Help w/Silicone Casting Problem

[jimrussell1]

I've recently purchased a Hilts Perfect Replica Mold which uses a set of silicone inserts and an aluminum mold you place your sample in before vulcanizing. It seems to work great with the exception of when I start pouring the lead. In a nutshell, my jigheads are coming out with a little "dent" in the head of the lead that I cannot get to fill in. I know that the problem stems from gas being trapped inside the mold, therefore causing the "dent", but I haven't been able to solve it.

The closest I've come to a perfect pour is with this combination: 1)cold mold, 2) low lead temp, 3)hot hooks and fiber guard inserts. I've experimented with every possible lead temp, different pouring angles, "venting" the cavities trying to let the gas escape, etc. Nothing seems to resolve this problem.

I read somewhere on here about possibly lightly dusting the cavity with talc to help lead flow, but I'm not sure that was referring the gas problem. I plan to try that tomorrow.

Does anyone have any experience with this problem and how to avoid it or fix it?

Thanks in advance for your help.

[siebler_custom_baits]

Very possible that your lead is too hard. Might wanna try adding some pure lead to the pot and soften a little. I too need to do this. I usually have problems around the collars on baits. Also try smoking mold with candel.

[jimrussell1]

Thanks CJ. Actually, I was using tire weights in the beginning, then changed to the purest lead I could find, old plumbing and some lead shot. The better lead helped but didn't rid me of the problem. I haven't tried smoking the mold yet. I'll probably try that this weekend too.

I appreciate it.

[Richoc]

You really should not smoke/candle carbon a silicone mold.

And talcing will not help with this.(can really mess you up if done wrong)

You need to make your gates larger.

And vent the cavity directly where the short is happening.

That way the air will direct vent, to the open air out side the mold.

Not to where it is still trapped, even buy the pour.

My bet is lead shrink.

Is there a big shrink hole in your pot when it cools?

You could just be having way to much shrink.

Only get the lead hot enuff to make the cavity fill.

Test pour till it is right be for putting any hooks, or fibers.

It will not handle much too heat like a alum. mold will.

Are you using a bottom pour?

[siebler_custom_baits]

oops forgot it was silicone mold. Yea i wouldnt smoke that.

[jimrussell1]

Thanks for the reply Richoc. Yes, my pot is a bottom pour model. It's one of the Lee pots. I've tried pouring at the lowest setting where the lead will still stay melted. That's the best results I have gotten, but I still have the "dent" at least on one side of the head. I have poured the cavity without the hook and insert and it seems to fill just fine if I remember correctly. I don't seem to remember seeing a shrink hole in the lead after it has cooled but I'll double check.

I have tried playing with the gate size and it really hasn't alleviated the denting problem. It's just made the gate bigger on the head unfortunately. I've tinkered around a little with venting the cavity, but I'm not really sure I've done it right. What is the proper way to vent the cavity? I've taken a razor blade and made a slice into the head of the cavity and ran that slice into a channel in the mold outside of the head, but I don't think I had the channel running out to open air.

Venting has been a problem for me though. I haven't been sure how big to make the vent into the cavity, how to make it for sure, etc. I'm guessing that to make the vent big enough for the gas to escape I'll have to make it so that there will be a little sprue to cut off from the vent. Does that sound right?

Any advice you have for properly venting the cavity would be surely appreciated. Thanks Richoc.

[Richoc]

You can really get larger than you think with the vent.

If you cut a "z" or zig-zag in it the lead will not flow past that point.

The change of direction with stop the flow of the lead.

Carve it out as a tiny "v"grove just on one side.

And it must make it to the out side of the mold, to release the air.

Down, up or to the side makes no diff.

A razor slice will not do it.

Pressure when you clamp the mold shut can pinch that shut do problem.

Worst thing that can happen is you will get a little sliver to trim off.

But you will get a full part.

If you getting a full pour, without the inserts, more venting will help.

Still think your dealing with lead shrink.

Pure shrinks a lot.

Is this a small peice of lead compared to the inserts?

Lead cools quickly around the inserts, messing up the fill.

Make shure your pot is full, pressure is better that way.

Make shure to over fill the gate when you pour.

Make shure the gate surfaces are as smooth as you can cut them.

Any little edges will hinder your flow.

Do you get a shrink dimple in the top of the gate?

Can you post a picture off the mold.

Made I can get a look at the set up and be of more help.

If you do not want it public e-mail it to me.

[Pop]

Hi Jim,

Other than the problem you are currently having with the mold. What is your opinion or the mold? Do you need a vulcanizer. The web site really doesn't explain how to make a jig mold with the "Replica Mold". Any instructions you can give would be appreciated. Thanks, Pop

[jimrussell1]

Hey guys. Well it's been a couple of days since I've had a chance to get back out and try the ideas. Well, this evening I went out to start some work and wouldn't you know it, my lead pot is dead.

But I've got two good ideas to try. The venting is one. Also, I got to talk to another tackle maker that has run into the same problem and the way he gets around it is, immediately after the pour he tilts the mold and taps it on the table. It has to happen pretty fast. He says this causes the gas to move out and allows the lead to fill in. So I'm excited to give these options a try but I gotta go buy a new lead pot tomorrow.

Richoc, I did find out that my lead is shrinking a little. It's not too bad though. There is a little bit of a dip in the top of the pot when the lead cools. I appreciate the info on the venting. I'm sure anxious to get to work on it.

About the inserts, and hooks for that matter. I have been heating the hooks and the inserts on top of the pot while I'm pouring. I think this helps keep the lead from cooling too fast.

The other things you mentioned about the lead cooling, having a smooth gate, keeping the pot full, etc, are also things I've found that helps. I've had a lot of trial and error. I'll try to get you a pic when I get some time.

Hey Pop, the Hilts Perfect Replica Mold does work very well. I don't think at all that the problems I'm having are related to the mold, as much as inexperience working with silicone. If you're looking to replicate a bait or modify one and make a mold out of it, the Hilts PRM is the best option I've found. I've tried Durham's water putty several times and it is much more difficult to work with. You'll probably want to purchase a couple of extra sets of silicone inserts to get the hang of it. And if you're wanting to pour very quickly you'll want an extra mold. The mold has to cool down for a minute or so before it will pour good again. A dremel tool with some small engraving bits will come in real handy too. Depending on your hook size, you may have to grind away some of the mold itself so the hook will fit.

If you have any questions at all feel free to give me a shout. jimrussell1@yahoo.com I've got the mold making down pretty well I just need to get past this pouring problem. I'm just about there.

I'll try to post an update tomorrow after I get the new lead pot.

Thanks guys.

[Richoc]

Was holding this trick back, so no one though I was crazy.

But you have heard it already.

Do not wait, till after the pour.

Jiggle the mold while the lead is pouring.

Like a drunk having the DDT shakes.

Small shaking, vibrations.

It is how a few of my costum molds have to be worked.

Most have cleared up buy anding in vents.

I add vents to all my do-it molds that will not pour well.

It really helps get the shorts down to zero on some of them.