Can a metric baby do imperial?

[beeza650Participant @beeza650]

I’m kitting myself out from nothing and need to do it on a tight budget. Most of the used metrology equipment I see is imperial. I’ve seen quite a good set, for what seems like a very fair price but don’t want to jump in and regret it later.

The question is, my mind works in metric through and through, am I going to forever rue the day I bought imperial measuring tools….should I hold out for metric or does it cease to be an issue after a while (or is a non-issue in the first place?)

Thanks Oliver

[JasonBModerator @jasonb]

It is simpler, quicker and less error prone to do metric work with metric equipment.

To some extent it will also depend on what sort of work you want to do. If just general machining of bits for yourself then metric would be the best option. If you want to make models to ancient imperial designs then you may well be better off working in imperial so the imperial equipment will be your better bet.

Buying new equipment may well be a digital calliper rather than vernier in which case the digi can be switched between the two though you still need to do any conversion calculations correctly. New metric may also be cheaper and as good as second hand imperial where you may be paying  a premium for a brand name.

[Andrew CrowParticipant @andrewcrow91475]

Hello Oliver, your Avatar would suggest that you have an interest in old British motor cycles, in which case everything would have been made to imperial standards so if you intend to make parts for those, then buying imperial metrology would be OK.

However, if you’re not going to produce parts in imperial sizes then I would follow Jason’s advice.

Andy

[SillyOldDufferModerator @sillyoldduffer]

The advantage of metric is it does away with the blizzard of unnecessary conversions built into Imperial measure.  It makes no sense to me to mix metric and imperial because that adds another layer of error prone maths.  (And I’m terrible with sums!)

I decided 12 years ago that my workshop would be metric, only doing Imperial as a special case.   Being given a fully equipped Imperial workshop, or specialising in building choo choos from old plans, or restoring old equipment, being unfamiliar with metric, or being American are good reasons for going Imperial, otherwise not smart in 2025!  Pure metric simplifies CAD, measurements and buying fasteners and tooling etc. If you’re already metric, don’t muddy the waters with another system, especially one that’s slowly disappearing.

I’m wary of buying second-hand metrology because whether it’s any good or not depends on condition. and that depends on the item’s unknown history.   If accuracy was important I’d rather buy a set of new metric slip gauges rather than rely on an ancient imperial set that might be worn, or polished up to look good.

Actually, measured accuracy isn’t a high requirement in my workshop.  Digital calipers are generally ‘good-enough’, in the ±0.02 region and I rarely use a micrometer.   Reason is I use an old-school technique called fitting, in which parts are gauged by each other, not measuring at all.   When fitting a shaft to a hole, I don’t accurately measure the hole and then accurately measure a shaft to fit,  instead I turn the shaft slightly oversize and then trim it down to fit.  Ordinary spring calipers are used to judge fit when parts can’t be tested directly.

High end metrology is essential when producing exchangeable parts, and in the past accurate tools and jigs were a good way of sacking thousands of expensive skilled workers!  Neither applies to my hobby work, so my metrology is lightweight and informal.

Unless there’s a strong need for accuracy, being on a tight budget suggests money would be better spent on tools and materials, with metrology well down the list. A digital caliper does Imperial and Metric, as do DROs, so there may be no need for much else.

Dave

 

 

 

[John HaineParticipant @johnhaine32865]

Go metric, no contest!  There’s one thing you need to remember – since I think 1959 one inch is defined as exactly 25.4 millimetres.  With that and a calculator you can cobvert either way with ease.  After a bit you’ll find that other imperial measurements metric equivalents stick in your mind too.

[beeza650Participant @beeza650]

Wow some excellent advice there.

@Dave – you’re absolutely right, I very much doubt I’ll be making many things to an imperial spec. I intend to do mostly repair work so I’ll just be to “fixed” spec 🙂 …or if I’m going to invent something then I’d just do all that in metric. The only reason I was putting metrology first is because a rather nice imperial bundle came up for £240 which would be a heck of a lot more to buy individually. The guy’s gone silent – so it may have gone now though.

@Andy – yes I do plan to work on old bikes – and newer ones or ones from Europe probably in equal measure so rock and hard place on that one.

@Jason – I have a digital vernier and micrometer (quite a small one). They’ll be great for precision but I’m getting very peed off with flat batteries so want manual equivalents. Plus I need dial gauges and more….

I’ll need to be honest with myself – I’m going to make mistakes – having to contend with imperial on top that is probably just making life hard for myself.

Time to start searching German Facebook and eBay for metric bundles 🙂

[Andrew TinsleyParticipant @andrewtinsley63637]

I work on both old and new items, I have no problems using metric or imperial units and have tooling and measurement kit in both systems. I have never had a problem with converting from one system to another. This is probably to do with my age. I learnt in imperial units and then was forced to use CGS units when I became a physicist (CGS has transformed into MKS et al since).

If you have to use one or other system, choose the one you are comfortable with, end of story. I find that good second hand imperial tooling and measuring kit, is considerably cheaper than new or second hand metric equivalents despite the claims to the contrary

Andrew..

[Speedy Builder5Participant @speedybuilder5]

But even imperial has its querquiness .  Will you work in fractions or decimal inches. My metric analogue vernier calipers have both metric and fraction scales, the fraction is to the nearest 1/128″.  Cheap digital callipers can have metric, decimal and fractional inch selectable readings.

Bob

[Howard LewisParticipant @howardlewis46836]

As already said, in our environment, no matter how good our measuring equipment, we are unlikely to be able to work to industrial standards of precision.

And we are discussing UNITS of measurement. It will not change the part whether we measure it as 1/4″ or 6.354 mm.

My advice would be;

If the component needs to be made to a Metric dimension, measure in mm; if it is Imperial, measure in Imperial.

M6 is 6 mm  x 1 mm, not 0.236220472 x 0.039370078″, any more than a 1/4 BSW thread is 6.354 x 1.27 mm

But a calculator can be useful, at times.

Horses for Courses!

Howard

[Nick WheelerParticipant @nickwheeler]

I think you should consider what you actually need rather than want. You can spend a lot more money/time acquiring and storing somebody else’s list of essential tools that you never use.

Some of my examples:

1-2-3 blocks. I use one for squaring the lathe tool post to the chuck, but they’ve never been of any use on the mill.

Soon after getting the lathe I bought a budget set of 0 – 100mm micrometers in a nice wooden box. The 25mm is kept next to a 1″ equivalent***, the 50 is used occasionally, a friend borrowed the 75 for one job and the 100 has never been out of the box. I’ve had them over twenty years…

Dial and test indicators. I have both. Metric and imperial dials. And a couple of stands. Rarely use the dials, and hardly ever the tests. And they’re comparative tools, so it doesn’t make much difference what they’re calibrated in.

 

Also, why are you insisting on used? While we would like to think that all expensive measuring tools live in jewellery boxes when not being used with care by highly trained artisans, that has to be the exception to the rule. £240 at some where like Arc will be more than enough to get you started so you can figure out what you need. Most of my work is measured with a digital caliper.

 

*** I have 1″ and 25mm micrometers so I don’t have to convert. Doing that takes time and gives another chance to make mistakes.

[peak4Participant @peak4]

Just a few observations, not suggestions as to which are the “best” units of measurement.

Re Calipers, I’m forever changing batteries in Lidl/Aldi cheapo ones; I but them in quantity (from Lidl or eBay) and it doesn’t bother me too much if I’m using the workshop frequently, but a pain with items I rarely use and are flat when I pick them up.
I store those with the batteries out, for such as angle gauges, it also save them corroding inside.
I can’t remember the last time I changed a battery in either of my second hand Mitutoyo calipers, and they use the same batteries.
The above applies to cheap versus expensive digital micrometers too.

Too much danger of mis-entering numbers in a calculator, so I often use a digital caliper as a unit converter (or Zeus tables).
This applies particularly for someone who doesn’t have a “feeling” for both measuring systems, where a discrepancy might be more obvious; i.e. mis-thinking ten thou for a tenth of a mm when tired.

Do you already have machine tools such as a lathe or milling machine; absent DROs (which I don’t have) it probably makes sense to have measuring gear in the same units as your machines.

For use in a home workshop, we don’t really need fully NAMAS calibrated equipment; consistency is more important between all instruments and machines, so that your 0-1″ micrometer, reads the same as your 1-2″, the same as your bore gauge, and caliper(s) etc.

High quality bearings are made to tight tolerances, and can serve, with care, as slip gauges to compare instruments.
Speak nicely to a local bearing supplier and try and pick up some loose bearings of known sizes, ball or roller.
Two of each makes calculations easier when used for measuring dovetails etc.
They can even be used to ensure the anvils of a second hand micrometer are actually parallel at various measurements, thus indicating if the instrument has previously been dropped.

Because my first larger lathe was an imperial Myford, along with my micrometers, I still tend to think and work in imperial, but readily also use Metric on my larger lathe with has dual dials; it doesn’t take long to get used to it, and having dual dials also give one a better feeling for the two systems alongside one another.

Despite working in imperial, for many years, almost all of my drill bits were metric in 0.1mm steps from 1-10mm

Bill

 

[duncan webster 1Participant @duncanwebster1]

Where did 6.354 come from? 25.4/4 is 6.35 exactly

[duncan webster 1]

On duncan webster 1 Said:

Where did 6.354 come from? 25.4/4 is 6.35 exactly

Well I did mention errors in the first line of my reply😉

[larry phelan 1Participant @larryphelan1]

I think the late respected Harold Hall answered that one long ago when giving advice about setting up a workshop. He advised to go Metric from day one, pointing out that the Imperial system simply jumped from one value to another with no logical connection between them. My generation was brought up using the old system, but when we decided to go Metric, it happened overnight. We finished work one Friday, using Imperial, and on Monday morning we were issued with Metric drawings, simple as that !

Took a bit of getting used to for some guys, but it makes a lot more sense, no more jumping from 12 to 3 to 5 1/2, inches, feet perches ect.

Should have been done years ago, so I would say, forget the junk, go Metric.

[duncan webster 1Participant @duncanwebster1]

Why do you need a ‘bundle’? I made 2 locos with only a 0-1″ mic, a couple of rulers and a digital caliper, which would cost a lot less than £240 new. Having now gone metric I’ve bought a 0-25mm mic as well,and I’ve been given 25-50 and 50-75, but I hardly ever use the last 2.

[duncan webster 1]

On duncan webster 1 Said:

Why do you need a ‘bundle’? I made 2 locos with only a 0-1″ mic, a couple of rulers and a digital caliper, which would cost a lot less than £240 new. Having now gone metric I’ve bought a 0-25mm mic as well,and I’ve been given 25-50 and 50-75, but I hardly ever use the last 2.

Exactly.

Although a way of measuring bores would be handy. £20 for a set of telescoping gauges.

[peak4Participant @peak4]

Purely out of interest, I’m not suggesting Oliver seeks out either of these instruments, a couple of micrometers for those who desire metric and imperial on the same one.
Digital electronics have revolutionised the concept.

First is a rather grubby Mitutoyo Metrinch.
This has an imperial thimble marked to tenths, but a metric numeric display.
I do use it if I’m making something to metric dimensions on my imperial Myford, but mainly as a double check of my own maths.
As well as imperial-metric, they also come as metric-imperial, as well as all imperial or all metric.
The tenths vernier looks off slightly, but it’s parallax error in the photo; it’s pretty much spot on.

Then we have the slightly weird Shardlow Anglometric.
As far as I know, these only worth this way around; no idea what sizes were made, but I have 0-1″ & 1-2″.
The first thing to spot, is the spindle thread isn’t 40tpi, and needs 5 full turns rather than 4 to complete 1/10″; that had me fooled when I first used it.
I’m assuming this is to allow room for the scrolling red scale for metric use.
Again, slight parallax error on the thimble vernier.

Turning it over gets more interesting; you really do need to think about where you put the decimal point in your additions.
For metric, use the red scale(s).

We have 12.5mm + 0.20 on the red thimble scale to give the final 12.7mm

I think I understand why they weren’t that popular, and fell out of production.

Bill

[Mark EasingwoodParticipant @markeasingwood33578]

I received an email from Machine DRO earlier, they are having a Mitutoyo sale.

150mm/6in digital calipers are £80 + Vat, usually £140 + Vat, so a bit of a bargain.

As an aside there is supposedly a lot of fake Mitutoyo stuff for sale on the web.

Click HERE for link.

Mark.

[bernard towersParticipant @bernardtowers37738]

their only a bargain if you need one.

[NealebParticipant @nealeb]

With one real exception, I don’t find switching between metric and imperial units to be a big issue. The exception is that I still can’t get used to putting on an appropriate depth of cut in decimal fractions of a millimetre – DoC is still in thou to my simple mind, although I am slowly, ever so slowly, getting the hang of it!

What I do find complicated if not somewhat confusing is the wider picture. I’m currently redrawing my Don Young Black 5 from DY’s original drawings to a Solid Edge 3D model. Virtually all the dimensions on the original drawings are imperial, and pretty much all fractional rather than decimal. That’s OK – I type in dimensions, in fractional inches, when creating my model and the software just translates them into metric, as many of the components will end up as a toolpath for CNC machining and my mill speaks metric only. No problems there. But I’m currently looking at a brass spacer plate that sits between cylinder and frame. So, its thickness is potentially significant in terms of the valve gear, connecting rod, etc, alignment. The drawing gives the thickness as 5mm. Why? Did DY find that 3/16″, a very near equivalent (about 4.7mm), was not on the market back when he drew this? I find that after a quick look, I can actually buy 3/16″ for less than 5mm, which I found surprising – but if I order 3/16″ am I actually likely to receive 5mm as the near equivalent? Do I order 6mm and machine it down, just to make sure, but at greater cost and time? Does the nominal 0.3mm actually matter anyway – which I what I shall be examining on the drawings later?

A few years back, when I was building my CNC router, I designed in 50x12mm aluminium spacers at one point – I was sure that metric sizes, as listed by the supplier, would be off the shelf. But no, the following day I had a call saying that it was not in stock, and would I like 2×1/2″ instead at the same price?

Drifting off the original question, I know, but I think that the moral is that while having all-metric measuring gear sounds fine, at some point you will need to get out the conversion tables and/or calculator!

[JohnFParticipant @johnf59703]

Frankly it doesn’t matter which system you use,  I’m imperial due to age as you are metric due to age.

Peak4 quoted — Do you already have machine tools such as a lathe or milling machine; absent DROs (which I don’t have) it probably makes sense to have measuring gear in the same units as your machines.

This is really the crux of the matter excepting machines with DRO fitted, if your machines are imperial use imperial measurements and tools and vice versa if your machines are metric.

As I say I work in imperial but also make metric parts — simples !  just convert the required measures to imperial using 0.0397″ = 1mm and machine accordingly then the end result is a metric component.

There are no problems with the imperial system that I have come across in 65 years of machining, fractions or otherwise, fractions just become decimal numbers.

John

[CirclipParticipant @circlip]

After having to go bi-sexual in the DO back in the sixties, I use whichever system is pertinent at the time.

1″ = 25.4mm (NOT two point bl***y five four) and 1mm = 0,03937″ when applied to a number cruncher which doesn’t care what you bash into it.  Me Guzzi is metric and me Venom Clubman is imperial and they lovingly don’t have a problem living together.

Regards  Ian.

[JohnF]

On JohnF Said:

Frankly it doesn’t matter which system you use,  …

….

There are no problems with the imperial system that I have come across in 65 years of machining, fractions or otherwise…

John

John misunderstands the problem I fear, probably because his experience with Imperial is workshop based.   Whilst it’s true that machining is easy enough in either millimetres or thou, the real issue is that Imperial measure complicates the big picture horribly.   Metrication is good for engineering and science in the large, it’s for the thinking end of engineering rather than hands-on.

Machinists are a fine body of men and a boon to society, but they are tiny part of technology as a whole.    Technologists have to worry about much more than length.  Concepts like force, work, power, and energy are all essential for design, and designing anything complicated makes it bleeding obvious that Imperial is badly flawed.

The reason is historic.   Before the Industrial Revolution, units of measure were local.  Trades differed, as did regions, and  everything was arbitrary.  There was no logical connection between measures, making the system internally incoherent.  Despite huge efforts in the 19th and early 20th centuries to tidy up Imperial considered as a whole is a mess.

Imperial being internally incoherent doesn’t matter if the job only involves linear measure or only involves weight, but Imperial is an A1 problem for wider technology.  Imperial calculations generate multiple unnecessary conversions that befog thinking and cause silly arithmetical errors – it matters!

Metric eliminates most unnecessary conversions, making the maths that underpins engineering considerably clearer.  Metric advantages may not be obvious when driving manual machine tools, but metric simplifies design considerably.   Any engineering needing maths is fuddled by Imperial measure.

The UK, I think, made a bad mistake by metricating piecemeal.  Allowing metric and imperial to exist in parallel added another layer of unnecessary confusion that persists to this day.  Unfortunately hard to explain to folk who only use a tiny part why Imperial is a b*gg*rs muddle, but it is!   With hindsight, I think it would have been better to force metrication through quickly.   Sacking and demoting a few diehards would have provided a clear practical reason for going metric to a workforce who didn’t care about theoretical benefits   When the carrot fails, apply the whip!  As is, bodging metrication badly damaged British industry.

Metrication matters now more to Model Engineers than it did.  Anything involving CAD, CNC, electronics, and current stock sizes are all smoother in metric.   But my main message is that encouraging newcomers in 2025 to adopt Imperial is unwise.  Earlier I listed several good reasons for having an Imperial workshop but I hope it’s clear that the list doesn’t include retired gentlemen preferring Imperial for historic reasons, or just because they make LBSC engines!  As Metric increasingly dominates the modern world, I submit youngsters shouldn’t go Imperial unless they have a good reason to do so.

Attitudes to metrication have changed since I first joined the forum about 10 years ago.   Back then any suggestion Metric was better than Imperial caused conniptions!   Now, I think the majority are in favour…

Dave

 

 

[Graham MeekParticipant @grahammeek88282]

As someone who started out in Feet and Inches and then had to change mid-course at ONC level to Metric. I must say I much prefer the metric system. During my career it became necessary to work to both Imperial and Metric drawings using what ever Metrology was available.

It baffles me why there is so much emphasis on being Imperial, because the item was made in Imperial times. They are both after all just a system of measurement.

My Grandson hates it when he hears someone state on a documentary a measurement in Imperial units. He will very often ask me what is that in Metric.

This country so say went Metric, but we still buy things in Pounds, and we drive on roads with speed limits in MPH. Tyres for our cars are in Inches, mainly and most of the timber is listed in metric equivalents to the old feet dimensions they used to be. I still buy 1″ diameter EN1A.

I too remember the “Wars of the Systems” that used to occur on here, if one should blaspheme and even mention the word Metric, or Millimetre. It is nice to see we have moved on a bit.

Regards

Gray,

 

 

 

 

[John HaineParticipant @johnhaine32865]

Just to add to the pedantry, maybe we could stop using the term “metric” and start using “SI”?  When I was at school we did woodwork in feet and inches but science in “metric” which at that time meant cgs – centimetre-gram-second.  Though there were fewer odd conversion constants it was still iffy.  Finally at university I was introduced to SI which is coherent.  It isn’t quite the same as “MKS” because it embraces all measurement including electricity and magnetism.

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