I thought that when we left the E.U. we were going to revert back to imperial measurements in line with

the US of A and the rest of the world

I'm with Peter.

Brian

The US don't use the Imperial system, they use "customary units". Some are the same as the UK, others, such as gallons and US Survey Feet aren't. Threads are even worse as they don't use Whitworth, BA (apart from darts), BSF, BSB or ME.

Fortunately my 24 year old son (and his DRO) switches quickly between measurement systems as required.

Brian

Edit: At least on the mainland they use BSP

Edited By Brian G on 04/10/2019 17:08:43

It's predominantly a case of substituting alternate threads which will work (i.e. not having an over-size major OD which interferes with another aspect of the part) and using a calculator.
Anyone working in metric and unable to machine from an imperial print should find themselves a new gaming machine to play with as that's all they're good for.

Simply converting imperial dimensions to metric isn't really going metric. To do so properly one needs to convert part sizes to use readily available metric sections. Are you really going to machine an axle to 9.525mm over its length rather than use 10mm stock?

Andrew

There is a lot of tosh written about the 'benefits' of the pre-metric measurement systems. Most of them seem to forget that the metric system grew rapidly in popularity around the world of commerce because it enabled everyone to overcome most of the objections to the older systems. Not only the confusion of how may whats make a wossname, and a different number each time – think ounces, inches, stones, shillings, barleycorns, pennyweight, drams (apothecary, avoirdupois, troy), grains (ditto), scruples, bolts, cables, chains (4 sorts) fathoms, furlongs, hands, miles (5 sorts), nails, points (3 sorts), rods poles and perches which were the same or not, depending, and townships. A further difference for us was being able to order material from anywhere (except the USA, where the postage rules it out anyway) and know what you were going to get.

I suppose the next solution to the problems of metrication is going to include logarithm tables, slide rules, and quite likely, the casting of lots – good luck.

Cheers, Tim

… not to mention using metric standard tool radii …. not to mention re-doing your fatigue testing if the change in tool radius might affect it …..

Been there.

I'm with Andrew on this one that designing or updating a model to metric is more involved than just doing a mathmatical conversion or clicking an option in your CAD. As well as the obvious point he made about using stock sizes other dimensions are better adjusted to whole units, who wants to try and machine a part that may have been 1 3/8" to 34.925 long when 35mm is a much simpler figure and makes mental calculations easier if you want to place a hole in the middle or work out a tool offset.

There will come a time when getting the old imperial sizes will becomeeven harder, you already pay a premium for imperial as a length of 10mm 230M07 is generally cheaper than 3/8" EN1A. As for those BA fasteners several now come with the nearest metric hex as BA A/F is becoming harder to find particularly in the non preferred size such as 5 & 7BA which the ME user likes.

As Bandersnatch says tool size also comes into it, far more choice across the price range in metric cutters than imperial and make the slot or groove to match the cutter not an odd decimal size When drawing up an engine I'll now think about the common size cutters and make parts to suit and now I'm even thinking how the part may be CNC machined and what best suits that method

I agree with DMB that the number of castings available for a given model will start to reduce as the simpler parts will be cut from solid or fabricated so the supplier won't recast slow selling items and tie up capital that will just sit on the shelf. It is already getting harder for them to find small batch foundrys and to get quality castings.

As for the future of plans, when was the last one added to the old Myhobbystore (now Sarik) range? I think it was the Nemett Lynx which must be at least 10yrs ago so the new designs being published will only be available from back issues or digital archives. We have yet to see commercial plans being sold in digital format but several of the guys on other forums who design their own engines are selling digital sets of plans. Will there come a time where the plan package will also include STL files or whatever the current file type may be as part of the package so that builders can then put the part through their CAM package and produce parts by CNC or printing. Certainly something I would be happy to add to any of my designs that may be published in the future

I am three years into making a 3 1/2 “ Evening Star, slowly. While following the book and plans with regard most dimensions, drills are metric as are reamers, taps and some material thicknesses. When I started I was going to create metric drawings and model in Fusion360 but quickly decided to mark up copies of the drawings as I went along. I’ve only bought the expansion link brackets and cross heads as gunmetal castings but needn’t have bothered as the castings are more trouble than making from scratch due to material thicknesses and out of position elements make machine to drawing near impossible. So far the rolling chassis is nearing completion.

Fortunately I feel at home and competent with both systems. The thing that fouls things up is the availability of of stock material and fasteners. As a price premium is beginning to develop for non metric tools and materials and in the case of models many people make fastners to suit with non standard heads then I am beginning to think that why not use the most convenient threads and stock. Many things can be changed to the nearest metric size without making a problem. If you do build a published design and deviate then anyone who may inherit the item may curse a hybrid but I think I would just please myself. I have amassed a significant collection of all flavours of taps and dies including a rather nice set of LH BSF taps and dies, it was a rather comedy moment when I realised it was LH when I got it home, I still can’t decide whether I would have bought it had I realised. I wonder if I will ever use it?

Mike

I re-opened the very old Small Metric Screws because I am about to design and hopefully make a metric model steam engine. My definition of a metric model is that, in addition to metric screws and nuts etc, all the dimensions would be based on millimetres, not inches either decimal or fractions. In other words the bore of the cylinder would 25,00mm not 25,40mm and so on.

Tooling for such a model is very easy. You can buy any cutter, drill, tap or die in metric sizes. I am told you can even buy metric lathes (a Myford owner here). However it soon became obvious to me that small un-plated mild steel screws and nuts were not readily available. Hence I re-open the old thread.

Happy with the replies I was not going to go any further with the thread however DBM decided to run with the subject.

I now realise there is at least one further hindrance to the concept of a metric model – An awful lot of material is still only sold in imperial sizes.

I had not intended for this to become a rant for S.I. units or inches (fractions or decimal). They all have their good and bad points and I am happy using any of them. All I want to do is to try a build a metric engine of my own design.

JA

Michael, I would say that many "scale models" are not made to exact scale. Take Loco's for example if they were built to a ratio of model gauge divided by full size track gauge you would have very few parts that equated to stock sizes, available threads etc. Same for all those 2" scale traction engines as the inch is not easily divisible by 6. Then there are the other factors such as being able to cast in scale thicknesses or leaving out detail to keep cost of commercial castings realistic.

I am sure there are those that will make totally true to scale models but their numbers are limited and if the model is to run then ones that are totally scale will be almost non existant.

Edited By JasonB on 04/10/2019 20:24:59