane contact with the housing.

I had a problem once (at the prototype level, so we caught it) where a hole was out of position, causing the screw to bind. The screws in the assembly were very small, so a small deviation in installation torque caused by the screw thread grinding through the edge of the hole was enough to prevent the screw from seating, so the PCB had intermittent ground plane contact at this location. Took the EE guys a period of tail-chasing over an intermittent noise problem to figure out it was mechanical and kick it back to us.

Turned out to be a problem with the prototype casting tool- the PCB was produced via CNC and was right on print.

RE: How do you handle people who belittle GD&T and point to their success without it?

The other problem with screws chewing copper off a PCB is that the copper ends up somewhere, eventually.

Mike Halloran
Pembroke Pines, FL, USA

RE: How do you handle people who belittle GD&T and point to their success without it?

But if he doesn't understand GD&T, how much longer will he be viable in the job market?
He's just been lucky so far. The next time he sends out his resume, others who have equal skills but also GD&T will get the job.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: How do you handle people who belittle GD&T and point to their success without it?

I have worked for tunalover's manager, or equal, too many times.

Mike Halloran
Pembroke Pines, FL, USA

RE: How do you handle people who belittle GD&T and point to their success without it?

All of the PCB layout guys I have ever worked with seem to "eyeball" placement of holes, components, and board edges. It is only when I complain that "these mounting holes should be in-line with the others" will they be fixed.

"Art without engineering is dreaming; Engineering without art is calculating."

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RE: How do you handle people who belittle GD&T and point to their success without it?

I guess that's true, Kenat.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: How do you handle people who belittle GD&T and point to their success without it?

I would agree with KENAT's assertion that low or no GD&T knowledge won't affect an EE's job prospects. In a past life I spent a fair amount of time in meetings with EE staff who were oh-so-proud of their new PCB layout, asking questions like "What tolerances do you expect on this hole, or this edge?" and getting blank stares in return.

In my opinion, someone who thinks GD&T adds cost either doesn't understand what GD&T does, or is not evaluating things in a big enough frame of reference.

My typical solidworks model of a part takes maybe 8 or 10 hours. Creating a drawing (or set of drawings) for that part takes another 2 or 3 lets say. If I take that basic drawing and add GD&T features where appropriate, it might add another hour or so versus using basic (as in simple, not GD&T BASIC) dimensioning.

So sure, GD&T adds $100 to the cost of the drawing.

Then the guy at the machine shop gets it. If he's competent it maybe takes him a little longer, let's say another hour, to interpret the drawing and quote accordingly. He builds that extra time into his quote- so if it's one part, you add another $100 or whatever.

The real point is that you've now added $200 to part cost- but if you've done your job, everyone now understands what the part needs to do. You've spent $200 so that you don't have to spend $50,000 on part rework after the production line is running, or parts are at the customer, or whatever terrible scenario could arise that gives us nightmares.

I think, regardless of what type of engineering we practice, everyone on this board has at some point worked for a boss or program manager or customer who did not understand why we do things a certain way. My approach in these situations has always been to approach things from the financial side- PMs and bosses care about profit and margin more than anything else- and used correctly, GD&T is a tool which can increase both. If you frame it that way, he will get it.

RE: How do you handle people who belittle GD&T and point to their success without it?

(OP)
Now guys although my new boss is an EE, somebody put him in charge of a group of purely mechanical MCAD designers and MEs who deal with GD&T almost daily in their design of die cast and injection molded parts (I'm fairly new but so far it doesn't looks like any of the designers understand the method; they just give the MEs what they ask for).

After my meeting with him, it dawned on me that he doesn't care to learn anything about something his guys spend a lot of time with. The truth is he will rely on perception rather than facts when it comes to an issue involving GD&T and go with the guy who has the most convincing speech or the guy that he once decided is the one that is usually right, not the guy who puts the facts on the table.

Management is chock full of people who believe that if they don't understand something then it's not worth knowing hence it has no value. The boss I had before this one never strung the three words "I don't know" together. Ever know someone like that?

In any event, I have carried the GD&T torch faithfully for many years and will continue doing so. You know IPC promotes GD&T and requires that all dimensioning and tolerancing conform to ASME Y14.5-2009 on PCB drawings. But it is still true that the standard is entitled "Dimensioning and Tolerancing" not "Geometric Dimensioning and Tolerancing" so the ECAD designers and fabricators fall back on bilateral (±) tolerancing which is approved even though it is vague and subject to interpretation. I have yet to meet an EE or ECAD designer that understands or uses the method or had any interest in learning even the bare essentials.

Tunalover

RE: How do you handle people who belittle GD&T and point to their success without it?

I worked in engineering for 29 years and have been an educator at a community college for 16 years teaching the Y14.5 standard. Many of my faculty colleagues think the standard is an overkill and adds cost by tightening tolerances and making product verification more difficult.
I am ASME Senior Technologist for the Y14.5 standard. I frequently conduct training at companies. Last Spring I worked for five companies.
The motivation for the training and potential change is driven internally (frequent problems)or external (customer demands - similar to the ISO 9000 registration need).
Typical domestic business model - if it ain't broke, don't fix it.

John

RE: How do you handle people who belittle GD&T and point to their success without it?

I don't think anyone can deny GD&T is not very intuitive, unlike the concept of +- dimensioning which anyone can understand. I have never been in a precision manufacturing environment but I have never seen GD&T used except for a flatness callout here and there

RE: How do you handle people who belittle GD&T and point to their success without it?

Hi Tunalover,

Could you explain a little more how a bilateral tolerance is "vague and subject to interpretation."

thanks

Dan T

RE: How do you handle people who belittle GD&T and point to their success without it?

I agree with Tmoose.
Please explain how a bilateral tolerance is vague and subject to interpretation. I often hear very lengthy discussions in the product design group on how to apply and interpret GD&T. This does not seem to happen when using +/- tolerances.

L. Jones

RE: How do you handle people who belittle GD&T and point to their success without it?

Tmoose,

--
JHG

RE: How do you handle people who belittle GD&T and point to their success without it?

Yes, the standard is ASME Y14.5-2009. :(

--
JHG

RE: How do you handle people who belittle GD&T and point to their success without it?

I don't see the problem with inspecting that exaggerated depiction. The 'implied 90' rule and youe stated angular tolerance covers form and location (2.1.1.3), and size/location is covered by the linear dimensions. Trying to split hairs beyond that is making mountains out of molehills.

RE: How do you handle people who belittle GD&T and point to their success without it?

JNieman,

We have had this discussion. thread1103-261904: Plus Minus Tolerances

Do you measure to the holes from the nearest edge?

How do you take into account the angle error of the bottom edge, or is it the side edge?

--
JHG

RE: How do you handle people who belittle GD&T and point to their success without it?

I understand the complications.

I also recognize that despite the arguments and near-chicken-littling, people have been making and using parts like that successfully since.. the industrial revolution, I suppose.

I guarantee that to this day, gobs and gobs of structural base plates are made from drawings just like yours, or made from drawings with nothing but tail/ordinate dimensions from some point.

The descriptive language defined in Y14.5-xxxx is awesome and clarifies many things, leaving fewer issues open to interpretation. I simply refuse the supposition that it is the -only- way to get things done successfully.

Whether using 'legacy' dimensions or ASME Y14.5 form/size/location controls from basic dimensions, designers must account for the most likely result of their drawings. Risk assessment comes into play. A necessity for knowing how the parts will be made is very helpful.

Yes, one way is inherently less risky than the other. I simply refuse to think the 'sky is falling' (hyperbolic, I know) because people still make drawings using plus/minus dimensions. I think it's too easy to forget that there are entire worlds of manufacturing outside of some of the niches we work in. I've worked in many different types of manufacturing and engineering environments which I'm grateful for. Mostly I've gone to the more-precision-oriented end of the spectrum from start-to-present.

RE: How do you handle people who belittle GD&T and point to their success without it?

JNeiman,

Eventually parts will be simply made with smaller levels of variation than drawings are likely to call for, eliminating the need for specifying tolerances.

Conventional hole clearances were chosen based on the most likely hole location errors, but since their adoption precision of location has significantly improved.

Many companies put off full part inspection in favor of 'key' characteristics and expecting to catch and fix errors on the factory floor, a strategy that works as long as those variations remain small.

I fully expect concerns about dimensioning and tolerance analysis to disappear in the same way that people no longer care about the C scale or the D scale on slide rules. Calculators carry unneeded precision, but the calculations are so cheap it doesn't matter.

RE: How do you handle people who belittle GD&T and point to their success without it?

I too have apparently worked for tuna's boss and several variations of him that had particularly odd/wrong/other ways of doing things. Personally I just tend to go with it and do the work in the requested fashion, sooner or later it either blows up on the supervisor or I head elsewhere. Just my opinion, but given that GD&T's been in pretty common use for ~30 years now its rather embarrassing for anyone in industry unable to use it whether they be an EE making board/harness/enclosure/other critical prints or a supplier running parts and definitely career limiting.

RE: How do you handle people who belittle GD&T and point to their success without it?

3DDave,

I keep claiming that machining drawings are easy due to the accuracy of the process.

Let's design an investment casting, and let's do some DFMA, and ditch the subsequent machining. The bolt holes must be cast in place. Casting tolerances are around .005"/in last time I checked. Probably, I want to use a larger bolt than I would have on a machined assembly, simply because they cannot cast a small hole in place. I need to do quite a bit of analysis to work out the positional tolerance, the tolerance of the hole diameter, and the size of the hole that will make the process reliable.

How accurate is 3D printing? How accurate is a urethane mold made from a rapid prototype?

--
JHG

RE: How do you handle people who belittle GD&T and point to their success without it?

Quote (3DDave)

I fully expect concerns about dimensioning and tolerance analysis to disappear in the same way that people no longer care about the C scale or the D scale on slide rules. Calculators carry unneeded precision, but the calculations are so cheap it doesn't matter.

Ha Ha Ha Ha Ha. You crack me up. You obviously don't work in a high precision, high production rate industry. Take a look at a modern 8 to 10 speed automatic transmission or thousands of other complex mechanisms and tell me tolerance analysis is going to disappear any time soon.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: How do you handle people who belittle GD&T and point to their success without it?

Ha Ha Ha Ha Ha. You crack me up, thinking that I was referring to every possible application*.

The transmission example, much like that which I've done for multi-stage gear reductions that included temperature variations with milliradian accuracy requirements, isn't all that complex. At most it is tedious. Complex ones include deformation due to loads, temperature offsets, and transient temperatures.

*On other occasions I've mentioned the importance of understanding how floating point calculations are made, but for most people it isn't important. These calculations are done on a lot more complicated machines than any automobile transmission will ever be. Even the cheapest calculator requires manufacturing precision far beyond what goes into a drive train.

RE: How do you handle people who belittle GD&T and point to their success without it?

Quote (3DDave)

Even the cheapest calculator requires manufacturing precision far beyond what goes into a drive train.

Have you ever designed a modern powertrain system, including controls?

Complex ones include deformation due to loads, temperature offsets, and transient temperatures.

RE: How do you handle people who belittle GD&T and point to their success without it?

Apparently I know what is required.

RE: How do you handle people who belittle GD&T and point to their success without it?

Quote (3DDave)

Even the cheapest calculator requires manufacturing precision far beyond what goes into a drive train.

Really ??? ponder, do you actually believe that statement? I'll have some of whatever your smoking pipe

RE: How do you handle people who belittle GD&T and point to their success without it?

ICs are now pushing 15nm. That means alignments for these chips on the 1-2 nanometer level. What are you smoking?

RE: How do you handle people who belittle GD&T and point to their success without it?

IC paths are fabricated at 15nm, sure- that doesn't mean the chips on a board in a $3 calculator are aligned to single-nanometer levels.

You're also not likely to find 14nm chips in 'the cheapest calculator'.

RE: How do you handle people who belittle GD&T and point to their success without it?

Very little machining going on in microchips. The lithography machines required to make state of the art chips are huge investments that only a handful of companies in the world can afford. The fact that such things can be fabricated at all has no bearing on dimensioning and tolerance analysis for the rest of the world.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: How do you handle people who belittle GD&T and point to their success without it?

Quote (dgallup)

The fact that such things can be fabricated at all has no bearing on dimensioning and tolerance analysis for the rest of the world.
Neither does the specialized development of high end, mass produced automobile transmissions, which only a few companies in the world do. I think the number of companies designing transmissions is about the same order of magnitude as those designing IC manufacturing machines and far smaller in number than those designing ICs.

Interesting the hostility to the idea that (generalizing) Manufacturing, which makes those transmissions, won't continue to be improved to an extent that most mechanical components will be made more precisely than their operating variation limits require, eliminating the need to specify those limits. Except, it seems inevitably, for 8 speed automatic transmissions, which will forever require a couple of experts to tell everyone else that it never will.

RE: How do you handle people who belittle GD&T and point to their success without it?

Many products continuously push the current state of the art manufacturing capabilities, ensuring the continued need for concerns about dimensioning and tolerance analysis. Look at the aspheric lens in your cell phone, the DI fuel injectors in your car, the artificial valves about to be implanted in your heart. Your example of micro chip manufacturing requires great concerns about dimensioning and tolerance analysis to achieve acceptable production yields. The fact that a cheap chip can do 64 bit floating point calculations only makes it easier to carry out dimensioning and tolerance analysis, in no way does it eliminate the need for it. We have had a new CNC machine sitting at the supplier for 6 months because they have yet to meet the run off Cpk requirements. I see a long long future for improved production processes and concerns about dimensioning and tolerance analysis.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: How do you handle people who belittle GD&T and point to their success without it?

As processes improve tolerances improve. As tolerances improve, products improve. As products improve, design tolerances tighten. As design tolerances tighten, processes are pushed to their limits. As processes approach their limits, they must improve and the cycle starts over.

This will never end.

RE: How do you handle people who belittle GD&T and point to their success without it?

(OP)
Oh I forgot to mention another reason why my boss thinks that all their hole positions have been trouble-free:

In most companies, the pass/fail inspection rate is typically kept by the QA Engineer who steps in any time parts are rejected because they are out-of-spec. He normally calls or emails the supplier directly to figure out what the problem is and see that a solution is implemented and providing the expected outcome to the buyer. Many parts are rejected and returned for a refund by the supplier without Engineering ever knowing about it. but that number is not shared with the design engineers if it's not deemed a design problem. So the engineering manager (my boss) never knows about it when parts are thrown out for not meeting the print. Of course by virtue of the shape of the bilateral tolerance zone being a square and the GD&T tolerance zone being circular, the GD&T tolerance zone will be 57% greater in area (putting aside additional tolerance if the hole departs from MMC).

Hell, multitudes of functioning parts have been tossed out in the past because their centerlines did not fit in the box-shaped tolerance zones from bilateral tolerancing. Common sense says that dimensional variances happen radially from the center and that, as long as the hole axis falls within a certain radius of the true center then the part will fit. With the bilateral method, if the tolerance is, say, ±x in both directions and the part comes in with a hole at coordinate (x,x) then the part just passes. If it comes in at (x,-x),
(-x,x), or (-x,-x) then the part also marginally passes inspection. Those coordinates are the corners of the square tolerance zone. The distance from the hole center in each case is x√2. But what if a hole came in at (0,x√2)? This is the same distance from the center but is outside the box. The part is thrown out. But we know the part will fit if the hole center falls in a circle of radius x√2 about the true position!

I think these concepts are too large for my boss to follow so I think I'll just have to give up trying to convince him he is wrong.

Tunalover

RE: How do you handle people who belittle GD&T and point to their success without it?

Quote (tunalover)

...

Of course by virtue of the shape of the bilateral tolerance zone being a square and the GD&T tolerance zone being circular, the GD&T tolerance zone will be 57% greater in area (putting aside additional tolerance if the hole departs from MMC).

I don't generally push that advantage of true position tolerances. Only if your process is marginally capable of meeting requirements, does true position tolerance reduce your scrap rate. If my process were marginally capable of locating holes, I would enlarge the holes.

The thing I like about true position is that it applies the tolerance directly to the hole. This is as opposed to applying it to a line that passes through several holes, not all the same size, and not all the same tolerance requirement.

--
JHG

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