Rate My Mold/ Help

[Cabrilla Grande]

I just finished my first mold, and it came out of the CNC machine beautifully....but the pouring results weren't as great as I expected. My concept is a football style jighead with a flat on it so I can glue on a molded eye.

Also let me say I am a machining student not an engineer or tool and die maker.

They all came out like this:

Horrible! I was pleased with the fact that there was no flashing on the parting line at all and that the hook fit perfectly but otherwise they look like crap.

So my question is... is it my mold or is my lead/ technique?

Here's what I used. Lee pro pot 4 10lb bottom pour on max heat setting.

I admit I am unsure of the lead purity... I just remelted about a few pounds of old egg sinkers I had on hand.

I didn't order any other lead yet and I really wanted to try it out!

I did flux it with candlewax and skim the junk off the top.

No release agent.

I did a few pours with no hook before to heat up the mold, also.

Here are pictures of my mold. (pictures are before I deburred it)

The questions I have regarding the mold are:

Do you think my gate is big enough? It's 1/8 inch diameter.

I noticed I only filled out the barbs and shank if I poured the stream directly into the gate. Is that normal?

I was hoping I could just fill up the sprue without having to be super accurate with my lead stream.

Should I make the sprue shallower so I can see the hole better?

Would more vent slots help?

Any constructive criticism on the mold would be great.

I do plan on ordering some quality lead soon I just wanted to know if I should revise the mold first before I try any more pours.

Also... how full should I keep my Lee Pot? Will it hurt it if it's only like 1/4 full?

Thanks!

[pirkfan]

I'm not crazy about the shape of your sprue hole, the bottom is almost flat where the hole goes through to the head. A lot of surface area for the aluminum to wick away heat and cool your lead. I'd machine the hole to approximately the shape and dimensions of the pouring spout on the lee pot so you can put the spout in the sprue hole when pouring. I'd also enlarge the 1/8 hole a little, that's a pretty small opening for lead to flow through freely.

[Vodkaman]

The venting looks good. Could possibly lose the mid shaft vent, but it is not causing any problems.

I appreciate what Pirkfan is saying about the gate hole, but I would be interested to find out what diameter other commercially available molds use as a gate hole diameter.

Their are things you can try before attacking the mold. Cooler lead, hotter mold, different lead. Consider a mold release spray. Read this post by Cadman: http://www.tackleunderground.com/community/topic/18965-lead-mold-release-spray/

Dave

[toadfrog]

P.S. That's a really nice looking mold. I struggle to get them looking that good.

Crank up the heat on your lead. Make sure its clean and has no dross floating around in it. Set it about 9 on a lee pot. lay the mold on top the lead pot as you heat it up. I see no reason why the mold should be the problem. Its a very good looking mold. If you want the flat for the eye to be recesses just drill the center of the flat and set a flat head rivet in it. You will be pleased with the result. Also put more of a funnel taper in the gate bottom. I think the concave shape is creating sort of a vortex not letting your lead gravity feed as it should.

Edited October 22, 2010 by toadfrog

[Cabrilla Grande]

I'm not crazy about the shape of your sprue hole, the bottom is almost flat where the hole goes through to the head. A lot of surface area for the aluminum to wick away heat and cool your lead. I'd machine the hole to approximately the shape and dimensions of the pouring spout on the lee pot so you can put the spout in the sprue hole when pouring. I'd also enlarge the 1/8 hole a little, that's a pretty small opening for lead to flow through freely.

I did the sprue that way to save time. It's slotted with a 1/2" ball nose endmill. To make a conical shape on a 3 axis mill I would have to do a surfacing toolpath which takes much longer. I saw that most of the soft plastics molds that bear/ del make have this style sprue so I thought I would try it out.

[Cabrilla Grande]

lay the mold on top the lead pot as you heat it up.

Oh cool, good idea. I didn't even think about that as a way to heat it up. The mold itself got pretty warm to where it was uncomfortable to hold it very long w/o gloves but it never got super hot. I guess I'll give it another try! Thanks.

[sdsaw]

Nice machine work!

Your mold looks good, but I think that you need to change the shape of the pour hole.

Not positive if you need to change the sprue hole

I made my first mold from scratch a short while back.

I made the pour hole exactly like yours and it gave me problems with the lead hardening in the pour hole area before the cavity would completely fill. I think that it was caused by the flat area at the bottom, disrupting the way the lead flowed

What ended up working much better was a cone shaped pour hole that I recut with a ground endmill. I'm certain that a counter sink would work just fine

With a pour hole of this shape, the lead can hit the sides and just keeps on flowing

Copying one of my other molds, the sprue hole is done with a ball endmill that was cut to depth of less than it's radius

You end up with an oval sprue hole that is easily trimmed flush with gate cutters

Mold release spray or candle soot will make a BIG difference on the quality of your pours

I'm able to use straight WW lead in the mold that I made

Hope I was clear in explaining this.

If not, just ask

Scott

Edited October 22, 2010 by sdsaw

[smalljaw]

Pirkfan and Sdsaw are spot on, I'm not a machinist but I know from years of pouring lead that the wrinkles you're getting are caused but uneven cooling of the lead and the fact that your pour is complete tells me that everything is hot enough so the reason for the uneven cooling is flow rate and the culprit is usually the sprue hole. I had several molds that did this and all it took was widening the hole a bit but keeping it cone shaped and it solved the problem.

[meallenjr]

I wish I could do that

[pirkfan]

I did the sprue that way to save time. It's slotted with a 1/2" ball nose endmill. To make a conical shape on a 3 axis mill I would have to do a surfacing toolpath which takes much longer. I saw that most of the soft plastics molds that bear/ del make have this style sprue so I thought I would try it out.

The sprue hole on Bear's molds is that shape to accomodate the tip of an injector. There can be some parallels here, if the sprue on your mold is shaped to accomodate the spout on a lee pot, and you hold your (heated) mold against the spout, the weight of the lead in the pot exerts a slight positive pressure on the lead pouring into your mold which helps a little in getting complete pours. This effect isn't huge because the stream coming out of the lee pot isn't very big. Another benefit, the lead stream will automatically be aligned with the sprue hole.

[dlaery]

When you say they look horrible, what do you mean?

I think you mold looks good and I agree with what was said about the spru. The spru needs to be not round but in the shape of a slot, I have attached a pic of one of mine. I draw a cone shape down to a narrow slot or oval where the spru goes into the cavity. I think the slot actually alows air to escape to fill better.

Edited October 22, 2010 by dlaery

[airbrushextreme]

try twisting the sprue off instead of cutting it also I have a couple of hand made molds also I used a precision sandblaster to smooth out the inside to keep it from skipping (not filling out) I also would try a little larger hole for the spout other than that I think it looks great

[Cabrilla Grande]

What ended up working much better was a cone shaped pour hole that I recut with a ground endmill. I'm certain that a counter sink would work just fine

I think the ball mill slot is already too deep to make into a cone without having to face off all of my top alignment pin holes in the corner. I kind of want to make a steeper angle than 90 anyway. I'll just to use that for my next mold. I like the idea of your oval shaped gate making it easier to cut off the sprue. Thanks, dude.

Another benefit, the lead stream will automatically be aligned with the sprue hole.

Yeah I can definitely see the benefit of that now.

When you say they look horrible, what do you mean?

I meant the finished pours looked horrible. Sorry.

try twisting the sprue off instead of cutting it

Thanks for the tip.. Ill give it a try. I just used some dykes. I haven't had a chance to buy some gate cutters yet. Precision sandblaster sounds interesting. I do have some buffing compound and a dremel... think that would help?

--------------------------

Oh, and thanks for all the advice everyone. I had a few other mold designs that were ready to cut but I decided to revise them so I just made a top pour plastic mold with my machine time today. They're shrimps.

[mkvnmtr]

I have never used a mold that was not hot enough to burn me if I did not have gloves on. And I mean burn me good. After about three pours it is going to be too hot to touch the metal. If you found that was not the case you probably need the mold hotter to make a smooth pour. I also use wheel weights for most jigs because I seldom paint and they stay bright longer. Even as small as 1/32 of an oz seems to pour fine. Just make sure there is no zinc in the mix.

[mark poulson]

Could you fill the sprue holes with JB Weld, and redrill them with a countersink?

You might even try RTV silcone, since it stands up to lead just fine.

[Cabrilla Grande]

Here's an update. I not only modified my original mold but I finished a second mold incorporating some of the tips you guys gave me.

The original still pours a little wrinkly but at least I can get it to consistently fill everything out now. The wrinkling only occurs on the flat face where I plan to put a stick on eye so I can deal with it.

It fills out so well now that the lead even goes into the vent holes...

I believe expanding the gate hole to 5/32 in. made a much bigger difference than making the sprue conical, though. Unfortunately making the hole bigger also made it way uglier where you cut the sprue off. I got flush cutters now but it still looks like I'm gonna have to sand or file it a bit and I'm not really looking forward to that at all since I don't want to have to deal with heavy metal dust.

Here's the second mold.

I used a surface toolpath to make the cone 60 degrees since I wanted a steep cone and the steepest cutter I have is only 90 degrees. I was hoping I could actually just stick the nozzle into the tapered cone and pour away but the sprue cools and sticks to the nozzle so I still have to hover over the nozzle and "aim" into the gate.

Definitely a few things that I would want to do over on the 2nd mold. I think I made the eye recess too deep... it's very hard to get it to pour. I also made 4 alignment pins and made it fit too good! If I had to do over I would only use 2 alignment pins on the mold centerline and give it a looser tolerance so I can pull it apart easier.

I have a few things to try still. Next mold definitely making the vents smaller since I don't want to deal with microflash. I'm also going to make the sprues shallower so I can see the gate better to aim into it.

Also going to bring the original molds back to the shop and remove a bunch of material from the back so that they heat up faster.

And I'm still waiting for my friend to give me the welding rod that I was gonna use as a weedguard pin!

[sdsaw]

I've found that the vent holes can be relatively shallow. (.010 deep and only needs to be on one side)

It looks like you have added vents for the main body on the bottom surface

I don't think that those are necessary

If a vent is needed for the main body, I would add it next to the pour hole so the air will vent up as the cavity fills.

You will find that after you apply the release spray, the lead will flow much better through the pour hole and not harden as quickly. So, definitely apply it to the pour hole also.

I agree with the need to shallow up the pour hole.

It will make it easier to see how the lead is filling the cavity

I feel that a 82 deg. or 90 deg c'sink would make a more proper pour hole.

Have you considered making hinged molds instead of separating molds?

Edited November 2, 2010 by sdsaw