Julius 1" Metric Minnie

Hi All I am building Julius Metric Minnie traction engine and it calls for a 67mm od and a 63mm id copper tube with a 2mm wall thickness. Can i roll a tube and have a riveted seam or it a no no.

Thanks Kevin

Yes you can; it's a very common method. 2.5/8" x 14SWG might be obtainable...

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Best talk with your boiler inspector as he will have the last say and may want to derate the pressure due to the joint. I don't know if Julius' design has ever had any approval so best get the inspector to look over the whole thing before you buy any metal as there are a lot of deviations from Mason's original design and it will need updating to separate the manifold feeds. Plus the fact you could never assemble the engine as he's drawn it.

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An overlap joint gives problems with front tube plate and front firebox plate. Consider a strap joint. The rivets are only to hold it while soldering - the strength comes from the solder. Time was people used a castellated joint but I don't know if that is allowed now,

There is no reason for a boiler inspector to reject thicker-walled tube or firebox plates for the same designed working-pressure, if that overcomes material-availability problems. (Using thinner than specified would obviously be a no-no, at least not without careful analysis proving no significant reduction in safety.)

Beware though - although thicker-walled tube would take higher internal pressure, it is not a reason for raising the working pressure for a particular boiler, without reviewing the entire design to assess that proposal.

Such changes might need dimensional revisions elsewhere on a traction-engine, as the boiler is also the engine-frame, transmission-casing and vehicle chassis - but note my point above about strength. The boiler on a loco and many steam-wagons is supported individually on a separate, strong chassis; but a TE boiler is the chassis, and subject to large bending-stresses.

Separating the feeds from the manifold and putting their bronze or gun-metal bushes in the normal places in the barrel, should please rather than upset a boiler inspector, too.

Whether as Jason says, the Julius design is not mechanically practical, is another matter, but his questioning its boiler design having ever been "approved" is interesting. Outside of the requirements placed on commercial boiler-makers, have any of even our best-known and long-standing, published designs been "approved"? I would say so, but by accumulated experience and proven repeatability.

BR are you sure that is 3mm wall and not 76mm x 3m long plumbing tube which only has 1.2mm wall thickness and may not be C106 as I can't see any 3mm wall on e-bay. Yes thicker tube would be OK if other items are adjusted to suit.

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I've edited the post.

67 x 2.0mm wall is available as that is table "Y" thickness but not so readily available and you would likely have to buy a 3metre length, 1m if you are lucky. The usual plumbing thicknesses are known as Table "X"

Hi thanks for the coms i have looked around for a 2mm wall I did find 67mm od on eBay i and 250mm long for £20.00 am awaiting a massage back on the gauge

Kevin

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The imperial 2.5" tube which is the correct size for the imperial 1" minnie is available from most of the usual ME suppliers. Julius design for the metric one had a stock metric size picked off a chart somewhere with little thought to availability as table Y is not used that much.

Has anyone been able to find a working pressure specified anywhere on Julius' drawings?

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As I said in my first reply I don't know if any boilers made to the metric design have been made and presented to a boiler inspector, it is in effect a new design yet with not even a working pressure on the drawings it's hard to say what it's design is to be tested to. So anyone contemplating this design should seek the advice of their inspector before buying metal.

I don't think many UK inspectors would take too kindly to the stainless steel spacers used for the firebox stays and the threaded firebox stay method is dated now, the bolts shown retaining the cylinder are an impossibility, etc

Gear sizes are also seem interesting being a rounded up metric PCD and OD of DP sizes rather than converted to MOD1.25 and if you bend all the rear spokes the same as shown you will get a nasty looking wheel as can be seen in the GA drawings.

Edited By JasonB on 25/12/2020 20:51:55

Hi Jason you have looked at the drawings then, so you have helped me to abandon the metric version so i will get some tried and tested drawings from Reeves in the new year

thank you i think this thread has ended

A big thank you for all your help

Kevin

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If you have the book it can be done from that without the drawings, how mine was made many moons ago. The book is basically a reprint of the ME series and the mags can be found in the depths of the forum files, just change the last number of the url to get the next mag.

Worth looking at the three suppliers of castings as prices vary and some stock items that the others don't, as well as Reeves and Blackgates already mentioned GS Models do a fair number of items.

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Kevin I have sent you a PM

Roy