Spru cutter not cutting clean

[Pahaska]

I'm using a new "Mountain Molds" double cavity, aluminum mold. I'm trying to cast .511", 535gr, Lyman #2 alloy. The sprue isn't cutting off cleanly and my bullet weights are varying from 530-536 grains. I've tried adjusting the tension on the sprue cutter without too much pressure, varying the hardening time after the pour, paying attention to temperature differences of the molten alloy (between 650-800). After the initial warm up, the bullets fill the cavities well. The dramatic weight varyances concern me. I'll be installing Gator long gas checks but without trimming the "cut off nipple" on the bullet base, the gas checks will want to and do, rock on the bullet base. Help please...

[swamp]

I would try smoothing and polishing the bottom of the sprue plate. Maybe do the hole sides also.
swamp

[swamp]

I would try smoothing and polishing the bottom of the sprue plate. Maybe do the hole sides also.
swamp

[Hick]

How cool are you letting the lead get before you cut the sprue? I have one mold that way and I make a point of cutting the sprue when the lead is still close to melting. Of course, doing this tends to smear some lead on the mold-- but if you time it right it gives a very smooth bottom on the boolit without excessive smearing.

[Pahaska]

Hick, I let the puddle get all frosted before I hit the sprue plate. After I just watched a you tube video, the guy was cutting the sprues off of a 6 cavity mold and not even a bit of apparent resistance. With "my" two cavity mold, I need to wrap the sprue extension pretty hard (in my opinion) with my wood block. I'll try cutting the sprue off faster. Thanks for the help.

[Bazoo]

I get buns on the base if i let the sprue harden too much before cutting. I also trim those nubs with a razor knife when cool, but try to avoid them all together.

[Winger Ed.]

Try cutting the sprue the instant the puddle turns to the dull/frosty color.

[HWooldridge]

I set my plates to be pretty loose because it’s easier to hold them flat with upwards pressure on the pour spot. Very much spring tension can cause a plate to occasionally lift away from the blocks.

[daengmei]

the guy was cutting the sprues off of a 6 cavity mold and not even a bit of apparent resistance

If he was using a 6 cavity was it the same diameter bullet? Smaller would cut easier. You're waiting too long as others have said.

[samari46]

Try wearing some welder's gloves and when you cut the spru use some downward pressure. If that doesn't work, take the spru plate off and use some 320 grit silicon carbide paper on a hard flat surface to flatten it. And if that doesn't work, you most likely have to recut the spru hole in the spru plate. I use the center drills I use in my lathe. Just enough to leave a sharp edge. Drill press works fine. Then use the silicon carbide paper to get rid of any burrs caused by the drilling on the underside of the spru plate. Frank

[bedbugbilly]

Just my thoughts . . . if it is supposed to drop at 535 grains and you are getting 530 to 536 . . . that indicates to me that you are getting some air voids within the bullet causing it to drop at 530 or so. It happens. Just because a mold is "rated" at 535 grains does not mean it will drop at 535 - can't speak for your mold but Lyman molds are very prone to being "off weight". I have been casting close to 60 years and have cast a variety of heavy hollow base and plain base bullets. I ladle pour. I have some molds that have always given me a variance in weight Most times, I pay little attention to it - but that's me.

On some of the molds that that . . . I have found that by keeping the mold hot and by increasing the temperature of the lead they work better. I also pour over my pot with the ladle raised above the sprue and allow the lead to continue to pour instead of just pouring until there is a small puddle on top of the sprue plate - i.e. pressure pour to insure complete fill of the mold cavity.

On your .511 mold, the sprue hole is certainly smaller than the diameter of the base and you say you are getting what aniybts ti a raised dunole grin the sprue cut. That would indicate to me, as others have suggested, that perhaps the bottom of the sprue plate should be carefully polished (I have had to do it on some molds and I use a wide fine oil stone and gently rub the bottom of the sprue plate back and forth a few times to insure that the bottom of the plate is completely flat with no small burrs from machining the sprue hole). I would also check the top of the mold blocks when the two halves are together with a straight edge to insure that they are flat and not "off" from the machining. I would also check the bottom of the counter sunk sprue hole - the edger of the hole at the bottom of the sprue plater - to take sure that it was properly achieved and a sharp edge that will give a clean cut to the sprue.

Getting and maintaining a good pouring cadence is also important. Everybody has they won way - personally, I have never used a hot plate to heat a mold up. I set it on the pot while the lead is melting, when ready to cast, I pour two or three and dump them back into the pot until the mold starts dropping good ones and move on to cast. . . . but that's me - more than one way to skin a cat.

It sounds like you are getting good fill and a sharp, full gas check base to seat the checks - but just have the problem with the raised nub in the center of the base. Again . to me . . that indicates a sprue plate that for some reason is not shearing the sprue off cleanly. After you check the sprue plat and the top of the blocks . . . I think I would try experimenting with my lead a little hotter and see if you can't get a cadence going that would give you a good sprue cut. Cut too early and you[ll get a smear . . . to late and you may have an issue like you are having . . .. only trying different things will tell you.

On one and two cavity Ideal/Lyman molds - I have always worn welders gloves and used y hand to operate the sprue cutter - on both small and large diameter bullets. That said, I have two double cavity speciality molds made by a small supplier - both .375 flat based conicals - same size as Ideal/Lyman blocks but both . . . for some reason . . . . require me to use a wood mallet to cut the sprue . . . so go figure. IIRC . . . . although they are really well made molds . . . it took me some experimenting with lead temperature and casting cadence until I was able to get a good clean base on them.

If you can't get it worked out . . . then I would contact the maker and see what they suggest. I have some molds that cut better with the sprue plate being a little "looser" and others that seem to work better with it being adjusted a bit tighter. and some work better lubed and some don't. On my aluminum block molds . . . I tend to lube them more than any of my steel/iron block molds . . . but again, that's just me.

Good luck and hope you can get it figured out.

[gwpercle]

Make sure the sprue plate holes , the countersink areas , are deep enough to form an almost knife edge . If the "cutting edge" of the sprue is too thick it is hard to cut the hardened lead .
I had one like that ... the countersink wasn't deep enough and left too much dull edge on the holes , when I tried to cut the sprue they would leave a lump .
I got a counter sink of the proper angle (from hardware store) and chucked it in drill press and when I deepened the countersink it in effect gave the sprue cutting edge a sharper profile .
I looked at several moulds I had and matched the profile on them ... the profile is not a knife edge but a small vertical before the sprue countersink angle begins . For some reason the angle doesn't go all the way down to form a knife edge ... but nearly so .

Also tighten up your sprue plate and as you cast the heat will cause it to loosen so tighten it up as needed .
Make sure the sprue plate is dead level and clean ... smears and build ups will hold sprue open and cause the "Nubs" to form on base .
Don't forget to hold your mouth right ...that's important!
Gary

[45DUDE]

Hold the mold up to a light. Plate straight? Holes in the plate too large? Does the plate screw have a heat treated lock washer? Some plates are thicker than others. Once the thicker plate gets hot it works better. I ordered some extra 4 cavity plates for my Lyman molds and they are thinner than factory. If the mold is hot and the plate is hot and the plate is flat it should work.

[PopcornSutton]

Make sure the sprue plate holes , the countersink areas , are deep enough to form an almost knife edge . If the "cutting edge" of the sprue is too thick it is hard to cut the hardened lead .
I had one like that ... the countersink wasn't deep enough and left too much dull edge on the holes , when I tried to cut the sprue they would leave a lump .
I got a counter sink of the proper angle (from hardware store) and chucked it in drill press and when I deepened the countersink it in effect gave the sprue cutting edge a sharper profile .
I looked at several moulds I had and matched the profile on them ... the profile is not a knife edge but a small vertical before the sprue countersink angle begins . For some reason the angle doesn't go all the way down to form a knife edge ... but nearly so .

Also tighten up your sprue plate and as you cast the heat will cause it to loosen so tighten it up as needed .
Make sure the sprue plate is dead level and clean ... smears and build ups will hold sprue open and cause the "Nubs" to form on base .
Don't forget to hold your mouth right ...that's important!
Gary

This I found on one of the top mold makers. I looked at the sprue plate with a magnifying glass, and I saw a vertical end of the counter bore. Nothing cleanly cutting. I used a countersink tool and ran it in a little at a time until that vertical section was gone. Then I carefully smoothed the bottom if the plate so no burrs were there. Sliced the puddle off smooth as silk. You NEED a flat bottom!