Metric or Imperial

[Jasonb]

Mike, as you know I'm a UK woodworker but I tend to use imperial for model engineering, the main reason being that all the models I have made are drawn in imperial and this is the case with at least 95% of whats available. Also most of the materials sold in small lengths by the Mod Eng trade are imperial although both metric and imperial tooling is easily available.

Both my lathe and mill have imperial hand wheels but as the mill has digital scales fitted its just a case of pressing a button to go from metric to imperial.

If you use digital measuring equipment then it makes little difference what your machines are calibrated in and with the low cost of reasonable digi micrometers and callipers that would be the best option.

And if you have difficulties working in 1/16ths, 32nds and 64ths you can always convert to decimals of an inch and get the calculator out

Jason

 

[rickharris]

John said- "UK can understand both"

Can anyone understand this metric system??
am I missing something?? it's a six inch ss that i have had for years.

Well perhaps this will help - or perhaps not:

1 ft = 12 inches = 72 picas
1 in = 6 picas = 72 points
1 pica = 12 points

Its a print measurement as said.

 

[13AL]

Well first off I need to apologise to MattMoore whom originally started this thread. I was politely informed that what I have done is called "thread hijacking"?? I have strayed from the original topic, newbie mistake :-[

But....I am still curious about this ruler and may continue this in a more appropriate manner!

13AL

 

[Loose nut]

In Canada we are "officially" metric, in reality outside government organizations and science we are mostly still Imperial. Most tools are imperial and finding a metric tape measure can be an adventure. I work in an oil refinery and everything is still done in imperial with no change in site. I personally refuse to go metric, I don't like it when the government tries to shove something down our throat and getting Imperial tools and supplies here will not be a problem in my lifetime.

If your into Model engineering, Imperial may be a choice because it will keep you closer to the original equipment, 55 degree threads and all, as long as you can get tools to support what you like to do.

As for which is better, I once had a snotty collage kid tell me I had to go metric,this was at a show our ME club put on, I said "why" to which he replied it was better because it didn't use fractions (which is false, metric can use fractions it usually just doesn't) . At that I told him I don't use fractions I use the inch divided into thousands and the MM divided into hundreds is no more accurate, they are both decimal systems at that point and if we don't want to use fractions for tooling they all have decimal equivalents, it's just easier for us old fogies to use what we were trained on.

He couldn't come up with a reply and just turned and walked off. Don't believe all the propaganda that people want you to believe, Just do what you want and what is best for you. Since Britain has succumbed to the French disease (metric system) that might be a better choice.

 

[AlanHaisley]

I think that when most people argue metric vs imperial what they are really arguing is decimals vs fractions.

Henry Ford pretty much negated that by promoting decimal inches.

Except in physics and chemistry, little is gained taking metric before decimal imperial. Even there, the formulas can become elaborate enough that it's not clear why one set of constants of proportionality has much merit over the other.

That said, most things that people model in metal seem to be old machines, motors, or engines which were primarily built to imperial dimensions.

 

[mklotz]

Where most of the old Imperial luddites run aground is on the idea that the only advantage of metric is its use of base 10 units.

What they overlook is the fact that metric is a thought-out SYSTEM and not some hodgepodge of tradesmen's units of convenience.

When you design a linear measure, for example drill sizes, you want the designation open at both ends so that if drills smaller or larger than the initial complement can be added without complexity or confusion. You also want the designation to convey information - in this case about size. Designating drills with letters or numbers defies both these rules. So do sheet metal gages that tell you how often it's been through the rolling mill but gives no indication of thickness. With Imperial one ends up with such idiocies as 00-90 screws.

You also want the linear measures to relate simply to the area and volume measures. 1000 cc is a liter but a quart doesn't relate simply to cubic inches, or decibushels for that matter.

Most of the common liquids dealt with are water based so it makes sense for the volume measures to relate directly to water weight. A liter of water weighs a kilogram. Only god knows what a quart of water weighs in pounds - a pint's a pound sort of works here in the US but our pint isn't the same as a British pint. Neither is our barrel. There's nothing more nonsensical than two units with the same name and differing values but Imperial has them in spades.

And then there's the idiocy of using the same unit, pound, for both mass and force - a fact that means that almost no American can compute an acceleration and get it right the first time out.

The vast majority of people are borderline innumerate - they have serious difficulty making even abstract (non-dimensioned) computations (ask any high school senior to add two improper fractions if you don't believe me). So, in the interest of more airplanes crashed because the fuel load was calculated in kilograms but dispensed in pounds, we saddle them with a system so stupid it defies description.

Now, ask me what I REALLY think of the Imperial system. :wall:

 

[rake60]

Oh I don't think it's all that ludicrous Marv.

I'm drawing up a plan for a display stand to mount a few of my engines on.
The dimensions are totally Imperial!
I thought I'd make it a cubit long, a hand wide and two digits high.

I've used metric micrometers.
Two full rotations of the thimble = 1mm
Two full rotations of the thimble on an Imperial mic = .050"
That works out to being about .012" less than 1/16" which in the closest
nominal fraction.....

OK Maybe it IS that ludicrous!

Rick

 

[Loose nut]

Technically there no longer is a metric system it's now the SI or international system. Before this there were many metric systems in place and while they may all have used the MM as a standard measure the taps, dies and drills along with other things were frequently different county to country, this is one of the reasons for the SI version of metric. That being said one of the most common complaints you hear is that there isn't a drill, tap etc. that is close enough to my needs (compared to the old metric or imperial), so the continuation of the imperial system and many of the old metric thread sizes. Another complaint is the the CM should have been used instead of the MM it's to small (several European country only use the CM IE: Germany)
The imperial system was rationalized out of centuries of experience into it's modern form not laid down by a bunch of bureaucrats who didn't ask anyone what they wanted it to be, and it really doesn't matter if the thread is a 00-90 or 1/4" or M4 by 1 you just get out the bit the the plans call for and use it, you don't have to know the double depth or pitch to make it work. They are both decimal systems (for our purpose anyway) and neither has a real advantage in the home shop.

While the SI might make more sense for people just learning today, for people brought up on Imperial it is bloody miserable it fathom.
Use the system that you want, as long as you can get the tools anyway.

Now that I have shown the inherent superiority of the Imperial system over the SI system the most compelling reason to use the Imperial system is that SI uses commas as separators, there call decimal POINTS not decimal commas, that in it's self is reason enough to abandon the metric system.

I DON'T DO METRIC.

 

[Bogstandard]

Please gents, before you go any further with this argument, could you please go to the first post on this topic and read what it is about.

John

 

[Loose nut]

Killjoy!

 

[Bogstandard]

LN,

not a killjoy at all.

how would you like to ask a question, and it ended up too complicated or way off subject.

i am not an administrator, so have no say in it, but it is pure courtesy to respect the original question being asked.

if you want to go into such detail, i am sure you are capable of opening your own topic on the subject, where like minded people could discuss away to their hearts content.

john

 

[Loose nut]

Bog, if you read the posts I put in, the gist of it was that Matt should do what he wants and not to be influenced by what other people (in his country) want or think he should do. It really doesn't matter which system he uses as long as it suits him and he can get the tools he needs. Just because he lives in a Metric country he doesn't have to go metric. What people do in there home shops is one of the last places people still have free choice.

I also had to take a somewhat humorous shot a Marv,s metric is perfect thread, he waved the red flag and I supplied the bull.

 

[mklotz]

I also had to take a somewhat humorous shot a Marv,s metric is perfect thread, he waved the red flag and I supplied the bull.

You did indeed.

 

[Tin Falcon]

Hmm this thread is getting interesting.
I think choosing the measurement standard in the home shop is akin to what lathe is best for me to buy. A personal choice.
Saying I like metric because or I like imperial because is fine as long as this does not get into a argument or debate. all here are entitled to opinions and can freely and respectfully express them. We did give Matt a lot to think about.
Like I said before in other posts for those that want to use imperial drawings in a metric shop just let 1mm =1/32 of an inch this will scale down the model 20% but will result in even metric numbers rather than odd ball sizes.
Tin

 

[AlanHaisley]

It depends:

On what you own.
On what you can easily buy.
On what you are comfortable with.
On what you intend to make and where the plans come from.
Perhaps especially on the availability of fasteners, fittings, bearings, etc. that you intend to use.

Certainly if you are making a part and it will be measured in metric units, the only importance that the original dimensions have is in the amount of waste that will be produced in making the part. (Assuming you have the necessary metric tools.) The same goes, of course, for making it to an imperial measurement.

If you are converting an imperial design to a metric design, a straight numeric conversion doesn't make sense. There won't be any standard metric fittings and fasteners that work in that case.

I think that what it gets back to is after considering the tools and instruments you own, the most important factor is to decide just what you intend to make.

The easiest choice would come if your intent was to make own designs and inventions, totally unrelated to the availability of plans, kits, and castings on the market.

Alan

 

[MattMoore]

Thanks for all the input, I was expecting it to open a small can of worms, but not one this big ;D
As of yet I don't own any machinery or tools. I'm starting from a blank page.
I have a few tools that could be carried over from my day job. But I would just prefer to have new everything.
No second hand old iron machinery, for now
One of the things that prompted me to ask was from one of the books I have read training for my day job.
It said that 0.1mm was very close to 0.004", I knew that working to 4 thou wouldn't be nearly accurate enough.
It never occurred to me for some reason that metric could be taken to a second decimal place.
I think based upon that I'm going to stick with metric, from my rough calculations, one thou would be equal to about 0.025mm
If i shoot for 0.01mm then I can't be going too far wrong.
Now to start buying ;D

 

[Julian]

Matt,
I've bought Asian Metric machines and now a 40 year old imperial lathe. I prefer metric to imperial any day as its what I have learned and used for years. Two decimals of metric is mostly accurate enough but if you make two parts to fit together make them fit by trying them not by dead measurement. I agree the only time you will have problems is when plans come imperial but you can soon convert with a computer and Excell or any free conversion program. Metal stock is mostly metric with imperial equivilent. If its wrong machine a little off then you know its the right size. I've got some lengths of bar listed at 8mm. Only about 1 in ten are actually 8mm dead-on!!!

I am a great believer in "suck it and see" so just go for it. work to the measurement you need not what they say you should.


Julian

 

[Bogstandard]

Matt,

I think you will find that metric machines aren't marked up in 0.01mm but in 0.02mm (roughly equal but slightly smaller than 1 thou). So really there is very little to choose between each.

The choice has to be yours and yours alone, you will be the person using it. The kind people on here have given you a lot to think about, and you are doing it the right way, trying to get it right first time.

John

 

[mklotz]

"You could also say that Imperial is more accurate..."

Please, John, rephrase that. There's already so much rampant misunderstanding of measurement systems demonstrated here and such statements simply add to the confusion.

It makes no sense at all to talk about the accuracy of a measurement system. Any system can be subdivided to any level of precision. Accuracy is something determined by the tools used, not the units in which they measure. I'm sure that you understand this, John but it's obvious from previous posts in this thread that many folks do not understand that accuracy is in no way related to the measurement system used.

 

[Bogstandard]

Marv,

Thanks.

Done.

John.