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BigBoy1
05-08-2007, 09:18 AM
I'm involved in my first big project where I'm making the drawings and then machining the items. I'm really getting fed-up with the darn fractional dimensioning system. It really is not a user friendly system. Also, as I understand, it was fostered by the wood workers and it has been addopted by metal workers.

My question is why don't "they" make machining tools, i.e. milling cutters, drills, etc. in even numbered decimal inches? Instead of specifing a 3/32", why not use a tool 0.100" in dimension; a 0.200" tool instead of a 13/64", etc.? It sure would make dimessioning much easier and halfing if dimensions a whole lot easier.

Just my ramblings on this rainiong morning!!!!

Bill

paulx
05-08-2007, 09:27 AM
Why not go metric.

BobC
05-08-2007, 09:37 AM
Ditto on the metric. It would be so much simpler.

dirty old man
05-08-2007, 10:21 AM
For those of you who are young, just starting out in the world of machining and otherwise working with tools, and other things to which measurements apply, I'll grudgingly admit that metrics could be a good way to go.
But to old farts like me (next birthday will be 70), metrics are a PITA and a costly thing.
After a lifetime of gathering tools, machines, etc. now I am having not only to learn metric measurement, but buy tools, machines, etc. again or be left in the dust.
All sorts of wrenches, many of them expensive special ones won't work on newer vehicles because of metrics, mics and other measuring tools are a PITA to use as you must convert the dimensions or the measuements, drill bits, reamers, taps, dies, and the buckets of bolts you have collected in a lifetime are useless.
And to top it off 3 perfectly good lathes are becoming obsolete because they don't cut metric threads and it would take more labor than they are worth to design and build conversions for them.
No, I don't think you want to ask me what to do with metrics.
Dave

Swarf&Sparks
05-08-2007, 10:51 AM
Unless you plan to try single point threading in metric, on an imperial lathe; why worry?

It's about time the USA got over its aversion.
I prefer to grab a 12mm drill but I can still use a 31/64 in a pinch.
It's a lot easier on my 50 YO eyes, to read calipers (yes, verniers) in 0.01mm for a quick check than all the confusing lines on the inch side.

Lest you think I'm some euro Jean-come-lately, I grew up with and am comfortable in both systems.
The grief comes when you try to convert.
Worse still, is when you change horses in mid-stream.

Regards, and good luck with the project,
Lin.

pcarpenter
05-08-2007, 11:23 AM
I'm not sure how we got from fractionals vs. decimals all the way to completely switching systems of measurement. I'm also one of those folks who grew up with both and it clearly did not *reduce* the number of things I gotta know. In addition to knowing that 1/16=.0625, I have to know that 2.54cm= 1 inch. That's more difficult, not less. There is a saying that says "that's the great thing about standards....there's so many to choose from". We didn't get a replacement standard when we here in the US tried to adopt the metric system, we got *another* standard.

The trouble is that "Embracing" the metric system will inherently be a switching of horses mid stream. We have lots of stuff like machine tools, indicators, etc that would all have to be replaced and that is no small matter.

I guess I also don't understand your statement about single point threading (is there really any other kind for most of us?) on an imperial lathe. Many of us have imperial lathes. We do single point threading. If we "embraced" the metric system, we would need to be cutting metric threads on that imperial lathe....which was exactly the point.

Heading back to the original topic, however, the use of standard fractionals is not so terribly difficult. If a decimal equivalent chart (I have them on about every wall in my shop) is not your bag, learn the standard values for the lowest fractional increments and then you just need to add and multiply.

ie. 1/8= .125, 1/16= .0625 etc. From those you can know that 9/16=.5+.0625 or .5625 without the aid of a table. After working with them a bit, all the common stuff will be in your head anyway.

paul

Swarf&Sparks
05-08-2007, 11:56 AM
Kinda my point, Paul.
If you are designing a part you have to single-point, you use the native system of your machine. If you are just drilling and tapping holes, or measuring and cutting, use what you're comfortable with.

Me, I stick with metric coarse. M4, 6 & 10 taps and dies cover 99% of what I do. And fasteners are available in almost any head and material, just up the road.

OK, I confess. I'm using 1/4 20 UNC allthread feed screws on my little CNC engraver/router :D

J Tiers
05-08-2007, 12:51 PM
Well everyone knows that imperial measurements are ONLY in fractions.

Everyone knows that IS what the US system is, and is why it is so difficult to work with US/Imperial measurements.

Everyone knows that Metric solves that problem by using decimals.

Everyone knows that you CAN'T use decimals in the imperial system, it is impossible.

That's what everyone knows................

The rest of us wonder why anyone would use fractional measurements when all the dials on your machine are calibrated in decimal inches.

The rest of us wonder why anyone would use fractional measurements when all the dials on your dial calipers and micrometers are calibrated in decimal inches.

The rest of us wonder why anyone would use fractional measurements when US metalworkers have used decimal inches (or metric, yes) for 100 years. :rolleyes:

Swarf&Sparks
05-08-2007, 12:54 PM
Yup, and still make 31/64th drills

John Stevenson
05-08-2007, 03:52 PM
When China decides to only supply in metric to simplify production to the rest of the world, the US will have to change, after all if it's not manufacturing anything it can't support imperial.

OK only said in jest but what would happen if HF, MSC, Jet and Grizzly were only able to source metric machines from China ?

When I was over in China, on the Seig stand they had a C4 lathehttp://www.siegind.com/Products/pic/br-c4_new.jpg

Nice little thing, 8-1/4" swing by 18 between centres, power to carriage and cross slide but it was all metric.
I asked about an imperial version for the UK but was told no. I then pointed out that they needed an imperial version for US markets but their answer was metric or don't bother, they can sell enough in metric countries not to warrant having two models.

.

topct
05-08-2007, 04:36 PM
Thats a very nice looking little lathe John.

If I had one I would not care that it was metric.

I have measuring tools that will tell me what size something is.

J Tiers
05-08-2007, 04:43 PM
How many extra change gears do you need with a metric lathe for gear cutting?

Because everything is pitch based, ther isn't the same relation between thread pitches that there is with an "X per unit measure" system.

Seems that to get all the pitches at 0.5mm, 0.6mm, 0.7mm, 0.8mm etc that you would not get the ability to have a wide range QC box as with a TPI (TPmm? TPcm?) system.

topct
05-08-2007, 05:10 PM
"How many extra change gears do you need with a metric lathe for gear cutting?"

If a transposing gear can be created to cut metric threads on an imperial machine, can't one be made to make a metric machine cut imperial?

John Stevenson
05-08-2007, 05:21 PM
Yes I did take a picture of the threading chart on the C4 but having a bit of a problem uploading it.
It's the same 127 gear required as for doing metric on an English lathe and the C4 is equipped with that so.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/c4_%20table.jpg

Sorted..

.

aboard_epsilon
05-08-2007, 05:21 PM
There you go guys, get practising !

http://www.thinkmetric.org.uk/index.html

nice quiz there also ...to see if you've taken it all in

So follow the rest of the world !

And don't go crashing on mars :D

And send NASA a link to the site above.

all the best..mark

HTRN
05-08-2007, 05:29 PM
[cranky old man]The metric system is the tool of the Devil! My horseless carriage gets 150 rods to the gill, and that's the ways I likes it![/cranky old man]:D

HTRN

BobWarfield
05-08-2007, 08:37 PM
[cranky old man]The metric system is the tool of the Devil! My horseless carriage gets 150 rods to the gill, and that's the ways I likes it![/cranky old man]:D

HTRN

So then you'd need a 75 tooth gear instead of the 127 that's used for metric.

Best,

BW

rbregn
05-09-2007, 12:00 AM
The lathes they are using here in nanjing will cut inch threads..............all except 13tpi!! the one I use the most of!

Milacron of PM
05-09-2007, 12:14 AM
A profound irony in all this is that the King of all things Chinese, Harbor Freight doesn't sell metric screws ! Check out their hardware assortments sometime....they have a few metric things, like metric O ring sets...but no metric bolts, cap screws, nuts, etc

Also ironic that the folks that do sell metric screws usually have the prices higher than SAE...whereas one one think they would be *cheaper* in reality...since the actual worldwide production of metric fasteners is way higher volume than SAE.

darryl
05-09-2007, 01:52 AM
Well, maybe a few known and well used units of measurement will remain as standard for all systems of measurement- like tad, nats whisker, c-hair, etc.

And who the heck are 'they'? I bet even 'they' don't know who they are. They all know what they are though. A bunch of a holes.

John Stevenson
05-09-2007, 03:32 AM
Also ironic that the folks that do sell metric screws usually have the prices higher than SAE...whereas one one think they would be *cheaper* in reality...since the actual worldwide production of metric fasteners is way higher volume than SAE.

Don,
It's called exploitation :D
We had the same here when we were imperial / Whitworth, even though at that time SAE was in greater production due to being used on most vehicles we paid a premium.
Now we are metric we see cost savings but SAE is virtually unheard of now in the UK as there are very few US vehicles here and all imports are metric.

Rbregn,
The reason 13 is often missing from machine threading is that it's a special to the US. When Mr Whitworth did his studies on the best thread forms and standardised on the Whitworth range others copied with slight alterations. The US for instance changed from 55 degrees to 60 just to have their standard but kept the same pitches except the 1/2" x 12 which they changed to 1/2" x 13 for some reason.
Ironically though the US then went on to make various lathes over the years that couldn't do 13 threads.

Even more ironic is that the original copiers of the world, the Japanese followed by the Taiwanese, then China copied the Whitworth thread and then imported it into the US. This is why we keep getting these post about Chinese and Taiwanese mill/ drill with 'special' 1/2 x 12 threads.

There is nothing special about 1/2" x 12 it's just took 170 years to come back and bite you :D

.

speedy
05-09-2007, 04:17 AM
I'm involved in my first big project where I'm making the drawings and then machining the items. I'm really getting fed-up with the darn fractional dimensioning system. It really is not a user friendly system. Also, as I understand, it was fostered by the wood workers and it has been addopted by metal workers.
My question is why don't "they" make machining tools, i.e. milling cutters, drills, etc. in even numbered decimal inches? Instead of specifing a 3/32", why not use a tool 0.100" in dimension; a 0.200" tool instead of a 13/64", etc.? It sure would make dimessioning much easier and halfing if dimensions a whole lot easier.
Just my ramblings on this rainiong morning!!!!Bill

Well, if your drawing and machining then dimension in whatever system you wish. Convert fractions to decimal divide numerator by denominator. I grew up with imperial `till 67 when we converted to metric and I am at ease with either.
I must say though, that it is long past the time that the rest of the world got into step with the American system:rolleyes:
As an aside but sort of related; why do our American cousins quote thread sizes as 8/32 for example, instead of 1/4"?

The Doctor
05-09-2007, 04:22 AM
BigBoy1, get a chart or memorize the decimal equivalents. Failing that, perhaps get a hobby that requires less brain power:D Seriously, in most hobbies/lines of work there are things you need to learn. In machining you have just discovered the first of many.

Good luck
Ed

speedy
05-09-2007, 04:43 AM
Good advice Ed. Bill, get yourself a Zeus book, very handy.

J Tiers
05-09-2007, 08:03 AM
"How many extra change gears do you need with a metric lathe for gear cutting?"

If a transposing gear can be created to cut metric threads on an imperial machine, can't one be made to make a metric machine cut imperial?

Of course yes, THREAD cutting...... got gears on the brain....

At any rate, by looking at distance advanced, instead of X threads/Y distance, one comes up with all sorts of odd ratios, even though the actual pitches are at "standard" intervals.

John S' table is for a change gear machine, I was more asking what change gears have to go WITH a QC machine to adapt to all teh various pitches.

Lew Hartswick
05-09-2007, 08:34 AM
As an aside but sort of related; why do our American cousins quote thread sizes as 8/32 for example, instead of 1/4"?
That ISN'T 8/32 it's 8 -32 as in number 8, 32 threads per inch.
One of my "pet peeves" is people who do just as you did. :-)
...lew...

05-09-2007, 08:51 AM
I don't even notice the fraction Vs decimal tension. At an early age I memorized the decimal equivalent charts to 1/16" and can estimate very closely by adding or subtracting 0.032 or 0.015 to get the 1/32" and 1/64 over or under the nearest 1/16". Took about a week as I recall and it's refreshed almost every day in the course of routine work. Just in case there's a handy fractional/decimal/tap drill/metric chart on the wall. On my comouter I have a function that converts any or all dimension to fraction, decimal, metric whatever in a single click.

I don't know what the fuss is about. You do a little memory work early in the game like you do for multiplication tables, trig functions, telephone numbers, song lyrics, birthdays, anniversaries, auto and sports stats, etc.

japcas
05-09-2007, 08:53 AM
Bigboy1, I couldn't find in your profile where you are located. There is an old saying that says when in Rome do as the Romans do. If you are in the U.S. get used to the fractions and the decimals. If you are located somewhere that uses metric all the time then use it. Like Doctor said, this is just another part of the trade and something that you really should learn. Even if not used often it is useful to know how to read the print no matter what system they are using. I work in a shop full time and use all of the systems. It just depends on how the print is dimensioned. With practice you'll be converting fractions in your sleep.

drof34
05-09-2007, 12:21 PM
This is my take on the imperial threading system vs. the metric threading system and I could be wrong( usually am, but if I am I would like to be straightened out). Most of you probably already know this but it might be helpful to some.

The imperial threading system is usually denoted as # of threads per inch which is not the same as the lead. To obtain the lead of one thread the TPI is divided into one inch.

The same procedure(threads per millimeter) is not viable in the metric system since a MM is only~.039". Therefore, in the metric system the lead is denoted directly in the LEAD per MM(millimeters per thread).

Jim W.

J Tiers
05-09-2007, 01:09 PM
This is my take on the imperial threading system vs. the metric threading system and I could be wrong( usually am, but if I am I would like to be straightened out). Most of you probably already know this but it might be helpful to some.

The imperial threading system is usually denoted as # of threads per inch which is not the same as the lead. To obtain the lead of one thread the TPI is divided into one inch.

The same procedure(threads per millimeter) is not viable in the metric system since a MM is only~.039". Therefore, in the metric system the lead is denoted directly in the LEAD per MM(millimeters per thread).

Jim W.

Well, not really...... turns/unit measure is viable in either system.

Your error is evaluating the metric system from the viewpoint of its equivalent dimension in another system. That is not the way to look at a self-contained system.

So 0.5mm pitch is 20/cm, or 2 spindle tuns per turn of a 1mm pitch leadscrew. Or 5 per turn of a more practical 2.5mm pitch screw.

In the "threads per" system, the actual pitch can be a funky number. But its a "don't care" number, so that isn't a problem.

The "threads per" system also lends itself to repeats, 8/16/24/32, 9/18/27/36, etc, which vary by a common factor, so both series can be attained by varying a "set ratio" (the basic leadscrew relationship) and a "series ratio" (the series progression gearing) independently.

The same "series ratio" works with a number of "set ratios" to form logical groups.

By fixing on even intervals of pitch, while you MAY end up with some numbers that work, you also end up with "sports" that don't fit in. It LOOKS so "logical" to the rigid mind, but actually in practice it breaks down.

A 4mm x 0.7 is common, and 0.35mm pitch is OK also, but the next lower pitch in that series would be 1.4mm.

Unfortunately, 1.5mm is standard.....

so you end up with uneven sets.

0.25, 0.5, 0.75, 1.0, 1.25, 1.5, etc are OK.

0.5, 1, 1.5, 2, etc are OK, although they overlap the prior

But 0.3, 0.6, then nothing until 1.5

And 0.35, 0.7, ............... 1.75

or 0.4, 0.8, ............ 2

or 0.45, ..................... 4.5

The "threads per" system tends to work out better for repeating evenly distributed increments, fitting nicely into a QC box design. That is no doubt why it was used.

BigBoy1
05-09-2007, 03:14 PM
I'm in the US in NC. I've done quite a bit of machine work in the metric system and just find it a much easier system to used. Being based upon the 10 number system instead of a system where each of the previous numbers is cut in half, i.e. 1/2, 1/4/, 1/8, 1/16, 1/32, etc., it is a system where changes are made by just moving the decimel point. Converting from millimeters to kilometers is done by moving the decimel point. Quickly calcuate the number of inches in a statue mile.

I was just speculating that a 10 based inch system would be much easier to use. If cutters were made in 0.200, 0.350, 0.475, etc., it would help the conversion process. Also, if people got use to a 10 based inch measuring system, conversion to the metric system would be much easier and understandable.

The US Congress has been studying the conversion to the metric measurment system since 1798 when they formed a study group to look into the conversion to metric. At the rate Congress moves, they still must be "studying" the problem!

If con- is the opposite of pro-, then is congress the oppsite of progress?

Bill

mayfieldtm
05-09-2007, 04:10 PM
These days with calculators and computers, the Base or System being used is not all as important as in previous days.
Time was even a pencil was a luxury and calculations for making things were largely done in the head.
Also, in the real world, materials are most efficiently used if when divided or cut up, it was done so in whole units, I.E. divide by 2 or divide by 3.
Example, if I need to make two big signs out of a sheet of plywood, I would just cut it in half to get two 4' x 4' pieces. I probably would not go to the trouble to make them 47" by 47".
This is where Fractions shine.
It is also no mistake that base 12 existed, as in inches and feet.
12 can be evenly divided by more numbers than others (divide by 2,3,4 or 6).
Base 10 can only be divided by 2 or 5.
This is why the Packaging Industry uses Base 12.
A 10 pack of beer can't be divided evenly between 3 persons.
Problems arise when converting between Bases or Systems, then again, not difficult with the calculator or computer (unless you work for NASA).
We will probably never have just one system. They all have their advantages.

Tom M.

J Tiers
05-09-2007, 04:57 PM
I still have no idea why this deal of fractions still comes up......

Cutters are easily obtainable in 0.500 inch and 0.250 inch, if you really don't want any odd fractions, or their decimal value, to ever sully your process sheets.

But, since 1/8 is 0.125, and 3/18 is 0.1875, etc, it seems that obsessing on the cutter size is unprofitable.... tables exist...... and options do also.

And, naturally, as mentioned the dials on every machine I know of are decimal inches..... not exactly a new development, probably date back to 1870 or so..... And, machinists scales always have decimal inches (and often fractionals on the reverse, too)

Can someone please remind me just why this "inches always = fractions" deal continues to come up?

ligito
05-09-2007, 05:47 PM
"This is why the Packaging Industry uses Base 12.
A 10 pack of beer can't be divided evenly between 3 persons."

And a 12 pack can't conversely be divided evenly among 10 persons.

The guy that goes for the beer just stashes anything leftover, for himself.
:D

AJL
05-09-2007, 07:12 PM
What measurement is easier to work with, .001 inch or one-fiftieth mm? Why not .01 mm? Too small a unit to be practical for setting for most tolerances? Or .1 mm? Too large a unit? I admit being pretty ignorant of the metric system, but as I recall most common measurements in that system are to fiftieths of a mm. Seems an awkward unit to me. AJL

J Tiers
05-10-2007, 12:16 AM
What measurement is easier to work with, .001 inch or one-fiftieth mm? Why not .01 mm? Too small a unit to be practical for setting for most tolerances? Or .1 mm? Too large a unit? I admit being pretty ignorant of the metric system, but as I recall most common measurements in that system are to fiftieths of a mm. Seems an awkward unit to me. AJL

and how would THAT be?

Just as decimal inches are as common as dirt, so 1/50 mm are as well. While you CAN express it as one of the hated fractions, you certainly don't have to.

Remind me again why 0.02mm is strange?

speedy
05-10-2007, 01:49 AM
That ISN'T 8/32 it's 8 -32 as in number 8, 32 threads per inch.
One of my "pet peeves" is people who do just as you did. :-)
...lew...

Thanks for the clarification Lew; and hey, this might help :)
http://www.mypetpeeves.com/

AJL
05-10-2007, 07:18 AM
and how would THAT be?

Just as decimal inches are as common as dirt, so 1/50 mm are as well. While you CAN express it as one of the hated fractions, you certainly don't have to.

Remind me again why 0.02mm is strange?

It's not just strange, it's weird. One thousandth of an inch seems a tidier unit to me. As a matter of curiousity, when you want to measure to, say, 2.023 mm, how do you express it in words? AJL

J Tiers
05-10-2007, 08:06 AM
It's not just strange, it's weird. One thousandth of an inch seems a tidier unit to me. As a matter of curiousity, when you want to measure to, say, 2.023 mm, how do you express it in words? AJL

Um.....

The same way you would express 2.023 inches, only you say the word "millimeters" instead of "inches".............

I once worked with a woodshop supervisor who drove us engineering types nutty, by saying things like "you just can't measure that in metric". :rolleyes:

Evan
05-10-2007, 08:20 AM
A profound irony in all this is that the King of all things Chinese, Harbor Freight doesn't sell metric screws ! Check out their hardware assortments sometime....they have a few metric things, like metric O ring sets...but no metric bolts, cap screws, nuts, etc

We have a major retailer in Canada called Canadian Tire. They are a major vendor of auto parts and many other home and garden items, especially tools and hardware. In the aisle where all the ridiculously expensive little blister packs of SAE screws, nuts and bolts are sold is a sliding rack with many little drawers at the far end. It is filled with a wide assortment of bulk metric fasteners including every type of screw, cap screw, nut and bolt. Pick your own quantity, put in plastic bag and label with SKU and pay for them.

Lew Hartswick
05-10-2007, 08:37 AM
BigBoy1 said: Quickly calcuate the number of inches in a statue mile.

And just WHY would anyone want to know that? :-)
...lew...

Swarf&Sparks
05-10-2007, 08:48 AM
Murphy's law, corollary 33.68.03 (revised 10-04-2006)

Any measurement in a document or drawing, will be expressed in the most obscure units available:
EG, velocity of rifle projectiles will be expressed in furlongs per fortnight

Tolerances of any critical component will be expressed in non-native units:
EG in a metric drawing of an M6 SHCS, tolerances will be specified in micro-leagues :(

BigBoy1
05-11-2007, 05:29 PM
Are we talking units such as, Furloughs per Fortnight???

Bill