# Metric or Imperial



## MattMoore (Mar 30, 2008)

Hi all,
I'm in the process of setting up a workshop at home for engineering.
These engines I keep seeing posted are really getting me excited about working metal.
I'm a joiner by trade and work in metric, albeit to 0.5mm tolerances most of the time,
Not quite engineering standards. Although my Dad was a trained pattern maker, but thats another story.
I'm assuming that the majority of people here stick to one unit of measure.
But I see a lot more imperial than metric.
I'd like to try and stick to metric for making the engines and some tooling I need at work.
Will I encounter any problems sourcing material and hardware in metric?
Or should I try and get my head round imperial?
I only really want to buy one set of measuring tools, and tooling so your comments will be greatly received.

Thanks

Matt


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## bentprop (Mar 30, 2008)

Hi Matt.I would say it depends on your location.In the UK,Europe or Australasia,metric is the standard,whereas in the USA,imperial or US standards are used.
Suppliers stock both,but in the US standard is probably cheaper,everywhere else,metric is cheaper,and easier to get.
If your confident with metric,stick with that.Personally ,I find metric the easiest,because that is what I was brought up on.
Welcome to this great hobby,and whatever form it takes,enjoy it!
Hans(New Zealand)


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## mklotz (Mar 30, 2008)

You'll get more meaningful answers if you put at least some hint of your location in your profile.

I'm an American living in America and my recommendation is that you use metric unless you happen to be modeling in the USA. Here Imperial tools and parts are cheaper and more easily available so going Imperial is an option to consider. Otherwise, the Imperial system is a complete nightmare - both directly for its idiot units and indirectly for its absence of any sensible standards. If metric is a tenable option economically in your location, use it and revel in the fact that you can.


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## rake60 (Mar 30, 2008)

Hello Matt

Your introduction post did say you were from the UK.
That being the case, I would stay metric.

Where I work we get prints in both Imperial and Metric dimensions.
Our measuring devises are all Imperial, but dividing a metric size
by 25.5 doesn't seem to be too overwhelming for anyone there. 

In my home shop all my model work is in Imperial sizes except for
the small threads. The local hobby shop only had a Metric Mini
Tap and Die set in stock the day I decided I need one. That too 
is no problem since the area hardware stores stock all the small
metric size screws, bolts and nuts.

Rick


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## MattMoore (Mar 30, 2008)

Thanks for the replies so far,
I am based in the UK (i've updated my profile now)
It's only from my reading material that I have assumed the majority of things to be done in imperial, 
But I think thats mainly down to alot of the writer being trained before decimalization.
I'm going to be purchasing asian machines when I get round to that, am I right in understanding that
on the imperial machines they sell, the lead screw is still a metric one?

Thanks


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## Tin Falcon (Mar 30, 2008)

kinda like the others said
Location Location Location!!
What is the prevailing standard in your area. 
Most US catalogs have a limited supply of metric sized materials drill rod etc. Maryland metrics is an industrial supply house that specializes in metric tools hardware and materials. mdmetric.comlocated on the edge of Baltimore MD
The other challenge in the US may be finding a lathe and mill with metric dials and threads. Although I did come across a NOS small metric lathe on e-bay that I set up for a friend(No motor or tooling) Edestal brand IIRC. 
Harbor freight and others have electronic digital calipers that switch from inches to mm with the push of a button . But finding metric micrometers in the US may be harder. 
I remember the big push in High school that the US was going metric within ten years , that was almost 30 years ago. 
so browse the industrial supply catalogs to see what is available. 
hope this helps 
Tin


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## Lew Hartswick (Mar 30, 2008)

rake60  said:
			
		

> Where I work we get prints in both Imperial and Metric dimensions.
> Our measuring devises are all Imperial, but dividing a metric size
> by 25.5 doesn't seem to be too overwhelming for anyone there.
> Rick


I hope you don't use 25.5 at work Rick. 
  ...lew...


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## zeusrekning (Mar 30, 2008)

Yeah Rick I'd like to talk to your quality control guys. :big:


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## rake60 (Mar 30, 2008)

Alright, would you believe 25.4??? LOL

I'm a machinst, what more can I say? 
Actually I multiply the metric size by .03937
To convert an Imperial size to Metric I multiply by 25.4

I HAVE done that wrong in the past.
Looked at the part and thought, "That ain't right!" 

Rick


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## bob ward (Mar 30, 2008)

If you are of average intelligence stick with metric. 

Imperial is only for clever people who can do fractions and can divide stuff by 16 32 and 64


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## tattoomike68 (Mar 31, 2008)

One unit or the other means nothing to me unless you are talking threads. metric bolts cost more here, same with taps. other than the cost factor it means nothing to me, a number is a number.

I have made all kinds of stuff over the years and the units was never an issue, I just made the parts.


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## DickDastardly40 (Mar 31, 2008)

Matt,

I think it depends on what you want to make and how you prefer to make it. 

For instance, I'm making a triple engine from scratch, the plans are imperial, therefore that's what I'm working in for this project. If you don't mind making it up as you progress a la Bogstandard or to suit what tooling you already have then whatever you are most comfortable in may suit. If you are intending to build from a kit then what the native code of that will be your default.

Which machinery you buy or have access to may have a bearing on what it easiest to produce. It is awkward (not difficult) to cut a imperial thread on a metric lathe (or vice versa). Try not to mix metric and imperial on the same job (not always possible). As regards measuring tools an inexpensive digital caliper is an easy method to switch between the two. I have a 6" steel rule I always double check larger sizes with as it does both without having to press a button.

I don't find that one code is more expensive than another in the UK, though getting esoteric premade fastenings may be more difficult.

Hope this has helped.


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## compound driver 2 (Mar 31, 2008)

Hi
All my working life I have used imperial, Some £40,000 in tools are all imperial. I think il stick with imperial its easier to use and makes a lot more sense given that I work on 100 year old designs.

If your even half comfortable with a system stick with it but be prepared to convert a lot of the decent drawings from imperial to metric.

Cheers Kevin


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## gilessim (Mar 31, 2008)

Hi Matt, I'm also a woodworker by trade (and English but 15 years in Italy) at school we still used imperial but soon had to change to metric. For staircases and stuff I use both with the metric and inches tape measure, maybe only found in the UK!, using which was nearest! (laziness!) now, for engine work, I printed up some tables ,decimal and fractional imperial to metric and stuck them on the wall to help me with the over the pond plans.

I wouldn't worry to much about stock sizes being metric if you're making something with imperial dimensions as it will only help you to be more precise with your machining!, the only problem I've found really is with drill sizes and reamers but you can get easily drill bits in 10ths of a mm (also in 100ths if you're lucky and rich!), reamers and laps, you can make yourself to take of a few 100ths if you need to and I'm sure I don't need to tell you to adapt, using the kit that you have if you can, rather than spending 20 quid on a reamer ,or something, that you may never use again!

Thread sizes, as DD says, can be a pain but BA or metric you can easily get there and they're close enough to the american sizes to not create too many problems!

One thing I find very useful is the number drills, I got mine in the UK, together with yet another conversion table stuck on the wall, for small stuff, there is nearly always one very close to the size you need, metric or imperial.

Hope you get my drift and that this helps you! ,lots of cleverer guys than me on this site BTW!

Giles


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## SignalFailure (Mar 31, 2008)

Hi Matt

As another relative newcomer from the UK I decided to go metric although being almost 50 by nature I think of most stuff in imperial. My vernier/lathe/rules have both units only my drills and taps and dies are uniquely metric.

For me their are two downsides to metric:

1 Many materials are still only sold in imperial sizes (at least at my prefered supplier) so you almost always have to at least skim some metal before starting any real work. For example if the plans call for an accurate 3mm dia rod you might have to use a 1/8 and lose 0.175mm. This situation is set to improve I'm told but we have been officially metric for ages so don't hold your breath!

2 The vast majority or plans (free or otherwise) are in imperial and therefore require conversion which for a newbie considerably increases the likelihood of mistakes. That said, the conversion process does make you think about the model in great detail at the outset! For the uber-simple engines I've made there haven't been any major issues but I wouldn't fancy tackling a locomotive or traction engine with only imperial drawings!

If I had to start over I think I'd probably go for imperial - I'm just as comfortable with the units and both the above issues would disappear. Thinking about it I haven't got that much invested in taps/dies/drill so I might just go 'old money' anyway!


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## compound driver 2 (Mar 31, 2008)

HI
One other point in passing. metric threads just never look scale nor do the bolt head or nuts. 
At least with BA (ok BA is a metric derivation) theres a fighting chance of getting a scale looking fitting. Same with the model engineer thread sizes both 40tpi and 32 tpi. These if your really seriouse can represent a lot of old English threads at scales like 1 inch to the foot and 2 inch to the foot.

Cheers Kevin


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## Bogstandard (Mar 31, 2008)

Bob said.



> If you are of average intelligence stick with metric.
> 
> Imperial is only for clever people who can do fractions and can divide stuff by 16 32 and 64



That is why we gave it to you colonials in the first place. We knew in the future you would stick with it because you couldn't come up with your own standards. Look at you now, US still in the dark ages, and making for your own market, the rest of the world in a shining standard light. UK can understand both.

But joking aside, if you are happy with metric, stick with it, and understand imperial when it hits you. You will find after a time, working in both comes naturally.

A digital micrometer and vernier, plus a thread and size conversion chart, will basically be all you will need to get started.

John


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## gilessim (Mar 31, 2008)

Well I think this says it all


> One unit or the other means nothing to me unless you are talking threads. metric bolts cost more here, same with taps. other than the cost factor it means nothing to me, a number is a number


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## 13AL (Mar 31, 2008)

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.


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## SignalFailure (Mar 31, 2008)

Guess: is it something to do with typesetting (points)?


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## Jasonb (Mar 31, 2008)

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


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## rickharris (Mar 31, 2008)

13AL  said:
			
		

> 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.


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## 13AL (Mar 31, 2008)

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


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## Loose nut (Mar 31, 2008)

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.


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## AlanHaisley (Apr 1, 2008)

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.


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## mklotz (Apr 1, 2008)

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:


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## rake60 (Apr 1, 2008)

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


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## Loose nut (Apr 2, 2008)

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.


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## Bogstandard (Apr 2, 2008)

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


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## Loose nut (Apr 4, 2008)

Killjoy!


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## Bogstandard (Apr 4, 2008)

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


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## Loose nut (Apr 4, 2008)

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.


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## mklotz (Apr 5, 2008)

Loose nut  said:
			
		

> 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.


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## Tin Falcon (Apr 5, 2008)

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


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## AlanHaisley (Apr 5, 2008)

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


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## MattMoore (Apr 6, 2008)

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


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## Julian (Apr 21, 2008)

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


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## Bogstandard (Apr 21, 2008)

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


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## mklotz (Apr 21, 2008)

"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.


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## Bogstandard (Apr 21, 2008)

Marv,

Thanks.

Done.

John.


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## tmuir (Apr 21, 2008)

I'm pretty much a newbie myself and still kitting out my workshop.
My personal preference is metric as that is what I was brought up with and was planning on going completely metric in my workshop but I've already hit snags with this idea.
First of all I'm finding it really hard to get material in metric sizes without paying a fortune for it over about 4mm.
Secondly to ease myself into using my lathe I'm restoring a number of old engines I've got which are of course all pre-decimal so I need imperial taps / dies and bar stock for them and also I would say about 80% of all my plans are in imperial.

I guess what I'm saying is my preference is for metric but the reality is I need to work in imperial for atleast a large part of what I do.

In the future when I scratch build I plan to make all my measurements in metric but will probably end up using imperial bar stock as its a lot cheaper.

I live in Perth Western Australia and before I started looking for material I just assumed metric would be easy to get as we changed over to metric over 40 years ago but atleast where I live metric bar stock is not readily available in small quanties for reasonable prices.


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## Loose nut (Apr 23, 2008)

I got this link off of the HSM form, they are also talking about this topic, it has an interesting point of view.

http://briontoss.com/education/archive/miscjuly00.htm


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## IanN (Apr 25, 2008)

Hi,

I'm still trying to work out whether the website above is intended as humour or whether the author is trying to make a genuine point.

There are so many factual errors, misleading non-truths and unsupported bias opinions in the article that it is hard to take it seriously.

I wonder what the author would make of our branch of engineering where the use of metric inch divisions (thous) are the norm when dealing with precision Imperial measurements?

Ian.


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## tmuir (Apr 25, 2008)

Slightly off topic but I collect model live steam locos and my fav size is 16mm.
which is 16mm to the foot scale.
I just love that one, who was the crazy gut that came up with that. :big:


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## CrewCab (Apr 25, 2008)

tmuir  said:
			
		

> 16mm to the foot scale.


Mmmmmmmm ............. got to say I can't quite follow the logic either ??? : ;D ............. but .... wth .......... it works 

As for Metric versus Imperial, I was "dragged" up with both ....  .... at school it was all Imperial, when I started work as a Draughtsman (in 1968)  the drawing office worked in Imperial, but at college for the next 4 years it was Metric, consequently I had to understand both, and now I can happily work with either ........... but .......... I still think in Imperial 

Dave


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## alan2525 (Apr 25, 2008)

16mm:ft scale is based on using O Gauge (1:43.5) Track 32mm to represent a scale 2ft gauge.

That's the problem with model railways as each scale requires it's own track to run it on. Take OO scale for example - 4mm:ft but running on 16.5mm track which is out of scale for the real 4ft 8 1/2"

I use metric, my lathe is US so calibrated in Imperial, I use a metric dial gauge to work around that. Although when I have to do any large building jobs I always use Imperial as the rule has bigger numbers and am less likely to mess up by 100mm!

As far as the Imperial system goes though, I can never work out why anyone would want to decipher fractional sizes on a drill bit, what kind of measurement is 51/64ths? Metric all the way for it's sheer simplicity!


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