Stuart D10 Metric Plans

[Neil WyattModerator @neilwyatt]

Hi Stephen

You didn't explain it was tedium rather than knowing the methods that was your problem! There are plenty of younger people who have no experience of using fractions, so hopefully these posts will be of value to them.

As for Stuarts, they will change if they get customer demand, but I know there's a cost to having the drawings redone and proven in metric as this means converting to use sensible units (e.g. 6mm for 1/4&quot rather than just converting each dimension. Presumably they just don't get enough requests for metric drawings for it to be worth the investment?

Neil

[John OlsenParticipant @johnolsen79199]

About thirty years ago there was a metric version of the Stuart 10V published. The Unimat lathe people at the time were providing a set of castings with a booklet, all in metric. I would still have my copy somewhere, but please don't ask me to find it at the moment. As already mentioned a D10 is just a doubled up 10V.

But anyway, my experience of Stuart castings over the years has been that quite often there is not enough metal to clean up to the nominal size, so you end up making changes to get the fits anyway. For instance a valve chest which the drawing says should be machined to half an inch thick will already be a hair under half an inch in the rough cast state. So you have to have a think about the effect that will have on other dimensions anyway. Not so bad with valve chest thickness, but with some items the effects can be far reaching.

John

[Stephen BensonParticipant @stephenbenson75261]

I worked in Drawing Office for a time and was tasked with getting the Draftsmen off their boards and on to computers it turned out to be much easier than you would think as they could see the advantages, production trebled in a matter of weeks. One of the thing we were very keen on was that they should make it easy for the machinists to read and use no calculations should be done on the shop floor everything from a common datum making use of the digital readouts all the machines had so I guess I am a bit more sensitive to bad drawings than most especially as I know how quickly they could be redrawn.

Edited By Stephen Benson on 31/07/2014 10:14:24

[Ian S CParticipant @iansc]

To no one in particular, to be a model engineer it is some times an advantage not to be a professional engineer, it's a branch of engineering where you need to visualise the thing you are making, be your own draftsman, either pencil and paper, or computer. Then your own metallurgist, sorting the right materials for the job, then get out and get the stuff, castings, bar stock what ever. Only now do we start putting things together. This is my way as I design, and build my hot air/Stirling Engines from scratch.

I did delve into the wonders of Stuart Tuner with the restoration/rebuild of an S9, unlike the Stirling engines that are a mix of imperial, and metric measurements, the S9 was all imperial. Ian S C

[Neil WyattModerator @neilwyatt]

> I know how quickly they could be redrawn.

A fair point, but I was suggesting that the Stuart drawings need to be redesigned, not simply redrawn.

Neil

[nigel jones 5Participant @nigeljones5]

I started new into ME about 10 years ago having only ever used metric my whole life – I went down the route of converting everything only to find that I much prefer imperial now used to it and dont like using metric. Give it a go, its much nicer to work with IMO

[Steve WithnellParticipant @stevewithnell34426]

My workshop is all metric, I do have some imperial slot drills and jobbers.

 

I'm on my second Stuart Model and the conversion isn't a problem. Excel will produce a chart tailored to the users short sightedness, which can be laminated and becomes extremely long lived.

I usually have a calculator to hand too. I just don't find the conversion an issue.

I have a similar chart which is fractional inches to decimal inches,  but never used it.

Steve

Edited By Steve Withnell on 31/07/2014 21:31:09

Edited By Steve Withnell on 31/07/2014 21:31:34

[Stephen BensonParticipant @stephenbenson75261]

That is good to hear the castings must be flying off the shelves at Stuart Models with all their customers perfectly happy to convert their drawings dimensions to decimal imperial, does not follow any business model I am familiar with but I am pleased to be proved wrong.

[John OlsenParticipant @johnolsen79199]

Well, they have been selling them that way since about 1898 so they must be doing something right.

I think Imperial fractions are daft myself, but I wouldn't let that stop me making something I liked.

John

[Nick_GParticipant @nick_g]

.

This :- (iPhone app or similar)

Plus :-

Plus :-

Plus :-

Half an hour with the drawing and it was all sorted for my Stuart James Coombes. While doing it I was familiarising myself with the general layout of the engine, which I imagine is time most people spend anyway.!

Nick

[Neil WyattModerator @neilwyatt]

I think we are missing the point. Stephen isn't asking HOW he just can't understand WHY Stuart don't revise their drawings.

Neil

[Nick_GParticipant @nick_g]

Posted by Neil Wyatt on 01/08/2014 11:15:03:

I think we are missing the point. Stephen isn't asking HOW he just can't understand WHY Stuart don't revise their drawings.

Neil

Fair point Neil.

Perhaps someone should email them a link to this thread.?

Nick

[Roderick JenkinsParticipant @roderickjenkins93242]

I don't suppose there is great demand. As Neil has said, the engines would have to be re-designed, not just re-drawn. Although it is great to see a few contributors to the various forums from continental Europe, it is clear that Model Engineering is largely confined to the English speaking world and of those the majority are in GB and the USA. I would bet that the overwhelming majority of lathes in UK home workshops are imperial, even more so in the US and these must surely be the biggest markets for Stuart. Metric fasteners in model sizes are still a niche market for the model engineering suppliers.

I am sure it would be forward thinking of Stuart to provide their kits in either Metric or Imperial form but the history of Stuart and the likes of Reeves show that being a model engineering supplier is a precarious business. The business risk involved in dual offerings would be considerable.

That's my take on it anyway.

Cheers,

Rod

[JasonBModerator @jasonb]

It would not end with just the engine being metrificated, they would then have to stock a range of metric (fine)threaded steam fittings, fixings and carry suitable barstock to make up the kits. This all ties up capital and needs to be stored somewhere.

Personally I'd rather see any investment put into reintroducing some of the discontinued casting sets and updating any patterns/moulds so we have a bit of metal to machine off the castings.

J

[Stuart BridgerParticipant @stuartbridger82290]

My Stuart 10V drawing are covered in pencil conversions from fractions to decimal. An annoyance yes, major issue not really. As for metric, don't see the need. I can quite happily work in either metric or imperial. Have to say that I am happier with the latter. I learned metric at School in the '70s only have to learn imperial when I started in the aircraft industry in the '80s.

[Stephen BensonParticipant @stephenbenson75261]

The issue was never the fact that the drawings were in imperial the problem for me was that fact that they are all in fractions and incremental.

It would very easy to lose the fractions and replace them with imperial decimal almost every customer has to do this for themselves as evidenced by this thread I would guess very few mark out the castings as the designer intended.

Slightly harder would be to make the dimensions come from a common datum I agree to make them metric would be impractical without a redesign but the longer they put this off the more customers they will lose in my opinion as already mentioned Stuarts are largely ignored by Continental Europe and of course the biggest new market is China which has always been metric.

Edited By Stephen Benson on 01/08/2014 12:34:41

[JasonBModerator @jasonb]

Posted by Stephen Benson on 01/08/2014 12:30:27:

It would very easy to lose the fractions and replace them with imperial decimal almost every customer has to do this for themselves as evidenced by this thread I would guess very few mark out the castings as the designer intended.

 

I think a lot would mark them out as the designer intended given that the 10 range is aimed at the beginner who like me when I made my 10V only had a ruler, scriber, odd legs and simple homemade surface gauge and school made tri-square. A single datum is fine if you are using a mill or dro but does not make much difference if doing it all on the lathe.

J

Edited By JasonB on 01/08/2014 12:45:25

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Gordon W on 30/07/2014 11:59:50:

What scale would a 5" loco be in metric dimns?

.

(a) The same scale as it would be in any other dimensions

(b) 127mm

MichaelG.

[Neil WyattModerator @neilwyatt]

I have had a response from Stuart Models. Currently all their drawings are imperial, but they are actively looking at producing metric drawings. They will let me know if and when this happens.

In my view simply converting the measurements to millimetres is pointless. telling a beginner (or even an experienced builder) to make things 6.35mm diameter or 15.88mm long is just spurious complexity. Far better to convert to sensible metric sizes that reflect the level of accuracy needed, but this does require working through all the dependencies and prevents the revision of drawings being a trivial exercise.

Neil

[Steve WithnellParticipant @stevewithnell34426]

Like the ME drawing for the Whittle V8 crank that has the journal diameters marked up as 0.21875 inch? instead of the much less scary 7/32 inch?

Steve

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 01/08/2014 19:52:00:

… In my view simply converting the measurements to millimetres is pointless. telling a beginner (or even an experienced builder) to make things 6.35mm diameter or 15.88mm long is just spurious complexity. Far better to convert to sensible metric sizes that reflect the level of accuracy needed, but this does require working through all the dependencies and prevents the revision of drawings being a trivial exercise.

.

Well said, Neil

Sensible metric sizes are easily generated if you use the "pretend the conversion factor is 256" approach, that Ady1 and I have both encouraged. … A few dimensions may need tweaking, but I bet it would cover a good 80% of the dimensions in a typical Stuart model.

The metric version of the engine would be very slightly smaller than the Imperial one, but would have the same proportions..

MichaelG.

[Neil WyattModerator @neilwyatt]

> very slightly smaller

Bigger surely.

1/4" becomes 25.6/4 = 6.4mm instead of 6.35mm

Still awkward sizes, if I was doing it I would, as far as is reasonable, round all the dimensions to a whole mm (or half mm for small dimensions e.g. 1/16" – 1.5mm) and use metric bar stock for crankshaft, piston rod etc.

This approach would mean any given imperial dimension might translate to more than one metric dimension, in the interest of making sure it all fitted together, so the proportions would change very slightly.

Neil

P.S. The real beauty of the imperial system is the way it lends itself to both convenient subdivisions of larger assemblies and to elegant proportion. The Metric system offers potential for even better proportioning using Renard numbers (as applied to metric fixings – R10" series of 1, 1.2, 1.5, 2, 2.5, 3, 4, 5, 6, 8). Unfortunately Renard numbers can sum to Renard numbers from more complex or even no Renard series, 1.5+1.2=2.7. This is unlike fractions which never sum to fractions with a larger denominator. This is why fractions are so convenient for designing, once you are comfortable with them.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 01/08/2014 21:47:21:

> very slightly smaller

Bigger surely.

1/4" becomes 25.6/4 = 6.4mm instead of 6.35mm

Still awkward sizes,

.

Neil,

Forgive me that error … it's been a very long day: we were up at 5am to get my wife to the hospital for a difficult tooth extraction … then spent six and a half hours in various wating rooms, before she got to theatre!

I do disagree though, regarding "awkward sizes" … Tenths of a millimetre seem very convenient to me.

MichaelG.

[JasonBModerator @jasonb]

But who would want to turn a stainless piston rod to 6.4mm from the next size up nominal stock and even then you would not find a M6.4 die to fit it. A true metric version would use 6.0mm stock that could be threaded M6.

The 256 method is fine for lengths but just does not work on most diameters as threads, reamers and available stock sizes are not available in tenths.

And the other issue with the 256 method on Stuart castings is that the slightly larger sizes would leave you even less material to clean up the casting

J

[Michael GilliganParticipant @michaelgilligan61133]

O.K. … I will leave you to it.

MichaelG.

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