A number of years ago I started on a 1/3 scale pocket valve Harley. I carved patterns and cast the crankcase conventionally in aluminum, and the flywheels in cast iron . I made knife and fork rods and dummy pistons from the solid so I could mock up the cylinders. My first set of cylinders were made in aluminum by stacking the wax fins fusing them together and then investing, burning out and pouring in a small chamber. When I moved on to the pocket and head I wasn't able to pull the silicon mold from the pattern due to the depth and dimension of the fins. One attempt with latex rubber failed due scorching the wooden pattern. I stalled out there and moved on to something else. These images were clawed back from photosuck, but I had started a thread over at AA. So after the experience I had with the brake calipers for the 9" Ford in the EDM I thought it was worth a try to pour a cast iron cylinder in the core molds like I used for the Indian heads and then use the EDM to cut the space between the fins.
I prepared the patterns by filling between the fins with modeling clay, then gave it a skin of shellac to harden. I made a frame from aluminum to hold the mold while the it is baking, then slip it up and dust with parting and cut the locator divots before ramming the cope. I had a corebox for the bore and pocket so I made multiples to cover the loss from breakage. Vents were cut in the cores and glued together with flour paste. and finally mounted in the mold. Then when I went out today, the mice had eaten one of my cores. They were after the flour, and maybe a little of the linseed oil. The intake above on the left is gone and they gnawed at the repair I had done on the bore. I set the water trap and rammed up more pocket cores.
Fixed the mold and rammed them up in a flask. I did not cut gates before ramming so I could keep the sand out, and then used a dremel stone to shape them to match the runner and gates of the oil bonded sand. I sprayed graphite on the mold to improve the surface finish of the casting.
All misruns today, but the chill wedge came out sweet. Grey all the way and there are three strokes with the file to test the softness.
Merry Christmas everyone. I wasn't ready for a CI pour yesterday, so I whipped up some simple foam patterns to make an indexing head for the EDM work on the castings. I set the head up in the "A" axis on the CNC and made 15* locating holes around the circumfrence. That is the angle between the head fins on the engine and will allow the use of the same electrode without re-positioning. I used some of my old oxide contaminated pieces to use them on something where appearance doesn't matter. I just melted and poured without even skimming. I came out decent. The "T" slot is metric on the EDM is metric, so I will have to use the vise on the bridgeport, or shim it on the EDM. And today I finished it. This is one of the lost wax cylinders for a mock up.
I ended up with some core blow in the Harley cylinders, but it was soft iron so I started machining to fit the rotary fixture. They were awkward to hold, so I heated them in the toaster oven and used them as a pattern to hot shape a foam sandwich. Then poured them in aluminum without coating since the finish is no concern. With just minimal cleanup and machining to create a step for repeatable orientation I bored out the cylinder and then switched to the CNC and a keyseat cutter to square the flange and cut the OD. I had thought I would need to use the cutter to machine below the flange, but ended up cleaning that up on the lathe. Then I mounted it on the rotary fixture ready for the EDM tomorrow.
