C-612 Horizontal Steam Engine

[Jasonb]

No wonder you could not find it, all that stock has imperial sizes written on the ends or lables which you don't understand and none says 12.7mm.

Surprised you have not weighed it all in for scrap yet and got some proper metric sizes

[Jo]

No wonder you could not find it, all that stock has imperial sizes written on the ends or lables which you don't understand and none says 12.7mm.

That was a free donation from an old friend 

Surprised you have not weighed it all in for scrap yet and got some proper metric sizes

When I take off the brown protective coating I find metric sizes underneath 

Jo

[Jo]

Nothing exciting made today  Just the guide bars and their spacers.

I did find a suitable piece of metal coated with a brown substance that is just the right size for the crosshead 

Jo

[Jo]

On to the connecting rod: Jig time 

Having found a suitable very expensive piece of scrap-bin-i-um  tow holes were drilled and tapped M6 so that I could use the clamps from the BCA on this jig  Now it is time to mount the connecting rod on the jig, supporting under the length while clamping because bronze is soft and horrible to work with and to use a pointer to centre the rod on the jig so that hopefully the excess on the casting is evenly distributed either side of the two holes on the rod.

Now that the rod is square to the jig it can be up ended two holes drilled 3.1mm in the bottom and 3.6mm in the to for the big end bolts and the cap cut off with a slitting saw. Now the lower 3.1mm holes can be tapped 4BA.

The small end can be drilled and reamed and a suitable bush and bolt put through it to help with securing it to the jig. Then the big end can be bored 12.7mm. Sadly on boring there was an intrusion in the casting so that had to be dealt with by using some white metal and re-reaming the big end.

The connecting rod can now be bolted back on the jig through the big end and the small ends and the two edges either side of the big end milled to 25.4mm wide equally around the big end.

I am now ready to go for the next stage of the connecting rod 

Jo

[Roger B]

Was bronze a common material for connecting rods? Several ETW engines used it but it seems rather heavy and difficult to balance out 

[Jo]

Yes on early engines bronze was common. Grades of Aluminium alloys suitable for connecting did not come about until the 1930's and was rather expensive. On models if you put a set of patterns in for casting in the early days there was a risk that your connecting rods would be cast in the same metal as the crank cases  by having them cast in Bronze you knew they were good.



It is a bit hot today and the garden was more interesting that the work shop    I did how ever finish off the connecting rod. I tried clamping it to the jig but was concerned that because bronze has a nasty habit of warping  the rod may get out of shape so I decided to turn the ends to thickness. The central area of the rod is 8mm thick and the bosses on the end stick out 2.35mm either side. As you can see the rod is rather long and I had to be careful not to hit the rod on the saddle 

I then used the rotary table to take off the excess on the big end to give it the curve before finishing with a bit of hand filing and using some buttons for the small end. the small end outside diameter may still need to come down a bit more 

I need a crosshead before I can decide 

Jo

[Jasonb]

Roger a couple of other reasons that bronze gets used on models, not common on full size though:

- does not require separate bearing shells so overall size can be kept small

- unlikely to chill which is a risk with the thin sections if the rod were cast in iron so easy to machine.

I usually find the bronze used on American engines a bit harder than the soft gunmetal that gets used over here

[Jo]

If a rod was made in cast Iron there would be a high chance it would snap: Cast Iron has good compression strength but not so good expansion strength  A Forged steel rod is a possibility 


This bronze rod was just like the UK bronze: soft, sticky and grabby

Jo

[Elam Works]

I did find a suitable piece of metal coated with a brown substance...

Marmite? 

-Doug

[Jasonb]

I've a few models with cast DUCTILE iron conrods, seem to run OK, makes good crankshafts and axles too

[crueby]

If a rod was made in cast Iron there would be a high chance it would snap: Cast Iron has good compression strength but not so good expansion strength  A Forged steel rod is a possibility 


This bronze rod was just like the UK bronze: soft, sticky and grabby

Jo

I've used Bearing bronze (C660 or 932) for parts like that, very nice to machine. Some of the phosphor bronzes can be a real shop-gnome to machine.

[Jasonb]

Any more progress on this one? If you don't get something done its unlikely you will be allowed a fondle tomorrow night

[Jo]

Any more progress on this one?

Yes, but I am saving it up so it is worth posting 

Jo

[Jo]

The crosshead came out of a piece of brown coated second hand metal, thankfully the oxide layer came off easily with a rub on some emery. I have not shown any photos of the machining as it is much the same as doing the valve which I am coming to in a mo. The important thing with the crosshead  is the stepped in piece needed to leave 25.4mm to run up and down inside the bars and 9.53mm to run in between. I did not like the idea of having a pin through it and the connecting rod I much prefer something with a head and a pin/nut to prevent it from moving but as you can see when the engine is at bottom dead centre the pin is between the two guide bar spacers so there is no space for the pin to have a head 

The valve is a much more interesting piece to machine up: As with all of the Lancer castings this one is really close to size and I only had 0.5mm to take off on the two sides to bring it to 19.05mm  I decided to make the valve 38.1mm long with a pocket 16mm wide and 20.63mm long. The pocket is 4mm deep which is the same depth as the cylinder ports are wide to allow it to pass the same volume of steam/air.

Only once the bottom is machined flat and the pocket done can the correct height of 12.7mm be measured off to drill the clearance plus a little wiggle space for the valve rod hole be drilled. The last part of the machining is to mill a 4.76mm slot for the valve nut. The valve nut itself is a piece of square brass with a 2BA thread in the centre which had 1.6mm taken off the bottom and then the top rounded over to provide more steam/air flow.

Jo

[Jo]

We can now fit the valve into the steam chest. The observant amongst you will notice that other than the top and bottom all surfaces are tapered  So this means it must be clamped down to a jig. I have various pieces of come-in-handium-for a-jig but they all seem to be looking more like swiss cheese every day  It has now got to the point where I have to mark the holes I have just drilled so I can find them to tap them.

With the valve chest handle able it was up ended and the hole for the valve rod drilled and reamed 4.76mm and a hole drilled so I could tap it 3/8 by 32 ME later. The lump of casting around the gland hole had to be shaped by hand and then built up on one side with JB Weld as it was out of line with the casting 

Back to the jig and standing on its outer surface the inner face was milled smooth to allow the valve to fit and move easily without too much rubbing (0.2mm clearance). So I now have a set of parts for the steam chest 

There does not seem to be many castings left  I feel some negotiations need to be started tonight 

Jo