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

There's nothing wrong with imperial.

Another old git

Roy

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

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

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

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

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.

<>Paul, if you want to try a metric wobbler after that imperial one have a look at this

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

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 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

Just to keep the fractions brigade happy I'm thinking of making a range of micrometers which read out in 1024 ths. This is 2 raised to power 10. You can't have it both ways, if you want fractions, you're cheating if you suddenly go to decimal inches when you need some precision. This argument is futile anyway, no young person understands Imperial, even in the USA science is conducted in SI, and I believe the space programme is in SI after an unfortunate mis understanding.

I'm old, I have an imperial milling machine with DRO, I habitually use it in metric, it's easier