Stuart D10 Metric Plans

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

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

(b) 127mm

MichaelG.

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

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

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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.

> 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.

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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.

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

O.K. ... I will leave you to it.

MichaelG.

Ouch, I hope she's feeling better now.

Neil

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Much better, thanks Neil.

MichaelG.

I don't really see the point of the "256" method. On my Stuart builds, I take the dimension off the plan, get the metric version from my chart, say 1.588, then do a sense check against the plan - is 1.6mm OK or is 1.5mm better?

So I think the 256 method blindly applied removes the sense check and I think it good for a beginner like me to be forced to think through the design as part of the learning. One thing I have discovered is that there are few critical dimensions. There is no pain in using a custom conversion chart, honestly.

I'm throwing in with Jason on the diameters piece. Except for the piston/cylinder bore dimensions (which is not part of J's argument). 1 inch is on the plan, but 25mm is perfectly fine (If you throw out the O-ring supplied which I don't like) . So again, you do not need to calculate the conversion. In any event, whatever dimension you end up with on the bore, you then have to turn the piston to a good fit, not to a measured dimension anyway.

Steve

Steve,

Just to clarify ... the 256 method works as a good way of producing convenient metric dimensions from something designed in fractional inches. [i.e. the results are suited to a machine, or marking-out regime, calibrated in decimal millimetres]

MichaelG.

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P.S.  ... I would never propose blindly applying any method  

Edited By Michael Gilligan on 02/08/2014 12:39:56

Sorry to resurrect such an old thread, but does anyone know if the game's moved on since 2014 please?

I have a metric scaled lathe, and I'd like to build metric if possible.

I'm ok with doing imperial/metric conversions, just thinking if I can get metric plans, then there's one less thing I'm going to screw up.

Thanks.

Edited By Tifa 8572 on 26/02/2021 10:43:46

I've come to the party a bit late BUT, IF the engine was designed in metric then castings Etc would also be metric and all would be simple. But starting with imperial castings and being a beginner trying to convert to metric could cause trouble ! If one can afford to buy a set of castings then the additional cost of a set of digital calipers which can read in both and convert is money well spent. Trying to work in both at the same time - unless you are used to doing so is a recipe for disaster

I believe there are digital calipers that will read in fractions ?

The booklet sold by stuart models " Building the vertical steam engine" by Andrew Smith gives dimensions in both disiplines. The threads are sudo metric being BA. Noel.

When I started, dwgs used fractions and decimals, the fractions indicated that the dimension could be made to a wider tolerance,the decimal dimensions indicated that lot closer tolerance was required, it was quite common for many companies not to have dwg tolerances in a indicated box at the bottom of the dwg,sometimes tight tolerances would be specified against individual dimensions.In earlier times dwgs would have notes "make to shop practice" or " "Bore to suit" ,"drill and ream "to a fraction dimension just indicated to the skilled man that a nice round ,smooth hole was required no tolerance given. These practices were ok when long established UK companies made everything in house, When companies started to use subcontract suppliers,or make items for or assemblies for say a government contract ,start to mass produce products where spares were required regularly then dwgs had to be specific regards tolerancing ,finish,material etc. Where I was first employed we were expected to turn the brass fittings of a microscope using fractional dims to within plus minus .005 of an inch or better using a steel rule.Diameters which were theaded were measured with a micrometer,When I went to my second job they used imperial decimal dwgs with tolerances specified and that did take some getting used to dont know why but I found that working to decimal imp and using a rule with tenth and 1/20 ths of an inch was awkward and slower.At a third company ,a USA based multinational ,they used decimal /imperial ,here I was an engineer involved in procuring subcontracted parts so never got really involved actually making parts,so did not find any problems,Metrication came along and again no real problem,as most of the scientific instruction at grammar school was in metric units,the science masters scornful comment one day on imperial units was "only engineers and plumbers use imperial units" In 30 years of retirement ,topping up the pension I took on any work both to imperial or metric units,despite having a fully metric lathe and another lathe with dual dials plus imp and metric mills I found that I was far quicker using imperial dimensions because my initial training was in imperial units and spent my first 6 years using them,and I just cannot see any need to convert a dwg from fractions to decimal, the conversion factor is just in my memory if I see say 3/16 ins I just know that its .1875 ins.

Noel -

Yes: most digital calipers and micrometers offer readings in both inches and mm, selected by a button; and some (not all) also give fractional-inch readings.

I have one of those Tracy Tools poster-sized conversion-charts in my workshop, hanging from a dress-hanger so I can turn it easily to read the tapping-drill charts on its reverse.

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The problem I have is not Imperial / Metric as such. It's with these blasted centimetres insisted on by the schools, rag-trade and natural-history radio programmes!

I know the cm is slightly more anthropocentric hence perhaps more comprehensible for everyday use like shopping, than those tiddly little millimetres; but I am used to both Imperial and proper metric units, at work and in my hobbies, so find it rather hard to grasp.

Usually I convert them to mm, knowing 200 of those is about 8" and a 19mm A/F spanner fits a 3/4" A/F nut.

The use of Inches and two-s scale fractions thereof in model-engineering is convenient for scaling from prototype, but does lead to awkward things like 17/64".

There are good and points in all measurements system, which are all artificial anyway; but if we are to work to metric units then yes, we should use sensible conversions, not always the arithmetical ones; and with due consideration of the consequences.

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I don't know that 256 factor. .That is new to me. I use 1 inch = 25.4mm then round if and as necessary; but let's think about that 17/64" fraction I gave, quite randomly.

17/64" = 0.265" = 6.75mm: so 6.5mm or 7mm.

Not much difference there, no; insignificant on many components. However even that tiny change like might have a significant effect on something like a wall thickness, the overall sizes of available ball-bearings, or the meshing of gears (or choice between imperial and metric gears).

Straight conversion and rounding might not always be as simple as first appears.

'

Incidentally, the BA system is not "pseudo-metric" as Noel says, but is metric though inch-described; with its full range by geometrical progression. Whilst not matching completely and none interchangeably, some of the common BA sizes do have M-series equivalents close enough for direct replacement without major re-designing. The accepted tapping-drill diameters for BA threads are quoted in mm to 0.1mm steps too, so are easily obtainable.

When I began machining for a living my first two workplaces were jobbing shops . It was the norm to be faced, on a daily basis with a variety of drawings (metric v imperial) from a variety of sources and a variety of machines to work with (metric v imperial) Sods law almost guaranteed that you would be working an imperial machine with a metric drawing or vice versa. Needless to say one did not round up nor down!

It quickly became the norm to convert - either way depending on machine set up - and work to the resulting dimension ie no rounding up or down as such (see next para) just the given dimension in it's 'opposite' form for the machine being used .

Still do that to this day. All metric machine movements save down feed on Linley mill. Current drawings being worked from are in fractions - e.g. 23 divided by 64 on a calculator gives .359375 x 25.4 = 9.128 (9.13 working dimension) No rounding to stock size either - just work to that dimension. Metric dimensions on imperial machine - just reverse that.

I usually begin a project, if it requires it, by sitting down with the drawings and a calculator and convert all dimensions anotating the drawing with red ink with the converted measurments.

A benefit of this is that sometimes errors are seen before machining.

As always it's horses for courses - it is not something I even give thought to anymore just do the conversions and start machining.

Of course if you have say a 3/8th reamed hole called then you ream it 3/8th but you make the part to fit 9.52mm.

Threads are a different matter - it's then down to individual choice - I still prefer to use BA and ME but there are occasions that metric are a suitable alternative.

Just my thoughts on this - I really don't see this as a problem as such - just work to the machine dials but of course you need to have both forms of measuring kit

Regards - Tug

The world has gone METRIC ? OH NO IT HASN'T !!!! I had a heated discussion witha builder I was doing all the structural steel for - He told me the building trade has been metric for decades ! I asked why in that case were some of the steel beams 254mm rather than 255 or 102 instead of 100, there was no intelligent answer. I pointed out that one was 10" to a tolerance he would not understand and the other was 4"

The commonest hydraulic fittings are BSP and cameras use whitworth. Noel.

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Pretending that 1” is 25.6mm not 25.4 is a convenient way of approximately converting between the binary series of fractional inches, and millimetres.

No more than that.

MichaelG.