Question for You Machinist Types

[CalgaryPT]

Is there a recognized symbol for nominal measurement? I know in European countries they use "e" as "Estimated," but that is not the same as nominal measurement. I recently was building something from a blueprint that used the traditional way of noting it by just printing "(nominal)" in parentheses afterwards. But it got me thinking whether or not there in a symbol to denote this....

Perhaps there is something in the Machinery's Handbook?

 

[Brent H]

From what I gather, if you do not specifically identify decimal places and/or tolerances then the measurement is taken as the nominal dimension. For example 9/16 would be nominal as would 3 mm but 0.5625” or 3.00 mm would be specific, as would something with a tolerance or surface finish specification.

 

[Tom Kitta]

Nominal size == a dimension used to describe the general size usually expressed in common fractions.
Basic size == the theoretical size used as a starting point for the application of tolerances.
Actual size == the measured size of the finished part after machining.

Nominal does not seem to be used a lot.

The abbreviation is NOM from https://en.wikipedia.org/wiki/Engineering_drawing_abbreviations_and_symbols

Unless nominal means basic size. Looks like engineers love some confusion.

 

[CalgaryPT]

...

Unless nominal means basic size. Looks like engineers love some confusion.

Agreed.

I saw the NOM abbreviation as well, but could not find the symbol. It is only bugging me because I seem to recall seeing it as a stylized "N" with a horizontal line through it (as in a strikethough in HTML). But I may be wrong. The European symbol for Estimated "e" has a UNICODE representation (U+212E), but there is nothing for nominal.

Oh well. I'll file it in the same part of my brain that wonders why Polysporin has only two antibiotics, One-A-Day Gummies tell you to take two per day, and a myriad of other stuff that would make me Unfriend myself on social media if that were even possible.

Clearly Covid can't end soon enough.

 

[CalgaryPT]

And just in case anyone is wondering how this came up, it has to do with sheet metal. Copper was specified as 22 gauge (nominal), which is to say 22 gauge as if it were steel I discovered.

Gauge isn't standard in sheet metal: 22 gauge copper is 0.028", 22 gauge brass is 0.02535" and 22 gauge mild steel is 0.0299". The standard metal gauge measuring device with all those incremental slots on them is calibrated to mild steel unless otherwise specified. So you can't use them accurately on other metals.

 

[DavidR8]

I didn’t know that about sheet metal. Thanks Pete.

 

[YYCHM]

I didn’t know that about sheet metal. Thanks Pete.

Neither did I. That's kind of insane eh. Who invented the gauge system of measurement for sheet metal?

 

[Brent H]

@CalgaryPT : that is good knowledge to point out. hopefully someone designing things would be on the ball to check into the "nominal thickness" prior to spec'ing the plans/drawings etc.

I was reading an article on "nominal dimensioned lumber" causing all kinds of issues for builders. It did not mention the ages of the builders but I am assuming they are part of the "needs to be perfect" generation that want things to the n'th decimal place. I can grasp some of it but what are you going to call your "nominal 2x4"? in metric its a 38.1 x 88.9.... maybe a "nominal 38 / 88" and so the craziness would continue.....

 

[CalgaryPT]

Neither did I. That's kind of insane eh. Who invented the gauge system of measurement for sheet metal?

It was invented in Britain. Lots of theories where "gauge" number comes from. The most popular is that it originated from wire gauge, and the gauge number represented the number of times it was drawn through a mandrel die to get to the specified size. That's why the larger the number, the smaller the thickness.

 

[francist]

Any of the copper sheet we’ve used for the past 30-plus years is always specified in ounce weight. As in, 16oz full hard, 24oz half hard, etc. Lead as well although the unit is pounds — 4 pound, 6 pound, etc. Brass we always specified by the decimal dimension — 0.032” or “oh-three-two dead soft” , “oh-four-nine half hard”, etc.

 

[YYCHM]

It was invented in Britain. Lots of theories where "gauge" number comes from. The most popular is that it originated from wire gauge, and the gauge number represented the number of times it was drawn through a mandrel to get to the specified size. That's why the larger the number, the smaller the thickness.

And then there is "12-gauge" meaning you can make 12 lead balls, each of equal diameter to the gun barrel, out of 1 pound of lead.

 

[CalgaryPT]

@CalgaryPT : that is good knowledge to point out. hopefully someone designing things would be on the ball to check into the "nominal thickness" prior to spec'ing the plans/drawings etc.

I was reading an article on "nominal dimensioned lumber" causing all kinds of issues for builders. It did not mention the ages of the builders but I am assuming they are part of the "needs to be perfect" generation that want things to the n'th decimal place. I can grasp some of it but what are you going to call your "nominal 2x4"? in metric its a 38.1 x 88.9.... maybe a "nominal 38 / 88" and so the craziness would continue.....

My favourite quote of all time was something I saw on a gravestone: "Perfection is an insult to the Gods." I love that. Even if you aren't religious, that's a keeper.

One of my most humble learnings in life comes from metal fabrication. I learned instead of striving for perfection, to assume imperfection and to design in anticipation of it. This means oval slots that allow for adjustment (instead of bolt holes), levelers for tables, expansion joints in longer projects, to overcut into the waste zone and adjust later on the disc sander, and using jigs and aids like Clecos prior to setting rivets. Extended to the business world I suppose it means always have a backup plan.

Sucks that you have to get older for this to sink in.

 

[PeterT]

The way I understood it & mostly substantiated below - Gauge number has its origins in how many passes the material went though the rollers/dies. So 10 gauge = 10 passes, 15 gauges = 15 passes/ More passes = material thickness reduction. Explains why there is not a linear reduction relative to 1 even step gauge 'unit'. And why different materials have different thickness/gauge size vs say steel based on their ductility. And why wire gauge is different again. (half way down this link) https://www.machinemfg.com/sheet-metal-gauge-sizes-chart-inch-mm/

Personally my brain feels better with good old thickness because it works across a wide range. But unless you are the inventor of the unit you don't get to vote. We Imperialists have a good feel for Horsepower even though these days we don't have much to do with horses or what they can power... unless we watched a YouTube video. In metric lands they predominantly use PS (Pferdestarke or 'horse strength'). Which is metric horsepower = 0.98632 mechanical HP, equivalent to lifting 75kg mass one metre vertically in one second. We prefer lifting 550 foot-pounds per second thank you very much. I just feel bad for the horse LoL.

 

[CalgaryPT]

The way I understood it & mostly substantiated below - Gauge number has its origins in how many passes the material went though the rollers/dies. So 10 gauge = 10 passes, 15 gauges = 15 passes/ More passes = material thickness reduction. Explains why there is not a linear reduction relative to 1 even step gauge 'unit'. And why different materials have different thickness/gauge size vs say steel based on their ductility. And why wire gauge is different again. (half way down this link) https://www.machinemfg.com/sheet-metal-gauge-sizes-chart-inch-mm/

Personally my brain feels better with good old thickness because it works across a wide range. But unless you are the inventor of the unit you don't get to vote. We Imperialists have a good feel for Horsepower even though these days we don't have much to do with horses or what they can power... unless we watched a YouTube video. In metric lands they predominantly use PS (Pferdestarke or 'horse strength'). Which is metric horsepower = 0.98632 mechanical HP, equivalent to lifting 75kg mass one metre vertically in one second. We prefer lifting 550 foot-pounds per second thank you very much. I just feel bad for the horse LoL.

Agreed. Especially when one considers how liberally they rate HP based on some proprietary measurement systems. No way a Red Lion Pump that draws 6.5 Amps @110VAC is 3/4 HP.

That's an insult to 3 legged horses.

 

[DPittman]

And just in case anyone is wondering how this came up, it has to do with sheet metal. Copper was specified as 22 gauge (nominal), which is to say 22 gauge as if it were steel I discovered.

Gauge isn't standard in sheet metal: 22 gauge copper is 0.028", 22 gauge brass is 0.02535" and 22 gauge mild steel is 0.0299". The standard metal gauge measuring device with all those incremental slots on them is calibrated to mild steel unless otherwise specified. So you can't use them accurately on other metals.

Yes the metal gauge thing has made me scratch my head also. Gauges and calibers in the gun world are also inconsistent and confusing.