Vertical Mold Fill - Is it a Venting Problem?

[Taterhead]

Greetings.

New caster here. I have a problem, and I think that I know the solution, but wanted to check my logic before wrenching on things.

Background:

I am casting from a Pro Melt. The mold is a 2 cav Lee .401 175 Gr TC. Alloy is 3% antimony and about 1% tin. Lead is 720-750 degrees. Pretty sure the mold is up to temp since I had a pretty long, steady casting session. Generous sprue puddles each time (played with smaller puddles too, no change). Pouring from about 3/8" above the mold. I cleaned the mold vigorously, and finished carefully with Qtips and rubbing alcohol very meticulously. Smoked the cavities a little.

The issue:

The bullets are not completely filling to the top of the sprue plate. I think it is a venting problem. Iget really good fill-out laterally, but not top-to-bottom. The edges and lube grooves are sharp and crisp. Full diameter. But the sprue cuts leave a pronounced little stump, usually - except when the technique is modified as below.

What leads me to believe it is a venting problem is that if I slow the flow rate to a thin stream, and focus on letting the stream of lead go directly into the center of the sprue hole (leaving space for air to escape out of the sprue hole), then I get good top-to-bottom fill. The problem is that the flow rate is too slow (or maybe not enough pressure) and I don't get good lateral fill. On the cavity closest to the sprue plate pivot, it has a tendency to not fill if the pour is not perfectly centered. Leaves a little nub of a bullet. Almost seems like an air bubble keeps lead from filling. Again, a nice puddle on the sprue plate. If I get a good centered pour, good lateral fill out. But if I get a good lateral fill out, typically the base it not filled to the top.

I wonder if the sprue plate it too tight? One thing I did notice is that the sprue plate is badly gouging the top of the mold, and it drags pretty good. A bit of a rough finish, it seems. It has nicked one of the sharp edges of the BB contour. No biggie, probably. I been using one of those mold lube pens from NOE.

Is it as simple as unscrewing the sprue plate screw a little? I have a NOE 5 cav 180 gr mold on the way, so I don't mind messing this Lee up a bit. I'd like to learn how to not mess up a mold first before using the NOE. Not too much $ invested. Thought I'd check with the awesome veterans here to see if I'm on the right track.

Thanks guys.

[country gent]

It may be a venting issue. You may be able to slightly loosen the screw to take the drag away and allow better venting. The bigger surface area under the plate doesnt help venting alot either. You might try a fine stone. of 600 grit wet dry sand paper backed by something flat. Use this to very lightly bevel the top edges of the mould blocks at the top you want to see just a small flat at 45* on each block. This makes a vent line right at the tops of the blocks under the sprue plate. I would also lightly stone the sprue plate flat to remove dings and burrs, along with the tops of the blocks.

[runfiverun]

I'm pretty sure you still have a heat problem.
not enough in the sprue plate area.
that nub is from cutting the sprue after the boolit has cooled off just a titch too much for a 2 cavity aluminum mold.
you almost want to see a tear in the boolits base.
speed up the count and your pour rate try for about 4 pours a minute.
this should be like 4 seconds to fill a 3 count to open and 7 seconds emptying the mold and replacing it back under the spout.
the extra second is for when the mold is up to temp and you then count to 4 before cutting the sprue.
as you get the mold hot you count longer and eventually you'll be at about 3-3.5 pours a minute.

[Mk42gunner]

One good thing about two cavity Lee molds, if you screw them up you aren't out much money.

Your problem does sound like a too tight sprue plate, along with a burr on its underside. I would try to gently loosen the pivot bolt, it won't take much. I have also deburred the under side with a stone.

Sometimes cleaning the smoke residue from the vent lines is enough to let the air out.

Good luck,

Robert

[Taterhead]

I'm pretty sure you still have a heat problem.
not enough in the sprue plate area.
that nub is from cutting the sprue after the boolit has cooled off just a titch too much for a 2 cavity aluminum mold.
you almost want to see a tear in the boolits base.
speed up the count and your pour rate try for about 4 pours a minute.
this should be like 4 seconds to fill a 3 count to open and 7 seconds emptying the mold and replacing it back under the spout.
the extra second is for when the mold is up to temp and you then count to 4 before cutting the sprue.
as you get the mold hot you count longer and eventually you'll be at about 3-3.5 pours a minute.

Hey thanks. That timing cadence is useful to keep in mind!

I thought a lot about the heat thing (having learned much from you and others on here, thank you). Over a session of casting 300+ bullets, I played with pace. Going fast; getting the sprue plate really hot where it takes 8-10 seconds to frost over. Then slowing down and running a bit cooler. Same result. As you said, cutting the sprue a bit earlier did pull that little plug too, bases were a bit flatter, but still a bit of a vertical void beneath the sprue plate. Then turning the flow rate WAY down to a trickle such that the lead was not engorging the sprue hole (allowing space for air to escape out the top), filled to the top. But, as I said earlier, poor vertical fill out.


So not disagreeing with good advice. I might not have given all of the pertinent info.

Thanks!

[Echo]

My meager response is to increase the Sn %. I always want between 2 and 3% - anything over 3 is wasteful, less than 2 gives fill-out problems.

[runfiverun]

venting can play a roll in fill out in the mold.
but if the plate is too tight it usually only affects one of the cavity's [the one closest to the bolt]
one thing to keep in mind is that the new 2 cav. lee molds use left handed threads on the sprue bolt.

if the plate looks flat on the mold and swings pretty easily I would just break the top edge of the mold right along the cavity edges with a sharpening stone.
just 1-2 passes on each side at a 45* angle.

[44man]

I don't see a venting issue pouring from a height, air can get around the stream.
More temp related I would say. A good suggestion to loosen the plate and also to cut the inside corners. But if there are no burrs at the cutting hole, DO NOT polish the bottom of the plate or mold top.
One thing you should do is to file and polish the plate edges so they don't scratch the mold top and I bet that is what is scratching.
I hope you have a thermometer for the Pro Melt. Friend has 3 and none get hot enough and cycle so slow that lead is always changing. My Lyman got so bad lead froze in the pot.
Cutting too soon can get a lead smear on the plate too and that WILL gouge the aluminum.
I ladle pour only myself, hate bottom pour. Get a ladle and make boolits!

[Taterhead]

I do have a thermometer, and no issues with temps so far. Melt temps are pretty close to indicated temp on the thermometer.

[popper]

file the inside top of the mould. get the sprue plate hot. the plate cools the alloy at the top too fast and it won't flow for proper fill out. try dipping the plate in the pot to heat it.

[44man]

I do have a thermometer, and no issues with temps so far. Melt temps are pretty close to indicated temp on the thermometer.
That is good but mold temp is more important. A cool mold will freeze 900° lead before it fills.
Venting takes very little, I cut vents on one block only and leave just end mill marks on the top of the mold and bottom of the plates.
The more time it takes for the sprue to set, the better the boolit. Time is where it is. A few seconds is too short for a set sprue. To hurry for another few boolits to toss is just loss. Take your time. I prefer 100% perfect and no rejects. Fill the mold soon but don't hurry to cut.
My ladle method is to put it tight to the mold, turn up and HOLD long enough for the boolit to take molten lead from the ladle, NOT THE SPRUE! Then let it harden enough to cut.
Some call it pressure filling but how much from a ladle? No, it is what the boolit needs.
Lead from the bottom is cooler from the start, no elements at the bottom, then slag. Then you cool in the air to reach the mold. Lead is freezing when it touches a cool mold.
The plate has a lot of surface area like a heat sink. Pour a bench top of lead to keep the plate hot, c'mon, I make a small sprue with no spill. I don't want a leak at the ladle.

[mdi]

Just a thought; are you allowing for a large "puddle" on the sprue?

[Taterhead]

44Man, my remark about a thermometer was a direct response to your direct question about whether I have a thermometer, and whether I had the same temp issues with my Pro Melt that your buddy allegedly has had with 3 of his. Nothing more.

Even though I am new, the concept of a hot mold and sprue plate are well understood from a theoretical standpoint. The hands-on experience is a work-in-process. Through the process of elimination, I deduced that I did not have a sprue plate that was too cool. Otherwise 730 degree lead would not loiter for up to 10 seconds before frosting. No change to the vertical fill. Lateral fill was spot on.

I'm going to work on the venting issue this weekend. Thanks everyone for the great tips about how to think about that.

[Taterhead]

Just a thought; are you allowing for a large "puddle" on the sprue?

I would say so. I played with larger (mostly larger) and smaller over the course of casting over 300.

[rintinglen]

Good advice so far, I can only add two things.
One other thing to be aware of, or at least to consider. 3/8" is a little bit high in my estimate for your pour. I would suggest you narrow that gap down to 1/4 inch and run your melt a bit hotter. Hot lead, a full pot, a large sprue and a hot mould should get you good fill out.
Another thing to check is the rate of flow. Adjustment of the screw that limits the lift of the handle can allow the flow to increase, try a half turn and see if that helps.

[yondering]

Even though I am new, the concept of a hot mold and sprue plate are well understood from a theoretical standpoint. The hands-on experience is a work-in-process. Through the process of elimination, I deduced that I did not have a sprue plate that was too cool. Otherwise 730 degree lead would not loiter for up to 10 seconds before frosting. No change to the vertical fill. Lateral fill was spot on.

I'm going to work on the venting issue this weekend. Thanks everyone for the great tips about how to think about that.

In my experience, poor base fillout is almost always related to venting, especially if it does it when the sprue puddle takes 10 seconds to harden. First thing to try is just loosen that sprue plate, easy to do and you'll know right away if it helps.

You can also stone a light bevel on the top edge of the blocks where they join, forming a little vent groove that runs across both cavities. You can get away with a little tighter sprue plate with this vent added.

It sounds like you're doing the right things with temp and alloy, so venting is the next thing to look at.

One last thing - I would not slow down the pour; if anything, make it faster.

[44man]

44Man, my remark about a thermometer was a direct response to your direct question about whether I have a thermometer, and whether I had the same temp issues with my Pro Melt that your buddy allegedly has had with 3 of his. Nothing more.

Even though I am new, the concept of a hot mold and sprue plate are well understood from a theoretical standpoint. The hands-on experience is a work-in-process. Through the process of elimination, I deduced that I did not have a sprue plate that was too cool. Otherwise 730 degree lead would not loiter for up to 10 seconds before frosting. No change to the vertical fill. Lateral fill was spot on.

I'm going to work on the venting issue this weekend. Thanks everyone for the great tips about how to think about that.
I understand and venting could be the problem but everyone gives good advise. It is trial and error in this game.
I have been casting something from lead for 73 years, sinkers, jigs and then boolits. I was about 12 when I made my own jig mold, 4 banger with cut outs to hold hooks. I was a fishing nut. Kitchen stove stuff.
I thought I knew it all until I started making my own boolit molds to find learning never stops.
I don't criticize, just offer experience. I am 79 and in all these years I have never made a bottom pour work as good as a ladle, I admit to being a DUD with it. I hate to toss a single boolit. Yes I get one now and then but it is my fault. I can fix before another bad boolit.

[popper]

IIRC that is a bevel base so there is no venting in the BB area. Alloy flows through the sprue hole and flows outward to the base edge but air has no place to go and expands rapidly - so poor base fillout. File a slight 45deg. across the top of both blocks. Next probable problem will be 'nicks' on the base but not at the block separation. I made my Lee a FB vs BB to solve the problem.

[Yodogsandman]

venting can play a roll in fill out in the mold.
but if the plate is too tight it usually only affects one of the cavity's [the one closest to the bolt]
one thing to keep in mind is that the new 2 cav. lee molds use left handed threads on the sprue bolt.

if the plate looks flat on the mold and swings pretty easily I would just break the top edge of the mold right along the cavity edges with a sharpening stone.
just 1-2 passes on each side at a 45* angle.

Do this^^^^. Just one or two swipes with a sharpening stone right where the two mold halves come together on top. I like to break the edge on the sprue plate outside edge, too. It prevents a lot of the drag marks across the top of the mold.

Most of the time I can cast an inch from the spout and don't care much how the stream goes in the sprue hole. Open up the spout so that the lead alloy comes out just fast enough to not cause a rooster tail that's trying to come back up out of the cavity. Adjust the stream as the pot gets lower, with the less volume of lead, it will have less pressure.

Cast fast enough to keep the mold and sprue plate hot. Leave a good sized puddle on top of the sprue plate for the cavity to draw on as the cavity cools. As the alloy cools in the cavity, it sucks more alloy from the puddle. Cast fast and don't even look at the first 50 or so. They go back in the pot. This just gets the mold heated up. Don't inspect boolits till you're done. It slows down your cadence and allows the mold to cool down. When you notice that the boolits are coming out frosted or with a greyish, velvety look, you can slow down a little.

The larger or taller the boolit, the faster the stream needs to be, with more volume flow to fill the cavity right.

Good luck with your new hobby!

[runfiverun]

the long skinny boolits do like a straight quick shot right into the cavity.

[44man]

I have never depended on the sprue to feed a boolit or sinker. It hardens faster then the boolit and quits. When you see a divot on the sprue as it cools, you already lost fill.
The plate must be hotter then melting temps to feed.
My sprues do not have a divot on them. Only shrinkage of the sprue itself. Most are FLAT.

[popper]

I've heard many times that you get better boolits when it's humid. So, started looking at the steam tables. Dry air @ 70F gets to 180psi @ 400F, closed container. Moist air doubles that. pressure increase with 200F air isn't as great. Compare that with the fractional psi of a 1/4"dia. x 1/2" long stream of lead (~50gr.). High air pressure wins over light weight of Pb every time. Good venting for the entire cast is required!

[fredj338]

venting can play a roll in fill out in the mold.
but if the plate is too tight it usually only affects one of the cavity's [the one closest to the bolt]
one thing to keep in mind is that the new 2 cav. lee molds use left handed threads on the sprue bolt.

if the plate looks flat on the mold and swings pretty easily I would just break the top edge of the mold right along the cavity edges with a sharpening stone.
just 1-2 passes on each side at a 45* angle.

^^THIS^^ In finicky molds, where the bases won't sharpen up, even with pour spout touching the molds, breaking the edge of the mold halves has helped.

[Taterhead]

A new NOE 180 RF 10mm mold arrived yesterday, so I'm a little less motivated to work on this Lee mold. Man. What a difference in quality! That being said, I do intend to workout this mold for the sake of educating myself.

I'm going to start with slightly loosening the sprue plate. I'll get it hot and keep it hot. If that doesn't work, I'll try the venting mods described.

Thanks for the great feedback guys. I'll let you know how it goes this weekend (although it is snowing and might get distracted with some skiing if the mountain is open).

[Taterhead]

Well, loosening the sprue plate a touch helped immensely. It only took about 1/8 to 1/4 turn to make a difference.

Thank you runfiverun for letting me know about the reverse threading!

The mold does seem to have some venting issues. A bit stubborn. Almost seemed like in was pouring lead on top of a bubble if I didn't get the pour perfectly centered in the middle of the hole. It did make a pilr of nice bullets though.

Casting immediately after with the same alloy, same temp, with a new RCBS 150 SWC was a totally different experience. That mold seemed to suck lead into the cavities. Very telling. That RCBS mold was nice to work with.

EDITED TO ADD:

I might try the venting thing too. That might wait since I'm anxious to try my new NOE mold in a similar profile.

[44man]

Venting is very important of course and breaking the inner edges really does wonders. It takes very little, just a deburr actually.
I tend to keep my plates tighter then factory molds. I surface the mold blocks and plates with an end mill, the swirls left reduce friction and aid venting. They also keep lube in the swirls better.
The worst are dead smooth and polished plates. I tried lapping to make poor fits, no way to keep them flat and had to mill in the end. The most I do is a swipe or two to deburr the cutting hole. It gives me perfectly flat bases with no bumps. I will chunk a little out now and then but it has no affect on a boolit. Just heat related.
I use Lee, Lyman, RCBS and Saeco molds exactly the same. My lead is just set at 750° on the Lee dial and all else is timing. Molds are pre heated to 500° in a little oven. If everything is at full heat my first boolit is perfect and can empty 20# without a reject. Pure goes to 800° for the lead.
With all the experiments with molds since I started to make mine, I have learned a lot but still can't make BP work. I can make some good ones but the problems with that spout are not worth the time. I want 100 boolits for a gun I want 100, not throw half back in the pot. I cast for so many guns and have so many molds, I don't want to fool with them.
Only mold I had trouble with was a borrowed huge brass custom, work of art but it needed more heat and broke my wrists after a while. I got it to work but to get that frantic when I am the slowest caster here does not fit. It reminds me of when I used 3, 2 cavity molds at once.
Casting is as boring as trimming 2000 cases. I need dancing girls on my bench to keep me awake!
I prefer problem solving and once they are gone, it is drudgery in the extreme. I really hate to cast and load ammo. I hate to clean guns.