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wbleeker
04-01-2007, 03:48 AM
When you get a set of plans for something and all the dimensions are in fractions it is nothing but a PITA, Micrometers and Verniers and Digital Verniers read in DECIMALS and always have, And the blokes that draw the drawings have to use these to make the item, so why the BLOODY HELL don't they put the DECIMALS in the drawing.Putting the dimensions in decimals would save those of us who are not constantly doing this from working it out.
It is logical that the drawing should be dimensioned this way and I can't see any reason why not, unless of course the dimensions are quoted as rule size which to me is half a millimetre or 20 thou.
Even on those measurements that are not critical it would be easier if the drawings were dimensioned in decimals.
Will

John Stevenson
04-01-2007, 06:00 AM
I fully agree with you Will.
Not wanting to start a imperial / metric war again but if all dimension on ENGINEERING drawings were done in decimal then it would go a long way.
The problem is with Imperial there are two dimensions for every size.
Take 37 /64"
To most non anally retentive people this is a meaningless number, is larger than 32/64" which is 1/2" and that's about it.
Taken to a decimal it becomes more usable at 0.578" To most of us who can remember the large way marks like 0.500 for 1/2", 0.625 for 5/8" and often the intermediate ones like 0.5625 for 9/16" this decimal then becomes more usable.

So our indecipherable 37/64" becomes 0.578" which is a tad over 9/16" and many can even do the simple mental arithmetic to get 16 thou bigger.

.

speedy
04-01-2007, 08:01 AM
Hey Will, would those plans be from the good old USA by any chance?:)
For those who may not know how to convert. Get out the old calculater and divide the numerator by the denominator, no probs. But you knew that already mate.

Swarf&Sparks
04-01-2007, 08:29 AM
Just to muddy the waters further, why not dimension everything in HPGLU?
40 to the mm, 1016 to the inch. :D

JCHannum
04-01-2007, 08:29 AM
It might seem funny, but I convert decimal measurements back to fractional much of the time mentally. If faced with 0.5781", I'll process it as around 5/8".

Fractions and decimals are part and parcel of the Imperial system, and flipping back and forth between them is not a problem for me. If a drawing is dimensioned in fractions, it infers the dimensions are non critical, and the parts are to be made to fit one another.

On the other hand, I find most metric dimensions meaningless, as I have to convert them back to Imperial for them to have any reference to me. 93.28mm is totally irrelevant to me unless I mentally divide by 25, and then I can think of it as between 3-1/2" & 4".

Much of the time, plans, especially for the HSM, are not cast in stone, and can and should be freely modified to take advantage of materials at hand, or add the builders own modifications. For that reason, many are not much more then refined sketches, and fractional dimensioning is adequate.

Engineering drawings, on the other hand, should be done in decimal dimensioning, as the fits and tolerances are inferred in the dimensions and number of decimal points they are carried out to. If the parts made are for multiple pieces, those dimensions are cast in stone.

When first inspecting plans, all dimensions should be reviewed, and their importance determined. I think, with the increasing use of canned drawing programs, there is a tendency to allow the program to do the dimensioning. This can result in unnecessarally tight tolerances to end up in the drawing.

speedy
04-01-2007, 08:39 AM
I fully agree with you Will.
Not wanting to start a imperial / metric war again .

It could have started already :D

J Tiers
04-01-2007, 08:43 AM
In case it matters, US folks have the same reaction.......

Somehow, the rest of the world believes that the US uses fractional inches, which is completely wrong.

In fact US "engineering" drawings UNIVERSALLY use decimal inches, when they don't use meter/mm dimensioning.

The WOODWORKERS use fractions, largely because they can't buy a tape measure in decimal, and the wood is dimensioned (very loosely) in fractionals. It is also traditional and woodworkers are worse than cats for tradition. Plus, it does not matter much for parts that don't have tolerances and multi-part buildups that are critical. A bit over or under overall is no big deal to woodworkers, they adjust.

I HATE fractional inch dimensions, and can't figure out why anyone uses them for items smaller than houses.

Fractions would be at least a bit easier if one simply stuck with 64ths, and used them, but 9/64, 5/32, 11/64, 3/16, etc, etc.... that's bad.

Stock is traditionally dimensioned in fractionals, probably to avoid being too specific about size. While each fraction has a spcific size to any number of decimal places, it is traditional to consider something like stock (or wood thickness) accurate only to a rough degree if given as 3/4" or whatever.

If it were given as 18mm or 0.750 inch, it would appear to be more accurately held than as 3/4". (another tradition)

Swarf&Sparks
04-01-2007, 08:50 AM
"with the increasing use of canned drawing programs, there is a tendency to allow the program to do the dimensioning. This can result in unnecessarally tight tolerances to end up in the drawing."

Agreed, JC, but I'll tell you another tale of woe regarding a young "engineer" and a CAD drawing.
This was told to me by an engineer mate (combustion) of the old school.

The plant I know, it's just up the road. Aforementioned young engineer was told to knock up a quick drawing of a small part, a gas igniter bracket for a heat-shrink oven. A large heat shrink oven for pallets of bagged powder. The original aluminium bracket was not up to the job and he was told to spec it in 316.

The part duly arrived, along with a \$4500 invoice. (just the bracket, not the gas burner). Beautifully machined part, in G11 Ti.

The young guy doing the drawing had just dragged up an old CAD file and annotated it "Titanium"

The job was for the Ti-Di bagging line!

Weston Bye
04-01-2007, 09:18 AM
I agree that engineering drawings should be dimensioned decimally, but...

Materials are still sold in fractional sizes. Some of the parts I design require nothing more than cutting to length and facing, the mill finish and dimensions being suitable for the application.

Also, it is easier to call out a "3/16 drill" rather than ".1875 dia." if all that is needed is a 3/16 drilled hole. The four decimal places in the decimal callout could be interpreted to require extra precision.

All that being said, the drawings I submit for articles in HSM and DM generally recieve edits for before going to print, so I have been comparing the submitted vs. published drawings to learn where my style (or lack of) differs with that of the editor. I am trying to adjust, to minimize the time the editor needs to spend tuning up my drawings, but old habits die hard.

bob308
04-01-2007, 09:33 AM
if that is the only thing that worries you you are lucky. i have worked where most people have not even been able to read a tape measure. and that was in a fab shop. one guy could only read little lines. you wanted 3/16 you had to say 3 little lines.
i went one place for a job and on the written test they only went as small as 1/8 becaus so many can not read smaller. i guess it goes back our school systems not teaching any more.

Evan
04-01-2007, 09:53 AM
Also, it is easier to call out a "3/16 drill" rather than ".1875 dia." if all that is needed is a 3/16 drilled hole. The four decimal places in the decimal callout could be interpreted to require extra precision.

Not around here. I lay the dial calipers to the drill bit and measure to make sure I have the right drill size.

Weston Bye
04-01-2007, 09:58 AM
Not around here. I lay the dial calipers to the drill bit and measure to make sure I have the right drill size.

Just good shop practice.

TGTool
04-01-2007, 10:00 AM
Back when I was doing mold design, we drew molds around the engineering drawing of the part. But the mold dimensions will be different to take into account draft and shrink. One of the first things I did with a new part drawing was to program the calculator for INPUT times (1 plus shrink factor), and pencil in new dimensions for everything on the drawing. In other words, multiply all the final dimensions needed on the part by the amount of the shrink factor to get corresponding mold dimensions.

I think that's what I'd do with an all fractional (or metric) drawing that hacked me off. Quickly get to dimensions that work in my head.

Swarf&Sparks
04-01-2007, 10:01 AM
"I lay the dial calipers to the drill bit and measure to make sure I have the right drill size."

Same here Evan, unless it's one of the pairs (drill and tap) I keep separate in a drawer.
Even when my eyes used to work a little better than they do these days, I'd check :(

wierdscience
04-01-2007, 11:12 AM
Decimal inches are the norm,but a calculator solves the fractional problem.I typically go over a print and make my own rough sketch with decimal inch notes on it before I do anything even if the print is metric.

I only see prints with fractios on them from one old (Noah's ark era)company that makes steam pumps.I guess they figure if the prints have worked since 1870 why change them.

Checking tools with a caliper first is a good idea,you learn to do it quick when working in a shop with multiple people.Just because a drill is in the 27/64" slot doesn't mean it's a 27/64:mad:

Milacron of PM
04-01-2007, 11:22 AM
Here's the solution !

http://www.woodcraft.com/images/family/web4440big.jpg

:)

There is a company that makes digital readouts that display fractions as well. They sell to woodworkers mostly, like for adding a thickness scale to your surface planer or length scale to your radial arm saw.

ckelloug
04-01-2007, 11:23 AM
Standard Y.14M drawing practice in the name of Evan's concern about the 3/16 hole would be this:

http://i161.photobucket.com/albums/t202/ckelloug/dim.png

BobWarfield
04-01-2007, 11:24 AM
That's it!

It's the woodworkers that have started all this fractional nonsense!

Here and I thought it was a plot by the Chinese to wreck productivity in our shops.

Best,

BW

tyrone shewlaces
04-01-2007, 11:28 AM
OK if a drawing is completely in fractions, then that is probably just a stupid choice.

But hasn't anybody else here ever run across a tolerance block?
.xxx = +/- .005"
.xx = +/- .015"
Fractions = +/- .030
(or whatever)

In a shop where this is actually paid attention to (not yours??) then including fractions in a drawing is very intentional and useful to the machinist down the line.
As with anything not used regularly, fractions take a little thought at first, however little. If you had to look at drawings every day which include fractions, after a while it would be so effortless you would wonder why anyone would be angry at the guy who put them on the drawing, at least providing their inclusion had purpose.

ProGunOne
04-01-2007, 11:44 AM
Whew, I thought this was another (mis) spelling rant. ;)

ronm
04-01-2007, 11:45 AM
I have a 6" caliper, made by General, that I bought at the hardware store when I was in Jr. high, I think. It's graduated in 16ths & 32nds, but actually has a vernier that splits 16ths into 8 parts...interesting, but I've never run across a print dimensioned in 128ths...also still have a Henry L. Hanson "Ace" micrometer I bought along about the same time, & learned to read a mike. I think I paid 5 bucks or so for it...the good ol' days...
Ron in CO...

Marc M
04-01-2007, 12:04 PM
Most of the time I'm redrawing the print so the use of fractions isn't a big deal. The bigger problem I run into is the prints are dimensioned willy nilly from the nearest surface, the third hole from the left, etc. Also, there's usually a critical dimension or two missing to make room for some unnesessary ones. I redraw the prints and dimension them from a single datum point, or another feature if required, always from the standpoint of how I'm going to make the part. I also add additional data such as drill/tap info so everything I need is on the print. I've been using AutoCAD since the days when an XT was cutting edge technology so I can draw pretty quickly. The amount of time I save at the machine not having to interpret poor drawings usually outweighs the time it took to redraw. It also goes a long way to prevent mistakes. Once it's in the computer, I can print out as many copies as I need and I'll never lose it.

kendall
04-01-2007, 06:11 PM
I normally do it the way Mark described, redraw and redimension Ran into too many that left huge gaps in layout, some you'll not find out about till you have everything ready to go. Last one was for a tweak bar on motorcycle forks, everything was there, bolt size and thread, type and thickness of material etc, no mention of the fork tube size or center-center distance.

Worked at a bank a while ago, one dimension on the print was noted as being a 'hammer fit' to enclose a control panel. All the elevations on that print were marked from SEA level. Which for some reason confused the crap out of most of the crews there. Electricians, plumbers, and communications were all scratching their heads, I just read the sea level measurement for the floor and subtracted that from the rest.

Ken.

scott96088
04-01-2007, 06:36 PM
OK if a drawing is completely in fractions, then that is probably just a stupid choice.

But hasn't anybody else here ever run across a tolerance block?
.xxx = +/- .005"
.xx = +/- .015"
Fractions = +/- .030
(or whatever)

In a shop where this is actually paid attention to (not yours??) then including fractions in a drawing is very intentional and useful to the machinist down the line.
As with anything not used regularly, fractions take a little thought at first, however little. If you had to look at drawings every day which include fractions, after a while it would be so effortless you would wonder why anyone would be angry at the guy who put them on the drawing, at least providing their inclusion had purpose.

I see this all the time on drawings I bid on and parts I make for several companies.. I'm glad you posted a sample,. It's also I guide line I use when I make a drawing for self use.

Scott

Elninio
04-01-2007, 08:18 PM
keeping it as a fraction is more precise, sometimes when you have odd fractions converted to decimals you have a lot of digits which sometimes get ommited (accidentally, or simply because there is not enough room on the drawing)

doctor demo
04-01-2007, 08:22 PM
I have a 6" caliper, made by General, that I bought at the hardware store when I was in Jr. high, I think. It's graduated in 16ths & 32nds, but actually has a vernier that splits 16ths into 8 parts...interesting, but I've never run across a print dimensioned in 128ths...also still have a Henry L. Hanson "Ace" micrometer I bought along about the same time, & learned to read a mike. I think I paid 5 bucks or so for it...the good ol' days...
Ron in CO...
Weren't they called General Stores,and one room school houses back then?:eek:
steve:D

Tin Falcon
04-01-2007, 08:37 PM
The following is quoted from SHOP THEORY , Henry Ford Trade School, Dearborn Michigan, Published by McGraw Hill Books 1946 Printing.

Chapter 1 Beginning. ”The measurements made in a machine shop are usually taken in inches or fractional parts of an inch. Most of the precision tools in the shop read in thousands of an inch. The usually graduation on a rule are in 64ths, 32nds, 16ths, and 8ths of an inch.
Before a student can read a rule or the precision measuring tools efficiently, he must be thoroughly familiar with fractions and decimal fractions. Since he is often called upon to change decimals to fractions and fractions to decimals in making measurements, and in reading and checking blueprints and sketches. He should understand this operation thoroughly. …… Memorize the quarters, eights, sixteenths, one thirty-second, three thirty –second and one sixty-forth.”
IMHO this is one of the basic foundational skills of being a machinist. When I went to trade school in the Air force we had to memorize the decimal equivalents for ½., ¼ , 1/8 , 1/16, 1/32, and 1/64.
As far as basic tolerances I learned that the basic tolerance on fractional dimensions is +- 1/64.
Regards
Tin

john hobdeclipe
04-01-2007, 09:26 PM
When I first started to work in a furniture factory, we measured length, width and thickness to the closest 1/16 inch. Other aspects of a piece, such as dowel hole locations were done by fitting to an approved master pattern. This was precise enough for upholstry frames.

Later, in the bicycle business, I was exposed to and started learning to metric measurements.

Then, back in the furniture business, at a major player in the high end case goods market, we managed to get by with + or - 1/32 inch.

Still later, I found myself setting up and operating German built Weinig moulders, which are all equipped with metric scales and dials. So we would always get drawings dimensioned in fractional inches, we were supplied with dial calipers graduated in decimal inches, and used these to set up machinery graduated in metric. I soon became very adept at mentally converting between the three without really having to think about it.

Carl
04-02-2007, 12:11 AM
If faced with 0.5781", I'll process it as around 5/8".

.625 minus .5781 = .0469...pretty loose tolerances there...:D

Evan
04-02-2007, 02:41 AM
keeping it as a fraction is more precise,
Not really. There are infinitely more irrational numbers than rational numbers. Fractions cannot be used to represent irrational numbers such a pi, phi, e or sqr root of 2.

Furthermore, fractional denominators as commonly used in measuring are a binary system based on powers of 2. You don't normally see fractional dimensions such as 1/3 or 1/5 or any other odd denominator which limits what can be represented via fractional measurements.

wbleeker
04-02-2007, 03:40 AM
I certainly opened up a can of worms here! I just think it would be easier on everyone if measurements were in decimals because it would save having to convert them, drill sizes are set so that is no problem, if the drawing say's drill 3/16th that is what you do and as for those bloody stupid verniers that read in .128ths, have any of you ever tried to buy any kind of a spare part for anything when the bloke behind the counter thinks he can read the bloody thing!
Will

Mcgyver
04-02-2007, 06:57 AM
it may be a pita, but is convenient. ok, on a simple drawing, there isn't much point, but on complex drawings, you are often required to sum dimensions. the sum might be 2.375, easy to interpret, but there may be some 3/32 or 7/64 along the way - created btw by the ever common design need to bisect things, something the French and their metric didn't think of, but then again the developed the system for cooking not engineering :D

so its easy to add 32'nds or 64'ths but decimals wouldn't work. you'd either be rounding off so it would not accurately sum 2 and 3/8, OR you'd be over stating the number of significant digits leading to poor homeshop guys trying to work to a millionth of an inch.

Will I've cursed with you, but fractions are practical and lesser of two evils on a drawing.

kap pullen
04-02-2007, 07:48 AM
In the good old days, readouts were not avalible.

Most drilling, and milling operations were laid out with scale, square, dividers, and surface gage.

Most jobs were machined with the the same scale, square, and Id and od calipers.

Many casting kits today date from those times (not that long ago).

Bolt circles were called out like 6 holes on 3 3/8 bolt circle. The holes were 1/16 oversize for clearance with the mating parts.

They were laid out with the scale, and dividers.

In many shops, the layout man was a full time occupation, and one of the top rated craftsman in the shop.

The holes were located from different sides, and surfaces, drawn as the parts worked in assembly.

Today holes should be called out from the same datam points to eliminate calculations on the shop floor. Calculations mean time and mistakes.

Holes, I believe, should be specified in a table with x, and y, dimensions
and hole discription.

This cleans up the drawing eliminating the "rats nests" common on many drawings.

How many times I have seen two, or three machinists in a huddle, trigging out a bolt circle.

Oh yea! one of the first tasks we had as "dumb f... apprentice boys" was to learn fractional, and decimal equivalents.

Whatever you say, the engineers will do it their way, for whatever their reasons happen to be.

The home shop guy may have readouts, or not. I have found the home machinist to be more flexible, and inventive in finding ways of doing things.

Kap

JCHannum
04-02-2007, 07:55 AM
.625 minus .5781 = .0469...pretty loose tolerances there...:D
The statement was referring to processing a dimension mentally, not physically working to that number or tolerance.

When looking at or hearing a dimension, one mentally asigns a size to it, or describes it by holding his fingers apart. I process fractional dimensions in that manner. 37/64" is "about that big", ie more than 32/64" but less than 40/64" and closer to 40 than 32. That process is done subconsciously.

The problem I have with metric dimensions is that to visualize a dimension, I first have to convert it to an Imperial dimension. That has to be done consciously by dividing or multiplying by a fudge factor. Metric dimensions are also further confused by the deci-, milli- and other descriptors added, requiring another step to decipher the size.

It is not a problem as much as an annoyance. Dimensioning is like a language, and you speak and think in the language you are most familiar with. If you use two languages on a regular basis, you will speak and think in either language. Similarly, if you use fractional, Imperial and metric dimensioning on a regular basis, you will speak and think in either with little difficulty.

Paul F
04-02-2007, 02:01 PM
I was taught pretty much the same as Tyrone...

If I see a 4th place decimal, it meant it has to be +/- .0005. unless otherwise specified.
If I see a 3rd place decimal it meant it has to be +/- .003 unless otherwise specified.
If I see a FRACTION, get it in the general vicinity and call it good.

So I automatically think when I see a hole callout as ".5000" that I better drill undersize, ream slighly undersize, and lap the hole to .5000".
IF I see a call out of .500, I drill undersize, and ream the hole to .500.
If the print says "1/2""... I grab the 1/2" drill and drill the damn hole.

Now, if the print says "hole 1/2" +/- .0001", THEN I agree... it was a stupid way to make the drawing.

Paul F.

04-02-2007, 04:45 PM
I solved the problem by memorizing ALL unit conversions. Want a conversion from femto-seconds to presto hemi-semi-demi quavers to the base 16? I can do it. Belgain barleycorn measure to Chinese li? No problem. What? Can't everyone.

The one exception is the Female concept of frequency: "You always the leave the toilet seat up!" (did it twice) "You never remember my birthday!" (forgot once). I can:

- Do units conversions and trigonometry to 6 decimal places in my head

- Run an organization the size of NASA from jottings on the back of an envelope.

- Work out the most efficient routing for mail and parcels in the US on any particular day.

- Memorize the whole tax code and relevent case law.

- Never get lost in the most bewildering environment including limestone cave systems.

- Understand but not completely formulate the relationship of mass, energy, and the universe.

But I will never get the Female concept of frequency.

Joel
04-02-2007, 05:51 PM
Seems like you have it nailed to me. Once = always (mood dependent, of course).

Women; you can't live with them, you can't have heterosexual sex without them.

Evan
04-02-2007, 06:53 PM
Women; you can't live with them, you can't have heterosexual sex without them.

There are plenty for hire.

kendall
04-02-2007, 07:31 PM
There are plenty for hire.

Seems like it would be cheaper that way.

I think of all the things I've had to play with in life, my girlfriends have been the most expensive. tools, cars, motorcycles, machines etc, much cheaper than my wife. And if I don't play with them for a while they don't complain.

Ken.

Tin Falcon
04-02-2007, 08:14 PM
Will:
Interpreting drawings can be a PITA . I remember a few years ago I had started a new job. I was given a drawing in fractions. Like discussed earlier fractional dimensions mean +- 15 thousands. I was later told the parts I made were not close enough. I later found out that the owner that did most of the drawings was the son of an architect so he thought he knew how to prepare drawings. Later I was doing a job with bolt circles I did the math so I had the dro coordinates . The shop foreman was amazed as they had always laved out bolt circles by hand with scribes. His comment was gee "I guess that would be more accurate!"
The fun comes when you have a drawing for a model engine. The shaft and the hole in the flywheel and the hole in the crank disk are all dimensioned for 1/4 inch. The fit between the disk and shaft are a press fit and the shaft to flywheel is a slip fit with a set screw. So the 1/4 inch dimension does not necessarily mean .250inch
Tin

wierdscience
04-02-2007, 09:04 PM
Seems like it would be cheaper that way.

I think of all the things I've had to play with in life, my girlfriends have been the most expensive. tools, cars, motorcycles, machines etc, much cheaper than my wife. And if I don't play with them for a while they don't complain.

Ken.

"The three F's"

If it Flys,Floats,or Fornicates it's cheaper to rent:D

dicks42000
04-02-2007, 11:30 PM
Darren beat me to it....'nuff said.

speedy
04-03-2007, 12:50 AM
"The three F's"
If it Flys,Floats,or Fornicates it's cheaper to rent:D

That would be dependant on how frequently you go flying, fishing or the other thing:D

The best thing about fishing is you dont have to talk ( before, during or after)
if you dont want too:)

ronm
04-03-2007, 01:29 AM
"The three F's"

If it Flys,Floats,or Fornicates it's cheaper to rent:D
"If it's got tits, tires, or tracks...it's gonna cost ya"...

wirewrkr
04-03-2007, 10:03 AM
BACk on the subject of the thread, I am one of those quirky aAmericans that was raised on METRIC. (Iwas a bicycle mechanic as a very young man)
Metric is a simple system that also uses a a decimal breakdown.
fractions of an inch are a pain the arse, always seemed antiquated to me.
Robert
My other car is a table saw

Evan
04-03-2007, 12:15 PM
I also learned metric from the start along side of imperial measure. My dad was a scientist and science teacher and metric has always been the measuring system of science (except in NASA). I really don't care what system I am using. I needed some 8-32 screws the other day and they didn't have any. A quick calculation showed that .8 mm pitch is 31.75 TPI and that a 4mm x .8 pitch metric screw is only a few thou smaller in diameter than an 8-32 screw. Close enough for what I needed. Same goes for 6-32 and 3.5 mm x .8 pitch. Only .000205" difference in diameter. I use standard metric 3.5mm x .8 screws from computers all the time in place of 6-32.

Marc M
04-03-2007, 12:19 PM
The one exception is the Female concept of frequency: "You always the leave the toilet seat up!" (did it twice) "You never remember my birthday!" (forgot once).

Keep in mind that Female frequency is inversely proportional to the gender...

"I never buy anything for myself!" (unless it's jewelry, clothes or shoes and the sun rises that day)
"I always have to pick up your dirty clothes!" (happens once or twice a year)

As far as Imperial/Metric goes, I'm Bi. Since all my calipers and DRO switch back and forth, I can work in either system just the same. I don't have metric mics so if I have to get mic close I do have to convert, but most of what I'm doing isn't that close.

If I'm working with an existing part, I always work in whatever system that part was made with. Using decimal with a metric produced part yields all sorts of oddball numbers. But if I use metric instead, the goofy numbers become 4mm, 8.75mm etc. I find it's a lot easier to deal with numbers that make sense.

loose nut
04-03-2007, 08:05 PM
BACk on the subject of the thread, I am one of those quirky aAmericans that was raised on METRIC. (Iwas a bicycle mechanic as a very young man)
Metric is a simple system that also uses a a decimal breakdown.
fractions of an inch are a pain the arse, always seemed antiquated to me.
Robert
My other car is a table saw

Both systems are decimal inch-.001" or metric-.01mm, therefore there is no superiority of one over the other, at least not in the shop, as for threads, you don't need to know all the dimensions of the thread just the designation IE: 6-32 or M4*1 etc. again there is no superiority of one over the other. I was schooled in both systems and I hate metric, the pro metric crowd is always telling us of the advantages but there are a lot of disadvantages in that system too, using the MM as the standard unit is one, it's to small. If the CM had been used , like many of the old metric countries wanted, it would have made more sense. Also, the pro metric crowd is always throwing the fraction card out, how many machinist that use the imperial system adjust the cross slide by 16's or 64's, they don't, so there isn't any validity to that argument either. When the US finally goes metric the imperial system will still be around for a long time because of the need for backward comparability with existing equipment, long after we will be pushing up daisies.