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Posted: 1/17/2023 11:38:44 AM EDT
[#1]
Quote HistoryQuoted: Keep watching this thread to see if geometric tolerancing was used for dimensioning the parts in question. As an old hammer and axe machinist and autocad person, I had some classes on geometric tolerancing, but never used it. Thought it was supposed to make parts that pushed the edges of being out of spec still play nice together. Haven't made things in about 20 years, miss the satisfaction of that work. GD&T does give you more tolerance to work with. A quick example would be to think about the position of a hole with (+.005/-.005) for both x and y. Drawing the normal tolerance zone would give you a square. However GD&T takes into account that the position (+.005/+.005) is still good, but actually greater than .005 from the desired location. In reality the actual tolerance zone is a circle with a radius of just over .007. This gives roughly 57% more total tolerance than non-geometric tolerancing allows. It gets a LOT more complicated but this is a very basic view of how it works. |
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Posted: 1/17/2023 11:41:46 AM EDT
[#2]
Quote HistoryQuoted: LoL. You have never worked in aviation They were AS9100D. If you read my post they 100% inspected PW,GE and RR parts. Also, automotive is one of the few industries that has the volume and the pressure to make it right the first time. |
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Posted: 1/17/2023 11:47:35 AM EDT
[#3]
Quote HistoryQuoted: This just happened to me. Parts rejected by FNG inspector, his boss knew he was wrong, let him reject our parts to "teach him a lesson". Let it go all the way through the process, Back charged me, corrective action..the whole deal. I was hot. Mistakes happen we are all human, but to let it happen intentionally and cause all the bullshit downstream... Quote HistoryQuoted: Quoted: When I worked Supplier Quality I used to lean towards, "vendor defender". There was nothing more embarrassing for a QC guy than to have a coworker write a suppler up for making the exact part we asked for.  Let it go all the way through the process, Back charged me, corrective action..the whole deal. I was hot. Mistakes happen we are all human, but to let it happen intentionally and cause all the bullshit downstream... It recently happened to me as well. Parts were perfect but the mating off the shelf bushings were on the low side of their stated tolerance. My customers QC guy did a knee jerk rejection of my parts without checking the Carr-Lane bushings that he assumed were perfect, the bushings were in spec but not perfect which matters when pin to bushing clearance is only 0.0002". That inspector has it out for me, I have proven him wrong several times over the years so he goes out of his way to find something to bitch about. What is funny about that is he jumps at the chance to bitch without anything to back up his argument. Knowing how he is I make sure what I send them is dead nuts in spec. |
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Posted: 1/17/2023 12:13:10 PM EDT
[#4]
Quote HistoryQuoted: It's always cheaper to make it right the first time. Scrap costs money, as does rework. Quote HistoryQuoted: Quoted: LoL. You have never worked in aviation They were AS9100D. If you read my post they 100% inspected PW,GE and RR parts. Also, automotive is one of the few industries that has the volume and the pressure to make it right the first time.  They don’t give a shit when it is built into the cost! Also, some process are not ever going to be capable or it would be prohibitively expensive to try. |
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Posted: 1/17/2023 12:25:17 PM EDT
[#5]
Quote HistoryQuoted: What the bean counters and egg heads need to understand, is when they ask for things like 1.33cpk, they are paying for holding 1/2 the tolerance called for on the print. 
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Posted: 1/17/2023 12:25:50 PM EDT
[#6]
Quote HistoryQuoted: You know standard deviation? Think of that as the width of your car. Your garage is your tolerance range. Cp is how big the garage is compared to your car. Cpk is how big the garage is compared to to the car, AND how close to center you parked it. It's a statistical method that measures how capable your process is, i.e. how likely you are to make a part out of spec. GD&T for Statistics 
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Posted: 1/17/2023 12:30:21 PM EDT
[#7]
All I can add is that I am in complete and overwhelming awe of people like you who can do this stuff. Same kind of thing like when I see a masterpiece art piece by like Michelangelo. To me people like you are in that same world of excellence.
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Posted: 1/17/2023 12:52:06 PM EDT
[#8]
Quote HistoryQuoted: All I can add is that I am in complete and overwhelming awe of people like you who can do this stuff. Same kind of thing like when I see a masterpiece art piece by like Michelangelo. To me people like you are in that same world of excellence. I would add precision welding to that list! Pure art! |
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Posted: 1/17/2023 1:43:01 PM EDT
[#9]
Quote HistoryQuoted: All I can add is that I am in complete and overwhelming awe of people like you who can do this stuff. Same kind of thing like when I see a masterpiece art piece by like Michelangelo. To me people like you are in that same world of excellence. Thanks but I'm not even close. I know how to get a machine to do what I want. Have no hope in hell to paint or draw beyond a 4th grade level.  I stand in awe of 2 and 3D artists. |
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Posted: 1/17/2023 3:29:46 PM EDT
[#10]
Quote HistoryQuoted: Thanks but I'm not even close. I know how to get a machine to do what I want. Have no hope in hell to paint or draw beyond a 4th grade level. I stand in awe of 2 and 3D artists. Quote HistoryQuoted: Thanks but I'm not even close. I know how to get a machine to do what I want. Have no hope in hell to paint or draw beyond a 4th grade level. I stand in awe of 2 and 3D artists. Quoted: I would add precision welding to that list! Pure art! |
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Posted: 1/17/2023 4:41:45 PM EDT
[#11]
I rely heavily on the TLAR(That Looks About Right) system of measurement.
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Posted: 1/17/2023 11:31:20 PM EDT
[#12]
Quote HistoryQuoted: They don’t give a shit when it is built into the cost! Also, some process are not ever going to be capable or it would be prohibitively expensive to try. Quote HistoryQuoted: Quoted: Quoted: LoL. You have never worked in aviation They were AS9100D. If you read my post they 100% inspected PW,GE and RR parts. Also, automotive is one of the few industries that has the volume and the pressure to make it right the first time. They don’t give a shit when it is built into the cost! Also, some process are not ever going to be capable or it would be prohibitively expensive to try. I remember having an argument at work where someone wanted a certain tolerance on a PA66 part. I pulled out my DuPont design guide for Zytel, because they invented PA66... So, the guide has tolerance recommendations for "normal" and "tight", I don't recall how they label them but someone wanted to exceed the tight tolerances on an automotive part... It wasn't my part so I was ignored. I and DuPont were proven correct in the end though. |
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Posted: 1/18/2023 12:32:01 AM EDT
[#13]
Quote HistoryQuoted: They don't. They know there is a high likelihood they will get good parts from me. He was asking the likelihood of "any shop" being able to hit 1.33 cpk in production. Quote HistoryQuoted: Quoted: This should only apply to production parts. Are you a machine shop or production facility. Capability calculations can only be meaningful if the process is already in a state of statistical control. The parts have to be measured in run order not randomly. Why do they care what your process capabilities are? They don't. They know there is a high likelihood they will get good parts from me. He was asking the likelihood of "any shop" being able to hit 1.33 cpk in production. There are way to many variables. Three big ones off the top of my head. 1. How good were your spindles made orginally? 2. How old are your spindles? 3. What are you measuring with? |
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Posted: 1/18/2023 12:44:53 AM EDT
[#14]
OP, I have no idea what this is about, but it sounds like you have a good relationship with the customer. Is there a way you could say, "English, motherfucker. Do you speak it?" But in a nice way, of course.
The reason I ask is because I was in a very technical field during my career. It would have been very easy to confuse everyone with technical jargon, and impress them with my brilliance. Instead, I always made a big effort to explain everything in language the client could understand. I was complimented many times on my clarity and ability to communicate effectively. |
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Posted: 1/18/2023 8:51:02 AM EDT
[#15]
Quote HistoryQuoted: OP, I have no idea what this is about, but it sounds like you have a good relationship with the customer. Is there a way you could say, "English, motherfucker. Do you speak it?" But in a nice way, of course. The reason I ask is because I was in a very technical field during my career. It would have been very easy to confuse everyone with technical jargon, and impress them with my brilliance. Instead, I always made a big effort to explain everything in language the client could understand. I was complimented many times on my clarity and ability to communicate effectively. I've always made extra effort to communicate well, too. It's very important on many levels. I've tried to impress on the kids how important it is, as well. Many times, they've been shown strings of emails demonstrating various aspects of the subject, good and bad examples. Had a good discussion with this guy yesterday so we're both on the same page . He's a devout Christian , so I'm not sure he'd get the SLJ reference. But, yeah, we broke it down to real English and what such a requirement is, in effect, asking. I appreciate the discussion here. Combined with my own research and discussion with a couple other SME, I have a good handle on this aspect of manufacturing, at least enough to intelligently discuss it with customers. |
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