Hard to cut sprue

[Slick Pilot]

I have a Lee double mold in 429-214 which is very difficult to cut the sprue.

I pour the lead at a fairly high temperature; about nine on a Lee Production Pot. I hold the mold about 3/4 inch from the spout and allow a generous puddle to form on the top, without running over the side. I then wait until the lead just frosts over, then cut the sprue.

That's where it gets difficult. I have to hit the sprue plate with force that I consider excessive to get the thing to swing. (With the mold empty, the sprue plate moves easily, but is not loose.)

I have other Lee molds, singles, that open easily when casting, using the same technique.

Any suggestions?

Thanks.

[Cherokee]

A hard alloy can be hard to cut. Also, check out the spru holes. The edge may not sharp. I have recut the hole so the cutting edge is sharp.

[David R]

Cast faster (get the mold warmer)

David

[44man]

I have seen a lot of factory sprue plates that were blunt. The edges of the holes should be very sharp to cut instead of trying to break the lead.

[Slick Pilot]

Okay, then how does one sharpen that sprue hole most effectively?

[Bret4207]

Slick Pilot- (either you're a whirley bird driver or a guy wearing a lot of gold chains and after shave), The best and easiest method I've some up with for sharpening sprue plates is to get ahold of a cone shaped Dremel grinding bit at Wal Mart. DO NOT CHUCK IT UP IN A DREMEL TOOL. Use either a variable speed drill or a hand cranked drill and just run the grinding bit/stone/whatever the right name is for a few seconds in the sprue hole of the sprue plate. You just want to "shine it up" a little. Then take the sprue plate and rub it on a good flat oil stone, like you sharpen a knife or chisel with, in a circular motion. All you're doing is getting rid of the burr left by the stone and flattening the sprue plate a bit. If you have a mold you can't easily remove the sprue plate from then just take the grinding stone and run it in the hole with your fingers or VERY lightly with the drill. Then take the oil stone and lightly run it across the bottom of the sprue plate 1 or 2 times. Run the sprue plate over a piece of wood and you shold be able to see if there are any burrs hanging down because the wood will catch on the burrs. Hit the sprue plate again untill the burr is relieved. You want the sprue plate as flat and sharp as you can get it. Go slow and easy. The last thing you want is some burrs hanging down from the sprue plate. They WILL gouge the moulds top surface and scar it up leading to all sorts of problems, especially on an aluminum mould.

[44man]

It is best to work from the inside of the hole. You can make a bob with abrasive on it to spin with a drill. Make the end the same shape as the taper the hole is cut at. A hard piece of wood would work, or brass, even lead. Smear with a fine abrasive and turn it slow until you raise a tiny burr on the bottom of the plate. Gently stone off the burr or rub it on 400 grit wet or dry sandpaper on a piece of glass.
You can buy small sandpaper bobs that are wrapped to a point or you can wrap fine sandpaper on a little stick by angling the wrap to form a point. Slit the stick or a metal rod and stick the end of the paper in the slot. Wind it on and tape the top end of the sanpaper to hold it. You don't want a stick or rod over 1/8" in diameter.
There are also fine, tapered grinding stones for Dremel tools that will work. You should re-shape the stone to fit the taper.
A lot of guys like to lap the bottom until the edges are sharp. But there is no way to lap the bottom and keep it flat. I have tried 1000 times to do that and I always wind up putting the plate on the mill to get it back to flat. The leading edges will always cut more then the center.
It doesn't take a whole lot to fix and should only take a few minutes.