Steam Cylinder Patternmaking

[Johnlanark]

By the way google books has lots of 19th century patternmaking books available. Joseph Horner has good steam engine information.

http://www.archive.org/search.php?query ... nmaking%22
John

[farmerden]

Thanks ever so much John. I've downloaded the book to my "favorites" part in my computer so if I disappear for weeks at a time I'm just over there reading this book! Anything you ever wanted to know about casting is there isn't it? I was thrilled to see that even the individual pieces of wood were laid out in the patterns so even I should be able to assemble a pattern. I can see i should have been cloned because one of me is never going to be able to do everything! But as they say it's not the destination as much as the journey and it looks like I'll have many more journeys to do. Den

[Johnlanark]

Today I continued with the cylinder patterns
- adding segments each end of the valve chest face to give cover over the steam ports.
- adding a reinforcing band to match the vintage engine. I used strips of kitchen mopping up sponge cloth, tacked on with superglue and then impregnated with resin to fully bind and harden. Not a technique you will find in the 19th century books!
- adding a 4 degree tapered exhaust core print glued over a pin.
- using filler to form fillets and fair off generally.



- drilling three holes on the valve chest centreline to take the gluing spigots of split core prints. I did this on my milling machine, using the DRO for accurate location. The core prints will be made in a similar way as the boss on the valve chest.



In between times, I've been working on the core boxes too. I made the main bore core box by staving as shown on an earlier post. It's only necessary to make a half core box, as the foundry will make two and paste them together. Two slots are needed, for the steam port ends to locate into; I inverted the core box over the layout and marked the positions carefully, sawed out and inserted blocks the required quarter inch thick. These blocks will make slots in the sand core. The inside of the box was plastered with that "easy sand " car body filler, and the outside strengthened with glass tape and resin.









The exhaust core is shaped rather like the business end of a key. A rectangular tab through the valve chest, then a straight circular hole at right angles, ending in a tapered circular part to match the shape made in the sand by the print. Historic books show the core box as paired single pieces of wood, carved out by a very skilled person.



I aimed for the same end product in an easier way, building up mirror imaged pieces a bit at time on to ply. From left to right
- a starter block to take a locating pin
- the rectangular section, thinner by half the required finished height
- a rounded section taking the port out the cylinder
- a tapered section to match the print



Once these were glued down to the ply, I added
- a ply tongue with rounded front, to control the depth of the rectangular section and make sure there is plenty metal between the port and the main bore.
- a small 1/32" thick strip to reduce the height just where the port passes through the valve chest. This is machining allowance, so that the slot in the casting can be opened up to exact size by milling.



After a little filleting of corners, these two half boxes will be cut out and trimmed, one put on top of the other and two locating pins fitted.

The patterns are nearly finished. But now I'm going on holiday so it will be a couple of weeks before this thread is concluded. Hope someone is enjoying it. John

[Johnlanark]

Some workshop time today saw this cylinder pattern just about completed.

Three core prints are needed on the valve face, one for each of the steam ports and a larger one for the exhaust in the centre. Pairs of “teeth” were made by turning pieces of hardwood in the four jaw chuck, then sanding to shape. They have gluing spigots to fit the holes made earlier. This was a fiddly job in wood, and I think using alloy and machining it with the milling machine would be easier. They still need filed to give a slight taper away from the parting line.





The steam port core box was made at the same time, passing from job to job as glue joints dried. I made this as an open box with side walls. Sand will be pressed in and a trowel will be passed over the top surface to level it. This is called strickling.
First photo. The steam ports are 5/8” wide so pieces of hardwood were thicknessed to this size by facing across in the lathe, held in the four jaw chuck.
Second photo. The pieces were laid on the layout drawing and formed to the shape of the port left hand side. The inside corner will be curved by filleting - with hindsight, I should have done it at this stage to give sharp edges.
Third photo. The layout was photocopied and cut out on the right hand side of the port, to give a template. Two pieces of ply were cut to this shape. I made them too small at the bottom edge really.
Fourth photo. The ply pieces were glued to the sides of the wood, maintaining a ¼ “ distance to give the required port height.
Fifth photo. Two removable end pieces were fitted and located with holes and spare small allen keys that caught my eye at the bottom of my toolbox. Once the core sand is rammed up, probably with wires reinforcing it, the moulder will remove these pieces to help deliver the core out of the box. To give machining allowance where the port passes through the valve face, a piece of bank card was glued in at the base, and a corresponding notch filed in the top surface for the moulder to follow when strickling. With just 1/4" height there is not much reduction available for machining allowance.











The box is still to be tidied up and sanded, but is basically complete. I hope you can see how it will make an S-shaped sand core rectangular in section. Two of them are made for each cylinder. They fit into the top and bottom prints in the sand at the valve face, and the slots in the main bore core.

Turning to minor pieces now, the engine has two bronze glands, one for the piston rod and one for the valve rod. The castings will be machined all over. I made oval shapes oversize and thickness, and mounted them both on a round stick, with excess each end that I have a notion will help the workholding of the castings for machining. This pattern will be moulded with the parting line down the centre of the stick. The ovals are not tapered - for this short height I’m relying in the rapping of the pattern in the sand to free them. I started filleting but was distracted by a visitor and the filler partly hardened, hence the crumbly part finished look.





The finished piston is 7/8” thick. I made the pattern 1” thick by gluing two thicknesses of ½” ply together. This was then sawn and sanded round oversize, with taper all one way on the edge.



I have still to make the valve chest cover, but it will be a simple rectangle of plywood, oversize and over thickness for machining all over, and would make a very boring photograph.

That finishes the cylinder set, with just sanding and painting left to do. I’ll round off the thread by posting photos of the castings when received. I have a feeling that this detailed description may make it seem more laborious than it actually is - once you have the principles in your head, the woodwork goes quite quickly.

Cheers for now, John

[farmerden]

We're all out there ,John, enjoying your progress immensely.My only worry-Will there be a test at the end to see if we were really listening? Keep up the good work! Den

[Johnlanark]

Thanks for that. The only test is for me - whether the foundry will be able to mould the patterns OK!
John

[87gn@tahoe]

John,

Just wondering if there were any updates on this, or any of your other endeavors?

[Johnlanark]

Ah well, I was kind of hoping that question would not be raised! I posted the patterns off to a foundry I had not used before. They took ages to acknowledge receiving them and only after much prompting. A further long time time went by, to the extent that I forgot about them. On enquiry they eventually said they could not cast them and would send them back, but I never got them. I'm the first to admit that the patterns were kind of rough but they were only for a one-off and I've had this sort of pattern cast many times before. Normally I go to Laings Foundry in Edinburgh so I'll stick with them in future - no doubt to the relief of the the other place.

My Herreshoff boat, engine and the three drum watertube boiler were put on the back burner last spring when we bought a classic wooden yacht built in 1936. I wonder if the site filters will permit a picture of a s**ling boat? She needs a new engine, cockpit refit and lots of paint and overdue maintenance work. Hope to have done all this before too long and get back to finishing the new steamer. Forgiveness is sought from the Forumites for this regrettable deviation from the True Path. John.

[S. Weaver]

John:

Fear not - a number of us are heretics. For me the distinction is the conditions. I sail where I'd never take a launch and vice-versa. Also, there's the cracking of the sail, the smell of tarred marline, turpentine and all of that ...

[barts]

I use pine tar, linseed oil and turps on the wood work on the Otter - smells great! Some year I'll have a steam boat large enough to carry a small sailing dingy on the cabin roof .

- Bart