Little and large - building 2 vertical steam engines.

[Gas_mantle]

Hi all,

While I decide how best to make the con rod I thought I'd have a go at making the exhaust gland, this is the first time I've dealt with castings so I could do with a bit of help. At the moment I have the cylinder block milled flat and drilled (the hole is central to the larger ellipse shape) at first I kind of assumed I only need to mill the smaller ellipse and make a brass gland to match but now I think I need to mill as far as the larger ellipse then make the gland to match that. Is this correct ?

If I do mill down to the larger profile is there any simple way of getting the gland to match, I can't see how I'd be able to machine the outer profile with the gland in place so I'm assuming it's a case of hand filing it ?



I'd be grateful for a bit of help, thanks 

[MJM460]

Hi Gas Mantle,

A great build, I have been following with interest.

First, a minor point of terminology, I suggest you are talking about flanges, a gland is the term generally applied to the soft packing arrangement which prevents leakage where a sliding or rotating shaft passes through the pressure wall.  The stem of a valve, your valve rod and piston rod are all sealed by a gland.

But to answer your question, as in full sized piping systems, you can do whichever you like.  Some flanges are smooth metal to metal, but most have a gasket which fills the microscopic irregularities of any surface if you look at it with high enough magnification.  Or you can machine grooves to confine an o-ring, perhaps in one side only.  You can even make loose flanges to use instead of nuts with the common tube tails.

The gasket has to be squeezed tightly between sufficiently smooth metal surfaces to ensure a seal, and that is the job of the bolts.

Low pressure piping gaskets are generally full face, which means they are the same outside size as the flange and have holes for the bolts and the flange has a flat surface to suit, but higher pressure systems have a smaller diameter raised face for the gasket face, which is totally inside the bolts so the gasket does not have bolt holes.  The smaller diameter of the raised face allows the bolts to create higher pressure over the gasket to squeeze it as required to seal against high pressure.  And the raised face on each flange plus the gasket thickness mean there is a small gap between the flanges at the bolt circle so the bolts can use the elasticity if the metal to slightly cup the flanges to apply maximum pressure to the gasket.  A frightening thought when the flanges are high tensile forged steel over an inch thick!

So make a raised circle around the steam passage (just inside the bolt holes) very smooth, make a simple washer shaped gasket from oiled thick brown paper or other thin gasket material, and squeeze the gasket between the flanges to make it pressure tight.  Or you can make a full elliptical smooth surface and make a full face gasket.

That is the full size practice, I will leave it to others to say what they find easiest to replicate in model sizes, but my observation is that most use the full face style.  I generally use nuts and tails, as small flanges are a bit fiddly.

MJM460

[MJM460]

Hi again Gas Mantle,

On thinking a bit further overnight, (it is now morning here), I realise that I should have added that the flat face design of flange is mainly used with cast iron flanges, so perhaps more in line with prototype for historical steam engines.  Because cast iron fails in a brittle manner, the bending of flange edges by bolt tension is not a good idea.  The full face gasket design makes the whole thing a compression joint, so less likely to crack the iron flanges.

On your specific question of detailing that casting, would it be possible to just machine the actual gasket sealing face and leave the outline as cast?  If the matching pipe flange is just slightly larger, the casting outline will hardly be visible.

From the model making point of view, I see the most difficult part as lining up the bolt holes in the matching pipe flange.  There is not much tolerance on orientation, so you need one of Chris's amazing soldering jigs to keep everything in place.  The flanges can be made square in the end of a tube by recessing the tube into a small socket on the back of the flange, but the orientation of the bolts is more difficult.  Alternatively use a tail type tube end with a loose flange to allow the flange bolt holes  to be rotated to suit.  A longer steam pipe with at least one right angle bend will also allow some little bending of the tube to line up the bolt holes.  Actually studs threaded full length are used in the industry I come from, rather than bolts, but the holes are still called bolt holes.

I hope a little information from full size is helpful.  I am looking forward to seeing what you decide.

MJM460

[Jasonb]

You don't really need to worry about shaping the flange to match the larger surface as the cleading will cover it and be cut to the flange's outer shape. I would mill down until the flange mounting face is flush with the edge of the port face which will give a nice flat surface for the cleading a shown in yellow. The current castings don't have the smaller raised oval shape that your older castings do.

Lining up stud holes should not be a problem if you build as per drawings and just screw the pipe into the flanges tapped hole. If you want to hard solder it then you will need to make sure it solders into the correct position.

Being bronze there is no risk of cracking the flange so you could add a recess for an O ring, or just use a thin paper or thinner still liquid gasget

[john mills]

if the faces are machined flat as jason says there should be no problems.on the engines i have built i have not
cut gaskets often not even liquid gaskets and don't have problems running on steam. liquid jointing would be good

[Gas_mantle]

Thanks guys, that's great. I must admit I hadn't considered milling down to the flat face but it makes sense now you mention it. I was kind of expecting to have to file a matching flange by hand but that seemed a bit of a messy way of going about things.

As for the con rod it seems from the plans that in a real Stuart engine it would be a single component made from brass (albeit with a split bearing), I think I'd rather make a steel version with separate brasses so intend to give that a go next then make the flange 

[Jasonb]

It is a soft gun metal casting, you will be better of with a steel one with split bronzes. Something like the Muncaster will do fine.

[Gas_mantle]

Thanks, something similar to the Muncaster is my intention. If there is one part of making steam engines I dread its the con rod / bearing assembly I always struggle but want to get it at least roughed out today.

[Gas_mantle]

I've being putting off making the con rod for a while but I'm not going to have a working engine without one so I've spent the last couple of days at it. In the past I've struggled with these components so I wasn't expecting miracles with this one 

To start off I silvered soldered matching brass blocks that will form the split bearings.



I'm wasn't sure if the trunk guide is slightly thicker than a proper Stuart casting but there doesn't appear to be a lot of room and it's not helping things that my crank pin at 12mm dia is slightly larger than the plans specify. Although I can partly use Fusion 360 I'm not yet sure how to use it to work out clearences so it's a bit of guesswork and hope for the best.



This block will be the bottom keeper and it is becoming apparent that increasing the crank pin dia to 12 mm isn't leaving much room to drill for the 5ba bolts.



I chose to drill the 3 components individually using a vice stop then use a spare drill bit to hold the parts ready to drill the 2nd hole in 1 go.





A centre was drilled in either end of the main part and the keeper.



A bit of milling to make room for temporary bolts.



Then drill and ream both holes at the same setting.



Mill away most of the waste to reduce the interrupted cutting in the lathe.



To turn the radiussed sides to the big end I made a temporary centre with recesses to enable the bolts to function as driving dogs



It was a bit of a crude set up but fine for the few small cut to round the sides.



A 12mm mandrel and a dab of Loctite 638 magic juice was used to hold the part for turning small raised rings.



That takes me to this stage, it's a bit narrower than I would of liked but I'm concerned about clearences.



Time to turn the rod taper.



So this is the part so far, with the keeper reduced in size and the taper cut the proportions look a bit better



At this point I decided to leave the maching of the top until I'd split the bearing and had a trial fit to check clearences.





Success, it fits and turns ok without fouling 





It's far from perfect but I reasonably happy and decided celebrate with a few pints of the dark stuff this evening. I'll finish it off and machine the crosshead over the weekend.

Hopefully in the next day or 2 I'll be in a position to see how well it turns with the parts so far operating together 

[Jo]

Well done Peter,

As with so many bits of engine they are rarely as difficult as we think they will be at the start 

Jo

[Gas_mantle]

Thanks Jo 

I guess it's all experience, this is the 4th of these con rods I've made and each one is slightly better than the last.

I'm really looking forward to seeing how it turns over, it's a fairly mundane sort of engine but quite a bit more powerful than anything I've built so far so I can't wait to get it running on the hot stuff 

[pgp001]

Hi Pete

That's starting to really take shape now, it looks a bit different to that random bit of scrap you bought at the last club auction 

Phil

[Gas_mantle]

Cheers Phil 

I'm quite pleased with how it's going, it will never be a thoroughbred Stuart but ought to be just as powerful. When you consider a full set of castings costs over £450 with postage and VAT but this will cost me about £70 then it has to be a bargain.

The club auction night is in a couple of weeks so I'll be on the look out for some more junk high quality merchandise.   

[Gas_mantle]

Well I'm happy to say I have now fished the con rod and crosshead assemblies and had chance to see how the engine so far aligns and turns over, I did take photos and decided to make a short video. The first video wasn't right to I deleted it from my camera along with my photos 

Anyway, things with the engine went fairly well and although I haven't yet made the crosshead pin or got a flywheel yet I have been able to see how it is shaping up.

I remade a second video so as there are no photos to show I thought I may as well show it :-

<a href="https://www.youtube.com/watch?v=OYfFRb9jkII" target="_blank">http://www.youtube.com/watch?v=OYfFRb9jkII</a>

[Gas_mantle]

The no4 is now starting to look like an engine with the flywheel now in place, firstly though I machined a couple of flanges to take the inlet and exhaust plumbing, I started out by turning 3 brass components as the 3rd will form the basis for the valve rod gland later.



A square of steel is then turned and threaded to become a mandrel to turn the parted of rear face and support the parts for later machining.



It's not that easy to assess the radius of the mating surface of the casting so it's a bit of guesswork making trial cuts with the boring head in the mill until I seem to be getting the correct profile. Using the mill in reverse with the boring head is far from ideal but with a bit of common sense and light cuts it can achieve the desired result.



Turning the block round to machine the other side it's starting to take shape



The likelihood is that I will machine away the raised boss on the casting as suggested in an earlier post but for now I've let it and I am machining the flange to match. It's slightly oversize here but still needs a bit of filing to round the ends.



Quite happy with these.



The square block serves as a holder for marking out then drilling.





With the flanges made it's on to the flywheel. I opted for a 5 curved spoke casting as this style has the wider diameter hub I need.



I guess we all have different techniques for tuning flywheels but for the benefit of other novices this is how I do it. Firstly hold in the chuck by the outer edge then get the inner rim running as true as the casting allows.



It's now possible to machine all the features on this side and part of the outer rim. Once happy with the turning I drill and ream for the 12mm shaft.



A close fitting 12mm arbour is turned and the wheel is turned over then locked in place with 638 green snake venom. Provided the arbour is a good fit it should run true enough to turn the remaining features. I'm not a big fan of these cheapie brazed carbide tools but cutting left to right this one seems to work well.



The arbor serves as a holding fixture to drill for a grub screw.



That now takes me to this point.







Starting to take shape 

<a href="https://www.youtube.com/watch?v=5DBwyGASjYc" target="_blank">http://www.youtube.com/watch?v=5DBwyGASjYc</a>

Hopefully within a week or 2 I'll be able to get it running :-)