Metrication of models

.

A reasonably serious question, if I may ...

If you are doing such a conversion ‘thoroughly’ as proposed : At what point does it cease to be a scale model, and become a new design ?

I don’t expect a definitive answer ... just want people to think about it

MichaelG.

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

If you are modelling a prototype that was built in metric then use metric and if (like me) you are modelling a prototype that was made in Imperial then use Imperial.

I was fortunate in serving an apprenticeship in a company that used both but did no converting, we were expected to use the appropriate system.

Brian

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

Not sure that one holds water because most imperial machines and their owners work in thou, not fractions. 1 3/8" is OK because it happens to work out neatly to 1.125". Plenty of other common inch fractions are less cooperative, for example: 1/3" is 0.333333 recurring, 3/16 is 0.1875", and 7/64 ie 0.109375". That inch fractions don't always translate neatly to thou doesn't bring Imperial workshops to a shuddering halt, and neither should 34.925mm.

Personally I find it best to avoid fractions in both Imperial and Metric. I wonder when the last professional mechanical engineering drawing used fractions? 90 years ago perhaps. My 1907 ICS Book insists measured or gauged dimensions be expressed to 3 places of decimals, fractions forbidden. It also explains how to design to the nearest 1/64th of an inch, this being the accuracy expected of most metalwork before thou accuracy and tolerances became the norm. 1/64" is an eyesight limit and no-one uses the method now because we all have calipers, micrometers and DROs. Time marches on.

Dave

I can see why

And I used a calculator!!!

ARGHH....

Oh my word; eighths and sixteenths in decimal should be instant recall!

I still use 64ths, albeit not explicitly. If I'm machining a spigot that is, say, 3/8th long I'll hold a rule on the toolpost on the first pass and knock off the feed just before 3/8". The I'll turn the spigot to the correct diameter and finally take thin cuts off the shoulder. After each thin cut I put the rule on the work, resting against the shoulder, and if the end of the spigot is within a lines width of 3/8" on the rule that's good enough. If better accuracy is needed I'll dig out the depth micrometer.

Andrew

Dave, a lot later than you think. I volunteer on the Mid Hants at Ropley. The 'BR' not Southern drawings done at Ashford in the 50's for Spam Can tenders are all in fractional inches, with a few odd dimensions mainly diameters in decimal. As an aside in 40 years of professional engineering, these drawings are some of the worst I have ever come across.

Dave

I was a contract drafty at a machinery company in the early 70s. They used fractional dimensions on casting drawings, decimal dimensions on fabricated and machining drawings. It made some sort of sense at the time!!

I started work for the MoD (N) in the mid 70s and had the privilege of working on what I was told was the first "metric" ship built for the Real Navy, (the Type 22 class of frigates).

cheers

Bill

Imperial may be dead in manufacturing drawings, but ten years ago I was still drawing components with 7.2mm holes in 1.6 x 1.6 x 19mm angle.  Good practice for 16mm/ft scale models where a component 1/8" Dia x 64mm can turn up on a drawing.

To be fair, the metric system has only been fully legal in the UK since the 1880s, and we don't like to rush into these things.

Brian

Edited By Brian G on 05/10/2019 08:51:35

Those with no background in imperial will also find it hard to understand scales like 3" and 6" but may grasp the idea of 1/4 or 1/2 scale.

They are more likely to be used to the preferred metric scale of 1:2, 1:5, 1:10, etc so may choose to make a traction engine at say 1:5 which in all probability would like imperial loco builder do be done at 5mm to the inch or 1:5.08.

Or they may go the way of figure and railway modellers as mentioned above and use a mm/ft or inch ratio. so that old imperial 3" traction engine would not be too difficult to build using 8mm/1"

The comment that it is hard to find metric stock really only applies to small lengths bought through UK ME suppliers. Trade suppliers will carry more metric than imperial and you would have a job to get imperial materials in mainland Europe or many other countries that have grasped the metric system.

In your dreams, like we'll be reverting to pounds shillings and pence as well. Only old f*rts like us understand imperial, and I for one much prefer metric, just give it a go, it's easy

Like many on this forum, I was educated in the feet and inches era, when "times tables" were learnt by rote and were handily available on the back cover of our exercise books, along with conversions of rods, poles and perches. When we moved to France, I had to decide whether to make my workshop metric or stay Imperial. I chose metric. A couple of year ago, and now back in the UK, I purchased a Worden T & C grinder kit from Hemingway and was surprised to see that the drawings contained a mix of Imperial and metric, fractions and decimal. I decided to convert it all to metric and redrew all the drawings. It took a long, long, time. I offered them to Hemingway, but they declined the offer. Sadly, I lost the lot in "the big hard drive crash of 2018". I haven't had the urge to do them again.

John

I'm currently metricfying (is that a word and have I spelt it right?) the Farmboy Hit & Miss engine drawings. I started off just doing a 1" = 25.4mm conversion but ended up with some odd metric sizing and I still had to deal with standard stock sizes. Lots of dimensions can and have changed and it is a lot of work to ensure parts still work together.

Here's a question though: Once I am finished and built it are the metric drawings I have created now mine to sell or are they still subject to the original copyright?

With regards to Metric fasteners. If you can't source them from your own country then you can certaining get them from Aliexpress easily enough.

Cheers

Bruce

Bruce. Metricating does not change copyright. I believe a design has to be substantially changed to create a new copyright. Consider people like Dyson etc and their copyright infringement cases.

Hi All,

I sit here after a hard day at the track, chuckling at the fresh can of worms I've opened, to fit alongside JA's!

I am the " wrong" side of 70 but feel comfortable with Imp. or metric, since I had both to contend with at school. At the time, couldn't see the point of this new - fangled decimal system except in Science lessons where it proved to be SOOOO much easier to use.

Duo-decimal currency, "2 farthings = a ha'penny, 2 ha'pennies = a Bob, sorry 1 shilling" and so on.

As mentioned above, rods, poles, perches, chains, quarts, 8 pints = 1 gallon, 112 lbs = 1 cwt. What a load of old medieval crap that belongs in some countryside museum. Thank goodness it's all going. I am now however, very grateful to my school for teaching me both systems so I can easily use which I choose. It's simply so lovely to just shift a decimal point when doing mental arithmetic. Still difficult to visualise some things, e.g., I have seen pictures of new cars dimensioned in thousands of mm! What you absolutely must not do is try to convert due to the extremely awkward equivalents. Must choose and stick to the one system throughout a whole build project. Enough drawing errors without an exponential increase caused by conversions followed by rounding off dimensions.

Edited By DMB on 05/10/2019 22:47:56

The world moves on at what seems like an exhaustingly quicker pace. Or am I really slowing up at an alarming rate? Ha, ha!

All of you older forumites have experienced the tsunami of modern technology, same as me and some have picked up the baton and run with it faster than others. I look at things and think, can I make good use of this or that, or not? E.g., much better to have mobile in pocket than have to walk 1/2 mile to BT phone box and then find it smashed up and out of order. I have taken on board small things like led ring light for vert. mill, electronic rev counter for mill, lathe, bench drill. Dro s for mill. VFD on lathe. Mitutoyo elec. calipers. I just about cope with 'puters sometimes with a little help from my professional programmer nephew but to try to use it for 3D modelling is a step too far. While I would be struggling to master that, I would be losing a lot of time to do other things and life is rapidly getting shorter! Don't tell me that it would eventually save me a lot of time. I cannot see any great use for it for me. Mechanical stops and Dro s are perhaps a sort of halfway house but which I can make immediate good use of.

It all depends upon what you want to do.

Lease EU and revert back to Imperial? I hope not. We will probably become more aligned with USA for trade, using Imp for some types of business and metric to trade with the rest of the world. Just wish Parliament would obey a referendum result instead of keep trying to kick it around til they lose it. What's the point of having one if MPs want to ignore it? Get it sorted, move on and complete the metrication process which has also gone off at half- cock. Let's have some real progress and leave us old codgers to continue playing about with BA and BSF! Sod it, I'm  tired, it's late, cat out on nightly prowl and I'm off to bed.

Edited By DMB on 05/10/2019 23:28:34

Huh?