Trying a Matchplate Pattern

[Jammer]

I've been wanting to make some spheres of a couple different sizes and have found some things I think will work. They are Tupperware tubs for keeping onion halves fresh, , I had to look them up to see what they were but I got them at a yardsale for a couple bucks. One is 4 3/8" dia and the other is 3 1/2" dia. I think Cast Iron will be 11.2# and 5.75#. I want them for a Muller and my son wants some for practicing shotput. The shotput needs to be 12# so I may have to use some of the build up paint that has been talked about in other threads. I only need about another 1/8". Or, I could cast it from Brass, that would be 13.5# so I could put a small core in it. Lead isn't good for kids or a muller so if I go that route I think I'll make a brass shell and pour lead into it.
Since these molds are only a hemisphere, I had to figure out how to line up the 2 halves. I made them from Plaster of Paris and put some pegs in, then, when I made the second half, I put the first half with the pegs on top while the POP set up. It seemed to have worked, I want them to dry some more before I paint them.

[Harry]

That is real close to the numbers SolidWorks reports for the weights Jammer. Nice find too for the pattern, how are you going to register them on a matchplate? I will generally drill a through hole while the parts are together then use a pin through the plate but with that being a shell I am thinking of how I would do it. Maybe fill them with something to be able to use the pin.

[Jammer]

I placed one of the POP halves on the matchplate and then rammed it up with greensand, flipped it over and put the whole thing in the drill press. I drilled 3 hole on the large one and 2 in the small one, plus an extra hole to use for extraction with a screw. It seemed to work pretty well. Casting one will tell the rest of the story. May test with some Aluminum or go straight to Cast Iron, depending on the mood I'm in.
I did some calculating and , if I cast a Brass shell with the large one and use the small one for the core pattern, I could fill it with Lead and have a ball that weighs about 16#. I'd have to cap the core ends with some pipe plugs.
Setting a sprue and riser has me baffled. I would like to use a horn gate to fill from the bottom but I can't think of an easy way to make one. May just go in the side with the sprue and have the riser come out the top. Do you think it will create too much turbulance? I'll have to keep shrinkage in mind too.

[Harry]

Guess I wasnt paying close enough attention, I was thinking you were going to use the hollow plastic sphere for the pattern. The sloid pop pattern should work out well.

These are pretty big pieces so shrink is really going to be an issue, for balls in a mill it wont matter but thats not the point I'm sure but at least you will still be able to use them even if less than perfect and it will give you a chance to experiment without having to scrap them for small defects.

The horn would probably be the best bet but if that doesnt work out I think I would try a tangential arrangement for the gate with a bit of a slope where it enters the sphere in the drag, not too much but just enough to let the metal slide down the side rather than be launched over the edge. The tangential entry I am thinking would set up a swirl rather than a wave that would move across then fold back onto itself churning if the entry is straight into the side. It also seems like it would help keep any debris in the center and push it up and out the riser.

Always interesting to see these things worked through.

[Jammer]

Well I've had a revelation. I don't need to make a match-plate, I have two halves of the sphere and can just ram one half and flip it, put the other half on and ram it up. DUH.

I didn't realize just how complex a horn gate is. You almost need to make one up for each different casting. It has to have a perfect curve so you can pull it out in a circular motion and a slight taper so it comes out easily. Maybe I can make one out of clay and bake it.
Where's Murray when you need him??

[Rocco]

Instead of a conventional horn gate, how about a horn shaped piece of styrofoam? Ram it into the drag with the pattern and leave in the sand to create sort of a hybrid mold which uses a conventional pattern for the actual part and lost foam for portions of the gating system.

[Jammer]

Something like that had crossed my mind. I just didn't know about doing a combo conventional casting with lost foam. I thought it might cause some gas issues or blow some of the sand out of the mold. I'm trying a small horn gate, waiting on it to dry, I'll see how that turns out.

[Harry]

Should work fine as a split pattern. I really like the ease of molding with a plate because you dont have to worry about pushing the pattern down by ramming when doing the second side.

For filling through the bottom you could use a cheek and place the two halves of the part in the top two (cope and cheek) and the gating/runners in the drag. Another option would be to pour with the parting line vertical then you could cut the sprue/runner/gate down and around the sphere. Just need to have an opening on one side of the flask and clamp a molding board on what would be the top and bottom of the mold if it were laying flat.

[Jammer]

Yea, I may have to use a cheek anyway. My flask is kind of thin and the ball is close to the bottom already.