New guy with mold making questions.

[B Mann]

I am completely new to casting boolits. I guess this falls into the right forum. I want to make 40mm Zinc pushers. They are kind of rare to buy and expensive. The molds seem to be none existent. I have some time and want to see what I can do.

I am thinking of machining out a mold to cast them. The Zinc pushers are approximately 1-5/8" in diameter with a hollow point on the bottom and the top. My theory is to make them sit sideways in the 2 halves of the mold. I am thinking to make the molds out of steel, because of the higher melting point of Zinc. Does this sound reasonable? Do you think they will cast well horizontal?

When you cast a boolit, after everything is cooled, can you drop a boolit in the mold and does it fit perfect? I am wondering if the mold is slightly oversize? In other words is the mold made to exact specs? or oversize?

This is what the pushers look like if you are not familiar.
322745

[Dave W.]

Molds are made a few thousands oversize, as the molten metal cools is shrinks some, this allows it to fallout of the mold. The castings are then pushed through a size die to get them the correct size. Good luck on your venture.

[country gent]

I would recommend steel for the material Zinc temps will be hard on brass and aluminum. For ease machining you want the dia parallel to the faces of the block flats top and bottom.
with the cups on each end its going to be a tricky mould to make. This because you need to core pins to pour the completed part. If you leave one of the cups out and pour from that end a small late and fixture you could cut the cup in after.

Pouring it 90* will leave a flat on the radius. You want a bigger spru hole for zinc so it may not fit on the band.

A set of blocks that big with core pin is going to be heavy to handle and may be to big for standard mould handles.

Cast Iron would be ideal here. Or steel next.

Square the 2 blocks up then drill for pins leave long. mill handle slots
set up in 4 jaw in lathe and bore cavity and bore for the core pin. Face top of blocks lightly while in the lathe, this ensures cavity is square with top.
back in mill drill the spru plate pivot hole and then the core pin locks pin holes. drill the handle screw holes.

The cup point and base are whatr makes this tricky cutting the base cup in a lathe or fixture in a drill press will make the mould much easier.

[B Mann]

Molds are made a few thousands oversize, as the molten metal cools is shrinks some, this allows it to fallout of the mold. The castings are then pushed through a size die to get them the correct size. Good luck on your venture.

No size die for me... But it will be a venture. Thank you.

[country gent]

Do to the different rates of shrinkage between zinc and steel the casting may or may not fit back in the mould. For zinc I think I would make the spru plate at least 5/16" thick to allow a big spru to draw from as it cools. Moulds are built with these shrinkage factors in the dimensions. Maqchine so you know it will be slightly undersized then lap mould to final dimension.

[HWooldridge]

I googled and they seem to be available as surplus for $3 to $5 each. Not sure how many you want but that seems cheap once the moldmaking and zinc costs are considered. They are very likely molded in a die casting machine in production volumes.

[B Mann]

I would recommend steel for the material Zinc temps will be hard on brass and aluminum. For ease machining you want the dia parallel to the faces of the block flats top and bottom.
with the cups on each end its going to be a tricky mould to make. This because you need to core pins to pour the completed part. If you leave one of the cups out and pour from that end a small late and fixture you could cut the cup in after.

Pouring it 90* will leave a flat on the radius. You want a bigger spru hole for zinc so it may not fit on the band.

A set of blocks that big with core pin is going to be heavy to handle and may be to big for standard mould handles.

Cast Iron would be ideal here. Or steel next.

Square the 2 blocks up then drill for pins leave long. mill handle slots
set up in 4 jaw in lathe and bore cavity and bore for the core pin. Face top of blocks lightly while in the lathe, this ensures cavity is square with top.
back in mill drill the spru plate pivot hole and then the core pin locks pin holes. drill the handle screw holes.

The cup point and base are whatr makes this tricky cutting the base cup in a lathe or fixture in a drill press will make the mould much easier.

That sounds like the idea I had. Thanks for the tips.

If I make the hollow points in both blocks (top and bottom), as part of the mold, Do you think I would have trouble releasing the piece?

I hate to do a lot of machining on each casted piece. These should be kind of true to fly well, but they do not have to be as precise as a bullet.

[country gent]

If you make both cores top and bottom then where do you pour thru and still be able to cut the spru flush. Side pour but then you have a stem to remove

[country gent]

The other issue I see is with that dia thin walls and short length fill out may be a problem with zinc temps. It will be a slow casting process with the time to cool and pour that much lead. And you may need a pause for the blocks to cool between pours. That much zink a 1000*-1100* may over heat the blocks.
cores top and bottom you wont open the blocks. the cores have to be removed to open the blocks or floating cores used. even with the floating cores the part wont release as the cores will be below the surfaces.

[B Mann]

I googled and they seem to be available as surplus for $3 to $5 each. Not sure how many you want but that seems cheap once the moldmaking and zinc costs are considered. They are very likely molded in a die casting machine in production volumes.

Pretty much what I have found, Except a little more expensive. So far I have not found any in stock right now and they tend to go fast when they are. I did pick up some used ones. 10-15 years ago they seemed quite plentiful, and cheaper. I am always a day short. (2 guys on Gbroker right now, one wants $9.50 each and the other wants $16.50 each, but they are new. 100 would be nice to keep me busy for a while.

I have access to some machines so I am looking for projects. I was thinking if this turns out well, I would try to make them out of Lead also. Lead is heavier and I would have to make them lighter. Lead would be much cheaper. They are reusable IF they are found. I am not sure how Lead would work.

With Zinc I could make them for about $2.50 each. With Lead about 40 cents. Plus time of course.

I am still pondering. One of those I wonder if????

[B Mann]

The other issue I see is with that dia thin walls and short length fill out may be a problem with zinc temps. It will be a slow casting process with the time to cool and pour that much lead. And you may need a pause for the blocks to cool between pours. That much zink a 1000*-1100* may over heat the blocks.
cores top and bottom you wont open the blocks. the cores have to be removed to open the blocks or floating cores used. even with the floating cores the part wont release as the cores will be below the surfaces.

Zinc melts about 150 F higher than lead. So I was thinking it was not excessively higher. A side pour with a spru removal would be acceptable to me.

The core part for the hollow ends seems to be the biggest hurdle to me. I could taper them slightly to help out.

[country gent]

B Mann you have a PM