There are a good few errors and reasons for them missed out there. Everyone understands what the diameter of a circle is. When it comes to the diameter of a pipe end there are many different ways to measure it for many different reasons. You have major problems when a client specifies a criteria and system of measurement without knowing why or the ramifications then doubles down on "the client is always right" when the people making their product try to give them advice. I spent far more of my life than I like to admit discussing ways to measure the diameter of a pipe end.
Do Americans use metric system?
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swampyankee
Chief Master Sergeant
- 4,020
- Jun 25, 2013
It wasn't. Grissom, Chafee, and White didn't make it off the pad.
wuzak
Captain
You are arguing from a theoretical point of view, not a practical point of view.
I've never seen a decimal point without a digit following it. But maybe that's just the engineering world where clarity is required.
if I draw something that is to be 3450mm then I expect it to be 3450mm +/- 0.5mm. The person making that thing will use a measuring device that has markings at 1mm increments, or better.
When I check the thing I would do the same. If the measurement falls between two lines, I determine whether it is closer to the upper of lower measurement. That is, if it is between 3450 and 3451 I don't estimate it to be 3450.3. If it is closer to 3450 it is OK and approved. If it is 3451 it will sometimes be OK, but other times it will be unacceptable - it depends what the thing is for and what, if anything, it fits to.
If the person who built the thing is like you and worked to 3 significant figures and the measurement is not an acceptable measurement, it will be rejected and sent back to be fixed or remade.
mikewint
Captain
I cannot speak to the practicalities of the manufacturing or engineering end of things. Perhaps because in the sciences so many different types/kinds of instruments measuring so many different parameters were in use that it became incumbent that the experimenter state in specific terms the degree of uncertainty in each and every measurement. The sole problem is ZERO because of its dual usage both as a simple place-holder and in some cases an actual measurement digit.
We also used a BAR written over the last significant zero so 93,000,Ō00 miles would indicate that the three zeros after the 3 were actually measured and are therefore significant digits. The fourth zero (with the bar over it) is an estimated digit and therefore an uncertain digit though still significant. The last two zeros are placeholders and not significant.
It was also necessary to not have uncertainty wander all over the place so, for example, you made certain to use the same instrument all the time. So one would always use the same balance to measure mass so that its uncertainty was constant and in the same direction rather than one balance that read high followed by using a different one that read low.
The difference between us is that you were making something that had a practical direct use. If I'm measuring the speed of light through quartz then I don't have a fixed standard to compare my results against. All I can do is make several measurements and compare their precision. I can't find accuracy unless I have an accepted standard. So I measure to my instruments limits, perhaps 4 significant figures. A better instrumentality may later measure to 5 significant figures or better. As the significant figures increase and reading begin to cluster we can get an accepted value to a stated degree of error.
So the new Kibble Balances give us a Planck's Constant of: 6.62607015 × 10-34 kg⋅m2/s Many years ago I consistently used a value of 6.6262 for common calculations. Today that would be in error
We also used a BAR written over the last significant zero so 93,000,Ō00 miles would indicate that the three zeros after the 3 were actually measured and are therefore significant digits. The fourth zero (with the bar over it) is an estimated digit and therefore an uncertain digit though still significant. The last two zeros are placeholders and not significant.
It was also necessary to not have uncertainty wander all over the place so, for example, you made certain to use the same instrument all the time. So one would always use the same balance to measure mass so that its uncertainty was constant and in the same direction rather than one balance that read high followed by using a different one that read low.
That's because you have that 0.5mm tolerance to play with. Your part is acceptable as long as the actual length falls between 3449.5 and 3450.5. So you might not actually write down the estimated .3 but you are cognizant of it none the less. And if that part is 3450.9 it has exceed tolerance and will need to be shaved down a bit.
The difference between us is that you were making something that had a practical direct use. If I'm measuring the speed of light through quartz then I don't have a fixed standard to compare my results against. All I can do is make several measurements and compare their precision. I can't find accuracy unless I have an accepted standard. So I measure to my instruments limits, perhaps 4 significant figures. A better instrumentality may later measure to 5 significant figures or better. As the significant figures increase and reading begin to cluster we can get an accepted value to a stated degree of error.
So the new Kibble Balances give us a Planck's Constant of: 6.62607015 × 10-34 kg⋅m2/s Many years ago I consistently used a value of 6.6262 for common calculations. Today that would be in error
fubar57
General
mikewint
Captain
I'll see your eye roll and raise you a tongue:
fubar57
General
At least we know you can copy/paste a Gif as well
michael rauls
Tech Sergeant
- 1,679
- Jul 15, 2016
I used to run a CNC lathe many, many years ago( one of the many jobs I tried out but didn't particularly care for).
I used to just measure the parts the way they told me with the calipers they gave me. If the parts were within tolerance they went into the good bucket if not into the reject bin they'd go and id adjust the X or Y axis as needed and try again until good.
Seemed like a fairly simple job at the time.
Never realized making parts could get so complicated.
I used to just measure the parts the way they told me with the calipers they gave me. If the parts were within tolerance they went into the good bucket if not into the reject bin they'd go and id adjust the X or Y axis as needed and try again until good.
Seemed like a fairly simple job at the time.
Never realized making parts could get so complicated.
You would not believe the hours I have spent in rooms full of engineers discussing go-no go gauges (which is what I presume those calipers were). Also drifts, tapes calipers, lasers and all things used to measure pipe ends. I frequently noted that about a quarter of the people there didn't know what they were measuring and or why. It actually is complicated. What you were doing is quality control, adjusting x and y axis before you had to put stuff in the reject bin is quality assurance.I used to run a CNC lathe many, many years ago( one of the many jobs I tried out but didn't particularly care for).
I used to just measure the parts the way they told me with the calipers they gave me. If the parts were within tolerance they went into the good bucket if not into the reject bin they'd go and id adjust the X or Y axis as needed and try again until good.
Seemed like a fairly simple job at the time.
Never realized making parts could get so complicated.
mikewint
Captain
I was told many years ago that the reason some cars ran forever and never had a significant mechanical problem while others were lemons from day one was due to the way in which part tolerances came together randomly in the assembly process. By chance a car would come along where all over tolerances were matched with all under tolerances. Or the reverse where everything was at the limit of too big or too small.
When we rebuilt an engine we'd buy 40 pistons, for example, and weigh and mic each and every one until we had a set of eight that were identical. The rest were returned. The same with valves, push rods, piston rods, rockers. etc. The running engine had just about zero vibration
When we rebuilt an engine we'd buy 40 pistons, for example, and weigh and mic each and every one until we had a set of eight that were identical. The rest were returned. The same with valves, push rods, piston rods, rockers. etc. The running engine had just about zero vibration
michael rauls
Tech Sergeant
- 1,679
- Jul 15, 2016
Yes, I was just running parts and making minor adjustments to the program as needed to keep them within tolerance.
This was back when I was about 19 or 20 and had just tacken some machining in general and Cnc in particular at the local junior college. It never did occur to me just how much might have gone into getting it to that point.
That is a difference the Japanese (and others) made in production engineering, narrowing down the variance in machined tolerances.
I've been circle track racing for 30 years, built many engines myself, and been in on building a bunch more.
The approach of sending back more parts than you buy would make you a unwanted customer/client with any parts suppliers I've dealt with, and would quickly get you blackballed with any other supplier. These guys do talk to each other you know.
The way me and my friends balance a engine is balance a set of rods, small and big ends, by machining the pads on the ends intended for that, until we get the rods as close to equal as possible, then do the same with the pistons.
Then put the lightest rod with the heaviest piston, etc until we assemble the engine, if there's any difference left, it's corrected by balancing the crank dynamically.
Big NASCAR race shops do buy pistons, etc. in big bunches, and try to sort them out by equal weights as close as possible. Then use the same approach we do.
They only return defective parts.
In 1988 I bought in the same day from the same car dealer two absolutely identical Fiat Uno
one for me and one for my Wife, as they were very handy to use in the crowded and narrow streets of my City.
After three years my Wife told me "..bring my car to the garage, the crank for lifting the driver's glass is broken…"
Exactly three days after the crank of my Uno car broke also.
Has anybody heard of " programmated obsolescence"?
one for me and one for my Wife, as they were very handy to use in the crowded and narrow streets of my City.
After three years my Wife told me "..bring my car to the garage, the crank for lifting the driver's glass is broken…"
Exactly three days after the crank of my Uno car broke also.
Has anybody heard of " programmated obsolescence"?
It is caused by the genetically engineered crank weevil that takes three years to munch through a crank.
michael rauls
Tech Sergeant
- 1,679
- Jul 15, 2016
I think there's alot of truth that with some bad luck you can get a hold of a car that just by chance ended up with a whole lotta parts that are at the edge of tolerance( and maybe a few that are over) and therefore a real lemon.
I've never heard anything but good things about Subarus so we bought one. Mistake.
We got it brand new and within a few months it had engine troubles, brakes trouble, transmission trouble, and died occasionally when pulling up to a light.
Took it back to the dealer a couple times and even they couldn't fix it. We just traded it in on a Toyota truck a couple weeks ago.
No, I think it was one of the early effects of the Climate Change. The crank wasn't designed for such hot temperatures.
mikewint
Captain
Well its been close to 60 years so I can 'fess up'. In Chicago one of the biggest auto parts retailers was Warshawsky or J C Whitney. One of my best friends was a Parts Manager. Everything I bought was through him. Generally all parts were graded as Good - Better - Best. So I'd call him and order Good and he'd put Best in the box. So while I took home 30 of their Best pistons I was only charged for the 8 I kept the rest went back on Monday and were never charged.
Had another friend in a tire retailer shop. I'd order the smallest cheapest and he'd bring out the biggest and best tires they had in the store.
Was the only way I could afford that beast
The Spanish Air Force flew both T-6's and SNJ's. They kept mph in the T-6's and knots in the SNJ's. I wonder if they kept a single type in a particular squadron but I don't know. The training school used T-6G's so they would have been consistent in mph.
