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[gondolier88]

Stuart D10- was going to be built to the plan, but decided I can build a better marine steam engine by changing a few things.

Mainly, the bedplate mechanically- i've scrapped the cast iron one and fabricated (still under construction) a new one out of brass and copper. It will sit a lot flusher to the engine bearers in the hull, saving vertical space and lowering COG. I've also designed and machined some new larger main bearings which should improve their longevity and I feel ST engines never have decent bearings anyway in comparison to old engine designs.

I will also be cladding the cylinders in brass not aluminium, and have already converted the valve chest covers from ST logo'd cast iron, to polished brass.

One side of the engine is 80% finished, but I knackered the other cylinder (first one i'd ever machined so hey!) and havn't bought a new one yet.

Really enjoying building my first engine and finding solutions to problems i'm coming up against.

Greg

Ps- if your wondering, no I havn't cleaned off the solder marks yet- i'm not leaving it like that!!!!1

[benjaml1]

Nice work.... 

[MONAHAN STEAM MODELS]

It's looking good!

[kiwimodeller]

Greg, a friend recently bought a box of bits at a swap meet and included was what we were told was a Stuart Ten cylinder and some other small bits. The story was that the rest was thrown out during a clean up of a deceased estate. He was mainly interested in the selection of B A screws etc so I am sure he would be happy to sell it at a very reasonable price to recoup some of what he paid. I will ask tomorrow and if so will take some photos and measurements so you can establish if it is the right thing. Cheers, Ian.

[SteamboatPhil]

Greg, I have a spare 10 cylinder  (I have about 20 of the things actually) if you would like one, I might also have the casting for the marine flywheel if I can find it, your more than welcome to that as well.
Glad you threw away the Stuart bearings (they're rubbish) I also build up my own con rod and cross head as well.

[benjaml1]

Looks like a nice crankshaft on e-bay right now for a D10....

[John W E]

Hi there all you steamheads

Here is a question for your experts.        Greg is making the bed plate from brass - will this not effect the tolerances on the main bearings, due to the fact that it has a different expansion rate compared to the rest of the cast iron parts - and also the crank. So will this not become a problem as the engine warms up?  Will it not seize up?  just a thought you see and an empty brain.....aye
john e
bluebird

[gondolier88]

Hi Benjam1,

Because i've enlarged the bearings and re-designed the bedplate to save space the distance between the centre 90deg webs is less now, what a shame because it looks nicely made- the webs aren't radiused on the bottom however- thankyou very much for the tip off though.

Bluebird,

Because i've made the bearings larger they shouldn't need to be as tight because they have a larger surface area- this will mean the shaft has a slight latteral movement along it's length.

Another thing i've changed due to differential expansion are the pistons! Yes, ST spec' brass for the pistons in a CI cylinder! So i've changed them for CI too!!!

Another reason i'm not overly worried about the shaft- if there are D10's alover wearing themselves away with brass pistons i'm sur emine will be fine.

Greg

[derekwarner]

bluebird....far from an expert....I have copied the following table from a GOOGLE search & whilst we see the relationship numbers betwen brass & steel....the simple fact is the temperature gradient variance in a model steam engine is say [125-50=75 degrees C]

What we mean here is the cylinders may get to 125 degrees C.....but due to cooling from the atmosphere & heat loss....through the legs down to the base where it would be lucky to see 50 degrees c

To further assist...we have diametrical clearances between the crank shaft journals & the bearing 1/2 blocks............a typical clearance here in a model application would be 0.001" > 0.002" ...

The important part here is to ensure that the base plate is truly flat so when the sub components are bolted individually they sit squarely....so in all I am sure the brass base would be OK...... ....Derek

Substance   Coefficient of linear expansion
Aluminum   23.0 x 10-6/°C
Brass   18.9 x 10-6/°C
Copper   16.8 x 10-6/°C
Iron   11.4 x 10-6/°C
Lead   29.4 x 10-6/°C
Nickel   12.8 x 10-6/°C
Silver   18.8 x 10-6/°C
Steel   13.2 x 10-6/°C
Tin   26.9 x 10-6/°C
Zinc   26.3 x 10-6/°C

Coefficients of linear expansion for various metals.

[HS93 (RIP)]

if all else fails Cheat  

http://cgi.ebay.co.uk/Crankshaft-for-Stuart-Turner-Steam-Engines_W0QQitemZ190361304695QQcmdZViewItemQQptZUK_Trains_Railway_Models?hash=item2c526afe77


     peter  

[derekwarner]

Peter...I am sure it may be an optical illusion  ....but if the webs toward the left are sitting flat in the horizontal plane....why are the webs to the right appear approx 3 degrees off the vertical?

It should not matter that it is a created isometric view...we were all taught the difference between horizontal & vertical was 90 degrees  .......not 87 degrees  .....Derek

[HS93 (RIP)]

Sorry Derek you're wrong it is only 87.5deg     so it's OK, you have to remember the curvature of the earth comes in to play between hear and where you are. 
 
         Peter   

[derekwarner]

mmmmm ...sorry Peter  ...[90 - 87.5 degrees = 2.5 degrees  ...ie 2.5 degrees off axis]

Any good reference will confirm that greater than 1.25 degrees of angularity off set....[with conventional tolerancing] could cause a twin cylinder model steam engine [irrespective of design] not to neceresally self start    ...Derek

[benjaml1]

Hi there all you steamheads

Here is a question for your experts.        Greg is making the bed plate from brass - will this not effect the tolerances on the main bearings, due to the fact that it has a different expansion rate compared to the rest of the cast iron parts - and also the crank. So will this not become a problem as the engine warms up?  Will it not seize up?  just a thought you see and an empty brain.....aye
john e
bluebird

Majority of the expansion would be in the horizontal plane so as long as there is sufficient end play I don't see a problem .....

[Patternmaker]

Having gone to the trouble of beefing up the bearings why not Machine a crankshaft with a larger dia main shaft, big ends & balance webs there is plenty of material in the con rods & eccentrics for a larger dia crankshaft.
As you are not using a flywheel this would this not make a smoother running engine.

Mick

[gondolier88]

Hi Mick,

That's a very good suggestion, and something I hadn't thought of. It would also make for a more contemporary look to the shaft which would of course have been balanced in full size- it would also allow the eccentrics to be machined onto the shaft rather than separately with a grub screw- I'll draw it up and see what comes out, but I think I may just go with what you suggest, thanks.

There isn't much work on the engine going on at the moment- my three jaw chuck is useless for all but the very roughest of work, and I'm waiting for the cash for a four jaw independant and a new three jaw chuck.

With your expertise perhaps you could suggest a suitable material for the shaft to be machined out of- would mild steel be best, or as it's running in brass bearings perhaps bronze might be a good idea?

Greg

Greg

[Patternmaker]

Greg,

I used 1" Dia ENiA Steel on my 10V, hard but machines well.
I will also do the same on Stuart twin launch engine, including the eccentrics.

Mick

[gondolier88]

Thanks Mick, steel it is then.

Have you started on the twin launch yet?

Greg

[Patternmaker]

I should get the castings this week.

Mick