Metrication of models

Re JA's comments under his small screws thread.

I think that as older model engineers give up the hobby and younger ones come along, they will bring their knowledge with them. They will only have been taught metric everything at school so old imperial designs will rapidly decline in demand as the youngsters will not understand them. Too much of a learning curve.

I envisage that many castings in the comprehensive sets will become unavailable due to the total cost. Main demand will be for loco wheels and flywheels since they are a pattern making nightmare and a huge amount of work to hack out of the solid.

On the other hand, a relatively cheap block of cast iron can easily be butchered in the mill to create inside cylinders. Maybe chimney and dome cover will still be wanted to cut the amount of machining but horns and axle boxes, even frame stretchers and motion plates can easily be fabricated. As another example, the bracket supporting Sweet Pea reverser stand can be quickly knocked up from offcuts/scraps with a welder. Point is, only items involving huge amounts of machining will be in demand for a casting.

Younger modellers will naturally go for metric threads. So easy, 6mm threaded hole? easy! use 5mm tapdrill. Think of all the complication of a say, BA thread and a number size tapdrill. Then there are all the other threads and sizes, all with their special series of tapdrills. If expensive sets of everything are not bought, you need to look at the drawings and use the American approach, Bill of Materials, but applied to specified threads and their tapdrills then go and source only those needed. What a performance!

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

Only three countries now use the imperial system, Liberia, Myanmar and of course the USA. The rest of the world uses the metric or SI system. You could of course declare independence and use the FFF (furlong/firkin/fortnight) system!

John

I'm with Peter.

Brian

I am currently going though this exercise with Elmers Mine Engine, no issues so far
2-56 > M2
3-48 > M2.5
5-40 > M3 etc.

Mind you I am still working in imperial for the main dimensions ....

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

By coincidence I'm currently exploring conversion of an Imperial Plan into metric equivalents. I think the method I'm testing is likely to be how youngsters will approach the problem in future. So far it's proving easier than I expected.

In the past I would have sat down with pad and paper or perhaps a spreadsheet and laboriously converted all the Imperial dimensions into metric before sitting down and redrawing everything with 2D CAD. I might have adjusted all the odd metric equivalents into standard values as I went, or I might have tackled that as a second stage/ Lots of sketches, head scratching and mistakes.

Actually, I fired up Fusion 360 and used the original 2D imperial dimensions to capture a 3D model. Fusion 360 (which I believe is relatively weak at handling Imperial and Metric in the same drawing compared with its competitors) allows dimensions to be entered in both inches and millimeters. So, set up to model in Metric mode, typing 1" will automatically convert to 25.4mm. You end up with a model in millimetres that's exactly the same size as the Imperial prototype, that could be CNC'd off-the-shelf.

CNC as a way of producing imperial clones isn't my goal. From the 3D model of an Imperial object I've generated a set of 2D drawings dimensioned in mm. The conversion produces lots of odd looking values such as 14.25" becoming 361.2mm. Now I could work to the odd dimensions or I could round them to suitably comfy metric whole numbers. Doing this manually witha 2D drawing package would be hard work because parts would no longer fit together unless all the dimensions effected by a tweak where also changed. One change is likely to trigger showers of consequences, hard to keep track of and easy to get wrong. But, I'm not doing the job manually, I'm working with a parametric model where the effect of changes are much more obvious, automatic and instant. It's also possible to fix certain coordinates and dimensions within the model so that whatever else happens, key area remain sacrosanct while non-critical dimensions are free to dance.

All this makes me optimistic about the ability of youngsters to cope with Imperial measure. Being computer literate and having access to powerful tools means converting Imperial to Metric won't be as painful as might be feared. The youth don't have to understand imperial or do the calculations themselves.

Yes my summary is simplistic, but so far my exploration of 3D CAD as a way of tackling an actual conversion job has been surprisingly straightforward, requiring much less thought and care than I feared.

No doubt the gods will punish this post by dropping a showstopper on me during my next CAD session. Serves me right!

Dave

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.

I think the word "Use" is interesting John.

I go to Canada quite regularly and often take the opportunity to pop into Canadian Tyre and pick up any small US threaded fixings needed for some of my machines. They (CT) certainly have metric fixings in stock but so much stuff comes across the US/Canadian border that I don't see any evidence of US threads going away there any time soon. So whilst there might only be three countries officially still Imperial - I think there are probably quite a few more still using it...

I certainly have large stocks of BA fixings for my modelling and will continue to use BA to both maintain & repair my existing models but also any new ones. Most of my machinery was also built 'pre-metric', so they need imperial fittings too. However, when I'm making (new) larger stuff I obviously do use metric fittings simply on cost and availability grounds. Fortunately I can live quite happily with both systems...

Regards,

IanT

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

We were going metric before we joined the Common Market. I remember the hassle at tech, which I left in 1969, with the change to Newtons from the sensible lbf.

Just to keep us oldies happy the metric system does have a M6.35 x 1.27 x 55degrees thread.

JA

Edited By JA on 04/10/2019 17:41:06

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

For me the biggest issue with the US and older UK plans is not threads, but the use of fractional dimensions. They are OK for woodworkers but don't sit well with the lathe or DRO. A recent rediscovery of my 1980 Zeus book really helps here.

... 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.

That would be "Canadian Tire" ?

Canada is nominally metric as a country but mostly imperial in engineering because of the US. Engineering involving scientific apparatus and similar tends to be in metric.

It's still much easier to get imperial sized tooling, hardware etc than metric, although a (somewhat limited) range of metric gear is available if you dig for it.

Edited By Bandersnatch on 04/10/2019 18:29:10

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

Tim,

When you have removed your tongue from your cheek, please tell me what is the metric equivalent of a number to the base 10?

Wots a slide rule? A longitudinal log table? I only calculate as a rule.

Noah told the animals "Go forth and multiply"

"We can't said the Adders"

Later Noah found lots of little Adders.

"How come?"

"We found some log tables"

Howard

how do we switch off the predictive text?

Edited By Howard Lewis on 04/10/2019 18:57:47

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.

Another Canadian here (waving hand furiously) and, I'm now retirement age, and ALL of my schooling was in metric. My first locomotive (LBSC Tich, followed the words and music) was inch and BA, the second wasn't, as metric is just easier for me.

I do build my models in metric, with metric fasteners (the local REAL tool supply store, not Canadian Tire nor the USA-based Home Depot) stock lots of metric stuff - seems like more and more metric fasteners are on the shelves. Now, ask them for BA and you'll get a blank stare.

Materials, because most of them come in from the USA, are most likely in inch format.

Ask ANY kid here how many inches in a foot, and you'll be lucky to get the correct answer. If you do, ask how many feet in a yard...

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