Engine plans

Hi all, I've just picked up a copy of Ray Hasbrouck's Steam Engines. The dimensions are in that old imperial stuff that us young 50ish ones don't really work with. Is there a set of drawings around for his No 3 engine in metric? If not I'll just have to sit in front of cad for a while and convert them.

Ian

Why not use imperial and learn a new skill, nothing wrong with imperial, beats that nasty french metric hands down. I did this with a project, good imperial tools are very cheap, and dro's can work in both metric and inch.

You may want to take a look back through the "Workshop Progress Thread" as Jim Nick has recently completed the same engine and altered some of it to metric. Finished engine part way down this page some earlier posts show its progress

As it is not a big engine a simple conversion is to allow 1/32" on the drawing to equal 1mm which makes it a bit bigger but you will end up with whole millimeters rather than many decimal places.

This means you don't have the need to decide to increase or decrease a stock size to a nominal metric one. For example if the part is a 3/32" threaded shaft you can simply use 3.0mm dia stock and be able to thread it M3 rather than deciding what to do about threading a 2.381mm diameter.

Hurrah, we're off!

Imperial is fundamentally wrong because it's internally incoherent. On top of that it's stuffed with complicated artificial relationships between units and sub-units, for example, there are:

• 437½ grains in an ounce
• 16 ounces to the pound
• 14 pounds in 1 stone
• 7.142857 stones in 1 hundredweight
• 20 hundredweights in 1 ton

Although individual members are cuddly, the Imperial family is dysfunctional. Taken as a whole, the Imperial system is a mess. When the Imperial system is applied to scientific and engineering calculations, everything still works, but the inconsistencies hurt. Formula are less understandable and using them error prone.

For simple work Imperial is often convenient, like being able to divide 12 by 2, 3, 4 and 6. Unfortunately, that convenience turns into a disability once you get beyond straightforward problems like sharing out cake. When the maths is difficult, the Imperial system has no fans.

Related issue with fractions versus decimals. If you live in a world where most things divide neatly ½, ⅓, ⅛ etc, fractions are a good idea. Calculating Gear ratios is an example. But it's a bad mistake to imagine that fractions extend naturally to other problems, they don't. It doesn't take much complexity in a calculation for the advantages of decimal to assert themselves : as a system, decimal is more general than fractions, which is why fractions rarely appear in the metric system.

The only reason Imperial survives is the number of people steeped in it. Doesn't mean it's a good system. Much dafter ideas than Imperial have lasted centuries because millions haven't had the time, effort or desire to change.

Dave

I did buiild my version of this engine in Jason's link using metric units but while converting I reduced the size because to my eye the engine was a bit long with not a lot of moving bits going on . I used a photocopier, a calculator and some Snopake to arrive at my working drawings, no CAD to share I'm afraid.

Jim

Think you got US contamination there. An Imperial hundredweight is 112 lb, or 8 stone.

Oh, and there's been some study a few years back that showed people adept at Imperial calculation are more flexible at mental arithmetic than those who just shuffle the decimal point back and forth... 

Edited By Mick B1 on 07/08/2018 10:10:45

Having many imperial tools and old but excellent imperial machines I naturally welcome imperial drawing dimensions but I have had to work professionaly with both systems so I really am not bothered by mixing them when making things. A lot of what I do now is restoring parts of vintage motorbikes which are generally measured in inches anyway. I do have a metric micrometer, digital calliper and a DRO so conversion is easy anyway. Incidentally , what's imperial weight got to do with machining things? Colin

Being able to work in metric and Imperial (which normally requires both fractions and decimals) is useful in a hobby where so many designs, as well as the prototypes from which they are derived, were originally in imperial or US customary units. It is also quite a stimulating exercise after a career which has been almost entirely metric, even if it has often involved materials such as extruded angles 25.4 x 12.7 x 1.6mm, or getting very upset at people who put 1/4 Whit nuts into a bin of M6.

In some drawings Imperial or BA threads are used with metric dimensions. This is particularly common in 16mm/ft models, but hard to complain about given the scale ratio and in other cases either metric or imperial materials are hard to find. My mental arithmetic is far too slow for this, so I have made and laminated sheets showing 64ths/thou/mm and refer to them frequently.

Brian

When I was working as a toolmaker fractional dimensions were only used for an unimportant dimension such as the base of a drill jig and had a tolerance of +/- 1/64 th of an inch. Apart from standard threads, everything else was dimensioned decimally anyway, normally in "thous", e.g. 1.002, often in "tenths", e,g, 1.0002, so it was very similar to metric dimensioning apart from the basic unit of one inch as opposed to one millimetre.

Why don't fraction-o-philes have micrometers which read in 1/1024" (the logical progression from 1/2, 1/4 etc)? Simple answer because fractions are extremely unwieldy when you get beyond simple stuff. This from someone who started out bi-lingual in cgs and Imperial, but for the last many years of employment used only SI for calculations because it's less prone to errors introduced by the wierd 32.2, 384, 770, 550 factors which you have to remember. As for someone brought up in metric being encouraged to learn fractions, let's get real. If young people are to take up model engineering they are not going to learn a new illogical language.

I am amazed that people can take up fixed positions on this topic. I am equally at home with Imperial and metric dimensions and sometimes even mix them together on a drawing!

There is nothing difficult in either system. Neither is logical if you delve into them. At this point I will take cover.

Andrew.

No need. I think there are plenty of us to give you covering fire...

Quoting rubbish like;

• 437½ grains in an ounce
• 16 ounces to the pound
• 14 pounds in 1 stone
• 7.142857 stones in 1 hundredweight
• 20 hundredweights in 1 ton

is to use misleading information to try to make a point.

Brian

Hmm.

The advantage of imperial is the 'powers of two' subdivisions make it very easy to design things in good proportion while ensuring small parts can add up to sensible sizes.

In metric you have the choice of powers of ten, which are obviously too big, or using 'preferred sizes' which have the problem of rarely being able to be combined to give convenient larger sizes.

So while metric is much more logical, imperial lends itself to design of mechanisms where you need lots of bits to 'add up'.

Neil

I do work in imperial when required but to me its not a "natural" thing to do. I prefer metric and find it much easier but I suppose its what I'm used to. Most of the machines I work on have various imperial fittings for gas supplies and coolant so that's where I use imperial mostly these days. The exception being one machine where the gas fittings were also metric. That confused the hell out of me for a bit.

The bane of an editor's life... obviously unavoidable when using certain stock parts, but otherwise...

Trying to change someone's drawing is out, it's too easy to introduce errors that way.

Neil

No Brian, not misleading at all. You're thinking of the hundredweight of 112lbs that was discontinued as a formal unit 33 years ago. In the US they still have a formal hundredweight but it's 100lbs, not 112. The US hundredweight still has legal currency as a working unit, while the UK hundredweight has joined the farthing as a bygone. Some people know what it was but beyond that it's rarely used in the UK except as a source of confusion.

Interworking with the US, there are 20 US hundredweights in a ton (2000lbs), and there were 20 UK hundredweights in a ton (2240lbs). That's quite a difference, so to avoid confusion the Imperial system still has short and long tons. You have to be careful when doing sums.

I'm afraid the Imperial system isn't just a muddle, it's an international muddle. The case for the prosecution is that Imperial presents like a cuddly uncle, when actually the chap is a liability. Imperial measure is the Harry Worth of metrology.

Dave

Edited By SillyOldDuffer on 07/08/2018 18:48:35

I have a metric lathe and mill.At present I am building an American design Ic engine in imperial.It is no obstacle to use the caliper in imperial to the drawing dimensions and then press the button to metric,I can't see any problem.

Frank

I have known very skilled people, Toolmakers, Fitters, Machinists, Cabinet makers, Carpenters, probably more skilled than most around now, who for nearly all of their working life used imperial. They seemed to cope alright. Also you speak as though imperial is dead and buried, its still used in America, and then by people here who work on American products, such as train locomotives, and aircraft.

I worked for years in a hose company, machining threads on fittings, making up hose assemblies etc, all in imperial, usually BSP, British standard pipe.

Today the only sensible thing to do is to work with metric dimensions because that is what tools and materials are generally available in.

However to talk about a single imperial system is a little misleading as there were many many different sets of units used in different situations - those suitable for a pharmacist making up a medicine were ideal for that but not suited for bags of coal. Similarly the units used by a jewellery maker were not suitable for a manufacturer of steam locos. Despite all of these different sets of units (and more) there was rarely any need to convert between them. Horses for courses.

Along comes the metric system and all of a sudden it is time to try to use a single set of units to cover all of these situations - I say a single set but during my lifetime (and I am not yet retired) I have used imperial units, cgs, mks and SI units in science and engineering. Things are still changing - the most recent I am aware of is the change from 1 kilobyte = 1024 bytes to now referring to 1000 bytes.

Unfortunately the system of units used for most of the history of model engineering was fractions of inches, number and letter drills and gauges for tube, sheet and wire thickness, If these tools and materials are no longer available then yes, you do need to convert - but this trivial using a calculator, provided that clearances and strength of components are not compromised. the original designer might have erred on the tight side for example, and using a standard conversion might be just too much - common sense has its place here.

I have in front of me a drawing by Martin Evans that includes number drill sizes, fractions and decimal inches and it is not the easiest to follow to say the least!

Nick.

PS Recently I tried to show how easy it was in the 1970s when I had to do 12.5% VAT in my head. This was done by working out how many half crowns were in the total sum - it degenerated into confusion when I realised the person I was talking to had no idea what a half crown was. I must be getting old!