Base fill out dificulties

[brewer12345]

I was casting today with a new-to-me 5 banger rifle boolit mold made by Noe that I got from a fellow member here. The three cavities closest to the handle cast nicely, although the middle cavity required an abnormally large sprue puddle to behave well. The two cavities furthest from the handles were hopeless. Everything I tried gave the same result, shrunken, rounded bases. This was an alloy with plenty of tin, so it wasn't the metal. I tried hotter, cooler, tightening the sprue plate, loosening it, big sprue puddles, etc. Nothing worked. Is this something to do with my technique, the mold, the handles, or some adjustment I failed to make? Once I gave up on the two problem cavities I banged out over 500 nice keepers which will last me a looonnngg time, so no worries. I just would love to know what was going wrong.

[tazman]

This may sound a little corny, but some cavities prefer the lead to go in the center of the hole and some like it to flow down the bevel and into the hole.
It varies from mold to mold and sometimes from cavity to cavity in the same mold.
Most of my molds don't care as long as the lead and the mold are both hot. I have one that will only fill out when run down the bevel.
I think it has something to do with how the lead swirls as it goes into the cavity.
I also have one that will get flashing between the sprue plate and the mold if I run the lead in through the center of the hole nearest the pivot pin.
This assumes you are using a bottom pour lead pot.

[country gent]

May be a slight venting issue with the mould. Another thing is on a new mould a few sessions may be needed to Break it in and develop the patina that's makes the old moulds cast so well. Maybe give it 2-3 more sessions before trying to fix. As stated above moulds are a thing unto themselves and every one likes certain things. Just like rifles.
I would recommend a hard cleaning of vent lines, a soft touch with a scribe awl or ice pick thru the vent lines just enough to remove any hard build ups. Check the sprue plate over good. Try again, If this dosnt work you might try lightly beveling the tops of the blocks with a sanding stick. just break the edge .005-.008 X 45* down each top edge where the blocks mate. This gives a vent line right under the sprue plate.

[Boolit_Head]

My 5 cavity aluminum molds from NOE like to run surprisingly hot and I've noticed the furthest seem cooler for some reason. I have however gotten good fill out of all cavities.

[Dusty Bannister]

Some like to cast starting at one end and letting the overflow fill those further down the block. Lost too much heat so those were cold. I like to start at the far end, have the mold end lower than the handle so over flow goes away from the empty cavity. Start, stop, move to the next hole, start, stop, etc. Limit the amount of drop as well to preserve heat in the stream. Do it quickly and it almost forms a bead like a weld and the sprue comes off in one piece.

[brewer12345]

I've cast over 10,000 boolits in more than a dozen molds in the last 6 months. It ain't fill technique, as far as I can tell. I've noticed that many-cavity aluminum molds really like to be run hot. The Lee 6 bangers in particular seem to want to be almost at the point of frosting to cast well and avoid wrinkles. I don't usually run those molds hot enough and so I end up with too many rejects for my liking.

I looked at the mold when I noticed the problem, but without reading glasses on I would easily miss something small. Will look really closely at the mold and see if I can tell what is going on and whether can rectify the problem.

[Yodogsandman]

I sometimes alternate which end of a gang mold I start filling it from, from starting at the front cavity, to starting at the rear cavity. always leaving a big sprue puddle.

[waco]

Preheat mold on hot plate. My guess is mold is too cold.

[Grmps]

make sure the vent swirls inside the mold are clean
make sure the sprue plate isn't too tight so air can escape between the sprue plate and the top of the mold (the sprue plate only has to be tight enough to get a smoot cut on the base. don't sinch it down, that can damage your mold)
make sure your lead flow isn't too slow
add a little more tin
if the above doesn't help get a fine diamond hone (or sharpening stone) and ease the inside corners of the mold VERY LIGHTLY along the cavities to allow better airflow DON'T TAKE TO MUCH OFF!! Compare the amount you take off to the size of the vent lines in the mold.

I run my 311-232-FN NOE at 690°

I like to start filling the mold at the end where the sprue pivots - that's where the most resistance will be.

[Rcmaveric]

I swear my molds all have a personality of their own and as well as the alloy sometimes makes them change a bit. I just tinker with and try different things. Like tapping the mold, adjust the tempeture of the melt, run the mold hot, pressure fill the cavities, fill one cavity and keep the stream flowing while filling the next cavity, or alternating cavities. I have tried adding tin sometimes helps, but sometimes doesn't. LOL maybe if i would use known alloys and not my mix mash BHN of Lord knows what i wouldn't have problems. I make it work though and sometimes takes some tinkering. Once you figure out what the mold and alloy wants it goes quick.

[Hickory]

I was casting today with a new-to-me 5 banger rifle boolit mold made by Noe that I got from a fellow member here. The three cavities closest to the handle cast nicely, although the middle cavity required an abnormally large sprue puddle to behave well. The two cavities furthest from the handles were hopeless. Everything I tried gave the same result, shrunken, rounded bases. This was an alloy with plenty of tin, so it wasn't the metal. I tried hotter, cooler, tightening the sprue plate, loosening it, big sprue puddles, etc. Nothing worked. Is this something to do with my technique, the mold, the handles, or some adjustment I failed to make? Once I gave up on the two problem cavities I banged out over 500 nice keepers which will last me a looonnngg time, so no worries. I just would love to know what was going wrong.

You have what I call a mould with personality.
And I only cast the cavities that give me what I want.

[243winxb]

Venting problem. I am sure you tried "Pressure Casting"

[brewer12345]

I did preheat the mold. Almost seems like a must with aluminum.

Anyone have a picture handy that shows the vent lines in a mold? Don't really know what I am looking for.

[243winxb]

Compare vent lines on your problem mold. The cavities that cast ok, compared to the ones that don't.

Have you tried pressure casting. Bottom pour spout in full contact with the mold?

[brewer12345]

243, I take it the vent lines in your pic are the horizontal lines leading away from the cavities? What should I be looking for in the way of problems? Stuff plugged up in the lines?

Have not tried pressure casting before. Perhaps that is the answer.

[Minerat]

The vent lines are those groves across the faces. They have to be clean or open to let air out as alloy goes in. I use a popsicle stick sharpened to clean the lines, it also helps if the mould is hot. I try to avoid using metal but have found that if you get a very fine dental tool like used to clean teeth you can gently open up blocked lines. My dentist lets me have their old ones for free, ya just have to ask.

[brewer12345]

Thanks, minerat. Will get the mold out and look very closely at it.

[popper]

'Break' the top edge of the mould - file, knife edge, whatever. Cast hotter alloy. I noticed this morning, pouring PB in a 2x that the first sprue cooled faster than the 2nd and had barely perceptible rounding of the base. I also pour and let the mould drop onto a hard surface before the sprue can solidify to help base edge. Also found that dental floss at the sprue pivot helps clean out 'junk' there. Mould just warm enough to open easily and floss the pivot bolt under the plate. Did 1/2 pot this morning without needing to re-lube. I sent my Lee 6x RD down the road years ago - too hard to keep the plate hot. Start pouring at the pivot bolt end.

[kens]

sounds like a minor bit of oil or contaminate in those 2 cavities

[winelover]

Most casting issues, are because the mould isn't hot enough. I can tell mine are up to temperature.....when I can easily cut the sprue with a gloved hand.

Winelover