Why is the world of model engineering still imperial?

Not trying to be antagonistic, honestly, just asking really, why is the world of model engineering still in imperial? we have been designing buildings in mm for over 40 years.

I remember from my teens using BA threads and imperial threaded fittings from Stuart Turner but I wonder why we still seem to be working in this world?

Says the bloke who has just had to buy a set of BA taps and dies! :0)

It's a good question.

Off the top of my head I get think of 3 reasons:

Most of the published designs are old or from the US

The old machines that we repurpose for ME are imperial

Most of us are old gits

Rod

Apart from 5BA and 7BA hex-head bolts in exposed areas for cosmetic reasons, and 10BA round-head screws in some areas to replicate rivet heads, all other threads on my non-steam loco are metric.

Steam loco currently under construction has 6BA for all cosmetic bolts, metric elsewhere. Have not progressed to boiler and cab yet so may need to revise this later.

If only someone had the necessary financial resources to produce a range of metric hex-head steel bolts in the smaller sizes matching BA up to say 10BA. Smallest I have found locally (Australia) is M3 and only in Stainless Steel.

There's nothing wrong with imperial.

Another old git

Roy

Depends what you call the model engineering world, I've done several models form designs that originate in mainland Europe and they are metric and my map has europe as part of the world.

More likely most commonly built designs are 40+ years old and have not been updated but there are a good few metric ones about now all my published ones are and a lot more that have not been published. All those Elmers kits that your supplier sells are based on designs from the US that are Donkeys years old so that is why your engine is in imperial but as the parts don't include fixings you could easily have substituted metric rather than blindly follow the drawings.

Perko you can get small hex metric fixings, I use them all the time brass, steel and stainless M1.2 to M4

Edited By JasonB on 03/03/2023 12:21:09

I'm not sure it is still Imperial Paul - most new machine tools (here in UK) are metric, as are much of the tooling used with them. I work in both metric and imperial in ways that make sense to me but maybe not to others.

All my machines are imperial. My CAD designs are in metric and I (mostly) use metric drawings. I have a mix of metric and imperial tooling. For my 'model' engineering, I mainly use BA screws and threading/tapping tools because I have models that were built with them and I still have ample stocks of both. For my 'engineering' work (jigs,tooling,accessories) I generally use metric fixings (M2 up) because they are inexpensive compared to imperial these days. When I'm working/repairing my machines, I use imperial/US screws because that's how they were made.

So it's complicated but mostly down to personal preference and habit. I generally think in feet, yards and miles for larger distances, millimetres for most things between 1000 and about 4mm - and 'thous' when I'm machining. A friend of mine uses imperial measures exclusively but 'decimal' imperial (not fractional) - which works very well for him. I do this myself sometimes - it's often easier to 'think' of 1/8" as 0.125" (or 125 thou) as a simple example.

I should add that BA is based on a metric system and still works extremely well (as do the ME 32/40 threads) for the kind of work that many do. Once you've got used to remembering that 1mm is (about) 40 thou - then things become much easier too.

Regards,

IanT

Edited By IanT on 03/03/2023 12:21:47

And most things were easily scaled down from feet and inches drawings to feet and inches models? Fairly obvious when most model engineers were still only using imperial machines?

If a workshop was set up with Imperial machines and measuring equipment, having to calculate evry dimension from metric into Imperial is a PITA.

Many of the models that are still being made are to drawings that were produced way before 1971 and UK deciding to go metric.

Anyone restoring old machines (Unless continental ; machine tools, tractors, cars, motor cycles, locomotives, agriculktural equipment is likely to find that many, if not all the dimensions are Imperial d r

And they are only dimensions.

As long as there is enough material to fulfill the purpose, does it REALLY matter?

A 12 mm shaft and bearing will perform as well as a 1/2 " unless pushed to the absolute limit..

BUT, a model of a machine originall made and built with Imperial fasteners might look a bit strange with Metric fasteners. Especially to the fastidious.

And working on a machine with a mixture of threads / dimensions can be frustrating, to sayb the least. (The Bristol RE used a Gardner engine using Whitworth thread forms. But the bell housing was fixed to the engine using nine 3/8 BSF bolts and three 3/8 UNF nuts. And the rest of the chassi fixings were Unified.

The Leyland Leopard chassis was to Unified standards, but was powered by the 0600 or 0680 engines to Whitwirth standards.

Both were sources of frustration to fitters!

And for some purposes, Imperial may be better, such as 40 tpi Model Engineer threads.

And the Continent still uses Imperial threads . We call them BSP, they call them "gas" or "gaz"

Howard

Because fractions like 27/64ths are so much easier to use than big long numbers like 17.05mm.

As said, almost all designs and available castings are old. Fixings are dominated by BA (OK, they are Metric but that is not relevant) because they are readily available.

If you want to spend some time take an old design (of anything) and try to convert it completely to Metric as a paper exercise. In theory good looking small metric nuts and screws are available in the UK. I have found two suppliers: One has a lead time of over a month and their nuts and screws look OK although they are stainless steel, the other imports from Germany and I have waited about a year for my small order which is yet to arrive (just to take a look ay their quality). Ordering from Germany was far quicker. As for Metric rivets, make your own, I have only found one supplier and the rivets are stainless steel.

This will change very slowly. It costs money to change and the market is declining (for fixings, castings, designs and major hardware).

There is nothing wrong with either Imperial or Metric. It is far better to be in the workshop than having a fake arguement.

JA

Dividing by 11 1/16 for 5" g locos is really easy. Using metric might encourage younger people, who simply don't understand imperial, and we wouldn't want that would we

Who cares!

I use metric and imperial, both for hobby and commercial machining as appropriate. But then again I'm making parts, not sitting in my armchair.

Andrew

I use any standards that are called for, be they metric, imperial or even older standards. It causes me no problem. The only downside is that you need extra kit. But again that isn't a problem for me as I repair old stuff that calls for just about any of the thread standards you could think of. So having lots of different tooling is a benefit.

Andrew.

JA I also get my metric fixings direct from Germany, the same company GHW has a bit more in their range of metric rivits in several materials, usually 3-4 days DHL delivery

Converting old designs to metric need not just be a paper exercise. I've done it many times right through to the metal bit and I don't just mean using 25.4 conversion and kidding yourself that a 6.35mm shaft is metric when we all know it's a 1/4" shaft expressed in metric. I change all stock to nominal sizes, ditto fixings including fine pitch metric in place of 32 and 40TPI and may well alter the physical shape of the "castings" to whole digit metric which just makes it so much easier when machining if you want to allow for a tool offset or work from a ctr line datum. There are also a couple of simple conversion ratios that can be used particularly if you want a larger or smaller version such as 1/16" = 1mm or 1/32" =1mm

As to sticking with old imperial castings, I think my views on that have been covered well here in the past.

Edited By JasonB on 03/03/2023 13:27:53

I've had modern stuff via Lidl that's still got Imperial fixings

The Chinese make stuff for the USA market and send rebadged ones to the EU

If the USA switched then Imperial would go

LOL, thank you for all of your replies, as an old git my self I am quite at home with either system and yes I had heard the BA threads were based on the metric system, i just wasn't sure that I should believe them or not!

I often have to correct my self when i use expressions like , "oh you know about 2" quickly followed by "50mm"

Old habits die hard and being able to half and half again etc is a nice feature of the imperial system.

When measuring up for furniture etc I use which ever system gives the result closest to a whole number or easiest to remember!

BTW I will try to remember that "1mm is (about) 40 thou". Thank you for that one.

Edited By Paul McDonough on 03/03/2023 13:47:53

Edited By Paul McDonough on 03/03/2023 13:48:26

Thank you for the suggestion JasonB, "<>Paul, if you want to try a metric wobbler after that imperial one have a look at this" that looks nice but i have a H10 lined up for my next project,

I just hope i haven't bitten off more than I can chew.

Metric is great when dealing with whole numbers, but imperial is inherently geared up to provide fractional measures to get you in the ball park and dial in a dimension. It's 6 and half a dozen when using a DRO, but for anything that wants measuring to the mic gauge, I'll take imperial every time given the option. Additionally, and this could be an autistic brain thing rather than a rule, but I find there's patterns to imperial measurements that I just don't feel in metric...

J

I agree

I suspect that the preference for Metric or Imperial might depend on what machinery you have. My outside workshop has an Imperial ML10 bought new in the early 1970s and an Imperial Centec 2A Mill which is probably twenty years older than the lathe. Everything in the workshop is Imperial and the only conversion I make in there is fractional to decimal to use the lathe or mill handwheel readings.

My inside workshop is Metric with a relatively new Cowells and a Sieg KX1, so everything done in this workshop is metric with metric measuring tools. So I have to switch from Imperial thinking to Metric thinking and vice versa when I move between the workshops.

I have no real problem with switching between the two. At my school in the 1950s Physics was taught using the cm/gm system and Applied Mechanics using ft/lb.

Jim.

Edited By Jim Guthrie on 03/03/2023 14:40:38

Edited By Jim Guthrie on 03/03/2023 14:41:25