Anyone do pattern drafting??


    --Got a situation where I need to cast a small 3-cylinder engine block. Trouble is, altho I have drawings for the engine I'm damned if I can visualize what the patterns need to look like, to do the crankcase, etc. Would like to chat with anyone skilled in this, particularly if they live around the San Francisco Bay Area..     --Thanks,
--
"Steamboat Ed" Haas : Whatever happened
Hacking the Trailing Edge! : to Tom Nelson?
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I have a few questions and one assumes you have casting experience and a well equiped machine shop suitable for engine work:
1- What material will you cast into the mold? Iron, alumninum, what? Because you will want to get the correct 'shrink' rule to start making the pattern pieces. This is mostly important if you plan to use existing parts like pistons, crank, cam.
2- Is the engine liquid cooled? Because you need to provide for a water jacket between the cylinders and outer block, and developing these core pieces is the tricky part. You also have to find a way to suspend them in the mold cavity as you pour the metal.
An easy visualization would be to look at an existing block and trace the parting lines. This will give you an idea of how many sections were used to cast the part. Pay attention to the position of the steel plugs (blow, frost, heater hole, core, pick a name). These are the core pattern suspension holes.
The real tricky part is in the "one off" machining to accomodate existing crank, pistons, rods, covers, etc. Not trying to discourage you, but you will be developing this one casting and recasting it many times to get it mostly right.
Try making the engine out of plywood/hardwood and lots of glue. Use the same thickness you want the engine/cylinder walls to be. If its water cooled, leave a cavity betweeen the cylinder and outer block. Cut out any 'cast in place' holes and glue on any bracing or 'spuds' for mounting bolt holes. Then bandsaw it apart at the corners (like a productuion engine was - look for the parting lines). From this you create your pattern and then the mold.
I'd be interested to see where you are going with this.
Pete
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snipped-for-privacy@mts.net wrote:

can't find a good small iron foundry. Have done aluminum at home, but would prefer, in this instance, to farm it out to a pro shop.
>2- Is the engine liquid cooled?     --It's a steam engine; single-acting poppet valve variety; no cooling channels required. If anything I want it to run hot.

make a few spares, as I suspect I'll be beating these things to death..

eludes me..

inventing ways of making sealing wax; I'm wanting to build the fastest steamboat in the world. The record is one of the lowest on the books. A pal in Australia has the fastest steamboat currently floating; he did around 35mph about a decade ago. Rumor has it there's a team in Italy working on a boat. I'm just another crackpot with a dream, heh.
--
"Steamboat Ed" Haas : Whatever happened
Hacking the Trailing Edge! : to Tom Nelson?
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think in terms of the crankcase layout, first get the crank mocked up (out of wood is still good - assumes you don't have one) . Then cut out a large enuff hole in another piece of wood, split that in two to get two half circles, and bolt it back to gether around the crank. Do the same with your method of moving the valves and add that to the 'crankcase'. Now box in the 'crankcase'.
It occurs to me that steam engines leak past the piston seals quite badly (also not a big deal most of the time). If you intend to run the crank in oil and the crankcase is attached to the cylinder walls, can you calculate how long the engine will run before seizing up from the ensuing oil/water sludge?
Pete
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The application is way above my pay grade - but when I design cast parts my best resource is my casting shop. Usually I can just draw what I want my rough cast part to look like and they design the molds using techniques that they are used to using. I suggest you select one or more casting shops first, pick their brains as much as they will allow, then design your parts. Be prepared to adjust your design to fit their requirements, probably multiple times. They will design and build the molds. Who actually owns the mold is a point of negotiation. -- ******** Bill Pounds http://www.billpounds.com
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