Rebuilt Bulleid West Country 3D CAD designed & mft in 3.5 in

[Oily Rag]

May 5, 2020 13:42:19 GMT Roger said:

Just a thought.... do you need a combustion chamber if you have three radiant superheaters?

R, as my dim mind currently understands, combustion chambers main purpose is as the name suggests, more room to ensure full combustion before the gases enter the tubes and flues. This is influenced by the vertical position of the grate to fit over the trailing wheels, fit the ash pan underneath and within the over all loading gauge restriction. Unable to have a deep enough fire box the only was to go forward. It would also increase the firebox radiant heating surface as well. I think I read it also helps with some types of coals with high amount of volatiles, lots of tests of the gases emitted at the stack to check combustion, monoxides etc ?

[masahiraoka]

Roger,

technically neither a combustion chamber nor radiant super heaters are necessary but i'm keen to eventually try to obtain the maximum power and efficiency possible hence also the 100 lb/sq in. boiler.

i've recently read an excellent book that discusses the pros and cons of all the elements that go towards locomotive power and efficiency, American Steam Locomotives, Design and Development 1880-1960 by William Withuhn. Withuhn was both long time transportation curator at the Smithsonian as well as a licensed locomotive engineer who drove dozens of engines. i thoroughly recommend it.

[Roger]

May 6, 2020 0:23:24 GMT masahiraoka said:

Roger,

technically neither a combustion chamber nor radiant super heaters are necessary but i'm keen to eventually try to obtain the maximum power and efficiency possible hence also the 100 lb/sq in. boiler.

i've recently read an excellent book that discusses the pros and cons of all the elements that go towards locomotive power and efficiency, American Steam Locomotives, Design and Development 1880-1960 by William Withuhn. Withuhn was both long time transportation curator at the Smithsonian as well as a licensed locomotive engineer who drove dozens of engines. i thoroughly recommend it.

Fair enough. I wouldn't have thought the efficiency would be much different without the combustion chamber unless what Daz suggests about combustion is a factor in our small scales.
I doubt if you will be short of power, even at 90PSI. If you go too high it will just want to keep slipping. I was advised against going to 100psi for that reason. If you've got a lot more power than you can put down onto the rails, it's not much use to you.

[uuu]

On boiler pressure: Ken Swan designed Bridget for 120 psi, but noted that careless drivers could "empty her firebox into the surrounding trees. The fireworks display was magnificent, but those watching ran for cover". Jessie is substantially the same loco, but is downrated to 100 psi.

Wilf

[stevep]

I may be wrong, but I always understood that most model boilers with a combustion chamber had them to shorten the length of the firetubes. There is some formula for the length and diameter ratio, and if they're too long, you have to make them a larger diameter, and then have less tubes.

By putting in the combustion chamber, the tubes could be shorter, resulting in keeping smaller diameter, and having more tubes.

[44767]

Apr 5, 2020 10:50:38 GMT Cro said:

Be careful with 3D printed stainless, metals in general, as they are extremely difficult to machine as the sintering process makes them very hard.

Above quote was truncated.

There were posts about this quite a while ago. The process used then was SLS (Selective Laser Sintering) which produces a porous structure of tiny balls of steel fused together. This part was then dipped in molten bronze to make it solid. It was this that I think made these parts virtually unmachinable. It is well known that when cutting stainless steel one must not let the tool dwell as it causes rubbing. This work hardens the surface very quickly and makes cutting further difficult. I think the soft bronze allows the steel balls to push away from the cut causing it to rub and so harden.

These brackets that Martyn has had done would have been done by SLM (Selective Laser Melting) this leaves a part which is solid metal with no porosity. The metal he's chosen is an austenitic stainless steel which cannot be hardened by heat treatment so it cannot be hard as delivered. It should be just like any 316 SS to machine. Like the data shows, use very sharp tools and things should be fine.

[masahiraoka]

Smokebox and Front End Plumbing

• The smoke box is of a 2/3 split design as shown in the screen shot and is typical of usual model engineering design except for -

• The supply side steam pipe-smokebox connectors in green, which will be 3D printed as will be the orange and red shaded cylinder exhaust pipes

[suctionhose]

Outside admission piston valves?

[masahiraoka]

Ross
yes we’re following full size practice on the rebuilt WC i.e. outside admission for the outside cylinders (as originally built) and inside admission on the inside cylinder, (which was a new cylinder purpose designed for the rebuild).
ciao martyn 

[masahiraoka]

To add some further feedback in response to various comments

1. Mike (44767) is correct, our brackets are being printed with the Selective Laser Melt process so producing “solid” stainless steel components.

2. re machining these components our project chief engineer Phil reminds me that we’ve successfully reamed these brackets with sharp (new) HSS machine reamers, using only an ordinary 38 year ‘old’ Taiwanese vertical single-phase ‘hobby’ mill with 3MT spindle.

that said we’re also trialing machining with carbide tooling.

I’ll post more material tomorrow

ciao martyn 

[masahiraoka]

Buffer Beam Outside Brackets

• The 3D CAD screen shot shows the three large brackets (in grey) that support the front buffer beam

• The manufacturing principle applied for these brackets was to use a flat sheet-folded design

• This photo shows the laser profile cut flat pattern development of one of the outside brackets

• The following photos show the finished folded and brazed outside brackets.

• This manufacturing strategy has proved to be complicated with regard to folding in exactly the required positions to obtain the necessary dimensions and "squareness". As a result of this we're planning to convert this design into a tab and slot type

• The moral of the story is that the construction of a full working prototype is informing further development of the 3D CAD design.

[Roger]

I've found that machining a former is a quick and easy way to get folds in the right place, using the holes with pins or edges to line it up perfectly before bending. You could always 3D print a former if you don't have the facilities to machine one.

[masahiraoka]

Roger

good suggestion which we could well trial after trying a tab and slot design.

martyn 

[Roger]

If you don't need fillets of Silver Solder on the joints, one idea is to TIG weld the tabs in the slots. I do this sometimes anyway to hold them in place for Silver Soldering. You don't need any filler wire, it takes seconds, and it's very strong.

[masahiraoka]

Here are some further closeups of the front end and valve gear

[Oily Rag]

May 11, 2020 7:39:36 GMT Roger said:

If you don't need fillets of Silver Solder on the joints, one idea is to TIG weld the tabs in the slots. I do this sometimes anyway to hold them in place for Silver Soldering. You don't need any filler wire, it takes seconds, and it's very strong.

One can TIG and silver over the top to get the fillets desired.

[masahiraoka]

Locomotive design as currently completed with and without boiler cladding

[Roger]

That's looking really good. Just bear in mind that with all the will in the world, your cladding won't fit precisely. that's because the boiler won't be to the drawing, however hard you try, and sheet metal work is fickle at the best of times. Just make sure there's enough wriggle room in the model so you're not in trouble when the boiler is a little big in places and the cladding won't fit. I certainly wouldn't make the cladding until the boiler is complete.

[chris vine]

Just to add to Roger's comment:

Be sure to allow a decent clearance between the spectacle plate and the outside of the boiler cladding - the paint thickness doesn't scale. And, if the cab isn't mounted on the boiler (as in 9f etc), the boiler will certainly try to expand through the spectacle plate and ruck up the paint...

Magnificent progress!

Chris.

[stevep]

May 18, 2020 8:32:58 GMT Roger said:

That's looking really good. Just bear in mind that with all the will in the world, your cladding won't fit precisely. that's because the boiler won't be to the drawing, however hard you try, and sheet metal work is fickle at the best of times. Just make sure there's enough wriggle room in the model so you're not in trouble when the boiler is a little big in places and the cladding won't fit. I certainly wouldn't make the cladding until the boiler is complete.

I remember, many years ago, when someone said something in Model Engineer about boiler making not being a precise art, they were taken to task by an eminent model engineer who had worked at Brighton works, where he said that the tolerance on the full size boilers was 1/64".

Some things don't scale.