one-off baits Posted October 2, 2015 Report Share Posted October 2, 2015 Hey guys. So I made two silicone molds of the same bait and same master, one after the other. The first is made of lure craft silicone and the second is MF silicone. The problems I'm having is on the first mold is all of the baits are coming out with a bunch of roughly1/8th inch (and smaller) dents all over the bait. I know it's not bubbles in my plastic and I'm pouring everything the exact same in both molds and the baits are coming out much different. Anyone have any idea what going on here? It's killing me Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 2, 2015 Author Report Share Posted October 2, 2015 They're 6" swimbaits with a decently deep belly. The dents are circular and range in size. It's weird it's in one mold and not the other with every other factor the same. I'm going to try to get some crappy phone pics when I get off work in the morning Quote Link to comment Share on other sites More sharing options...
JRammit Posted October 2, 2015 Report Share Posted October 2, 2015 First thing that comes to mind is temperature A picture will help alot Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 2, 2015 Author Report Share Posted October 2, 2015 Temperature of the plastic? I've tried it hotter than normal and on the cooler side. The problem mold has thicker walls and has more silicone mass than mold #2 but when pouring everything is the same and mold #2 comes out great. All of the dents are circular by the way. Looks a lot like bursted bubbles but smoother. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 2, 2015 Report Share Posted October 2, 2015 Are you injecting or gravity pouring? How is the mold clamped together? Is the Lurecraft a much harder material than the MF? Have you tried pouring the MF first and then the LC? Are you using a thermometer, if so, what temp are you pouring? Dave Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 2, 2015 Author Report Share Posted October 2, 2015 (edited) Open pour silicone molds that I made. The .LC mold is softer. I didn't bother recording the temps. The hotter pours were around 330-ish and the other pours were between that and about the viscosity of the coolest youd want to pour. And yeah I've varied the order poured as well. Edited October 2, 2015 by one-off baits Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 2, 2015 Author Report Share Posted October 2, 2015 Oh and btw, the softer one (.LC SILICONE) is the trouble mold Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 2, 2015 Report Share Posted October 2, 2015 As I understand it, dents are caused by the plastic shrinking. as the plastic shrinks, more plastic is drawn down from the pour hole reservoir, so you must make sure that this is topped up. If you were injecting, then you could simply keep the pressure on a bit longer. The first part of the cavity to solidify is the pour neck. Once this happens, no more plastic can be drawn down and so dents are formed. To be honest, I was expecting the harder RTV to be the problem, so you see, I too am learning here. One thing that has never been suggested before, is to tighten the clamp say a quarter turn, say about 10 - 15 seconds after the pour. This slight increase in pressure might be enough to counter the shrinkage. Just something to try. Report back if it works or not. Another idea, is to have a shaped stick/dowel to lightly press down on the sprue, to keep pressure on the plastic. The problem of dents comes up often, so with a TU search, you should come up with more ideas and suggestions. I am not an experienced pourer, but this problem intrigues me. Dave Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 2, 2015 Author Report Share Posted October 2, 2015 (edited) There are no clamps, sprues, necks, or any other things like that. It's a simple home made silicone open pour mold. I've been pouring a long time and I know all about the "typical" dent problems with injection molds and how to solve them. This is something crazy. Pics are coming in the morning.... Edited October 2, 2015 by one-off baits Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 2, 2015 Report Share Posted October 2, 2015 Ah, I see now. All that is left, is some contaminant on the cavity surface. A thorough clean with acetone or alcohol is all that is left, but I am sure that you have already thought of this. Dave Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 2, 2015 Author Report Share Posted October 2, 2015 I tried soap. I'm going to try cleaning it with alcohol and if it doesn't work I'm want to try something and make another mold......can I use regular fiberglass resin and pour it into my good mold to make another hard master or will it mess up my silicone &/or shrink too much?. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 2, 2015 Report Share Posted October 2, 2015 Yes you can, but there will be shrinkage. Try it and compare with the master. If the shrinkage is too much, you can mix the resin liquid with Bondo, which is made of the same resin (smells the same). Tou can use either hardener, I usually use the liquid hardener that comes with the resin, as it is easier to control in small amounts (drop count). It will still have shrinkage, but not as bad. Dave Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 2, 2015 Author Report Share Posted October 2, 2015 As far as measuring out hardener, use the recommended amount based on total volume of resin + bondo or just the amount of resin used Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 2, 2015 Report Share Posted October 2, 2015 Just add the hardener that you would if the entire volume was resin. DAve Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 2, 2015 Author Report Share Posted October 2, 2015 What kind if bondo to mix with the resin? Bondo gold filler, bondo body filler, bondo resin jelly, or bondo glass? Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 2, 2015 Report Share Posted October 2, 2015 (edited) The equivalent that I use (cannot find Bondo here in Indonesia) is the stuff used for car body repairs. Just to be safe, mix a little and test it on the back of the mold, but I am 95% sure that it will be no problem. Dave Edited October 2, 2015 by Vodkaman Quote Link to comment Share on other sites More sharing options...
Little Creeper Baits Posted October 2, 2015 Report Share Posted October 2, 2015 Hey one-off not sure what type of silicone you are using, or what your model is made of but platinum cured silicone can be problematic with certain materials. Curing on platinum silicone can be inhibited by a wide range of material. Having said that I still think it Is the best for making molds. I buy from Reynolds Advanced Materials. They carry Smooth on products. I have tried almost all of them. I like the Sorta Clear 18 for most molds and masters. Quote Link to comment Share on other sites More sharing options...
Little Creeper Baits Posted October 2, 2015 Report Share Posted October 2, 2015 Temperature of the plastic? I've tried it hotter than normal and on the cooler side. The problem mold has thicker walls and has more silicone mass than mold #2 but when pouring everything is the same and mold #2 comes out great. All of the dents are circular by the way. Looks a lot like bursted bubbles but smoother. Just re read your post. It sounds like there are air bubbles in the silicone just outside of the surface of the mold. This creates an artifact like are describing because the hot plastic pulls the air toward the surface and leaves a dent. You need to make sure to burn in a silicone mold. Run a few pours through it this will toughen the surface and also take away the dull finish. All of our molds are burned in for at least two pours, and we reuse the plastic. Vacuuming the silicone helps a lot but you still need a little burn in time with silicone. I hope this helps. Benno 1 Quote Link to comment Share on other sites More sharing options...
Frank Posted October 2, 2015 Report Share Posted October 2, 2015 Well said Little Crepper. Bubbles in the silicone are expanding when it is hot and causing this. I know this sounds expensive but a vacumn chamber will get all the bubbles out but you have to work fast and make sure you master does not have any bubbles either. Don't make any molds like that any more but did back in the day. Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 3, 2015 Author Report Share Posted October 3, 2015 Air bubbles just inside the surface of my mold? Sounds possible. Here is a pic of two baits poured at same time. Left is my MF silicone mold, right is my LC one that giving me problems. Both came from same master Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 3, 2015 Author Report Share Posted October 3, 2015 (edited) Looking at multiple baits, the bubble pattern isn't consisted with each other so idk if it's bubbles under the surface of mold? So what is a mold burn Edited October 3, 2015 by one-off baits Quote Link to comment Share on other sites More sharing options...
Little Creeper Baits Posted October 3, 2015 Report Share Posted October 3, 2015 Air bubbles just inside the surface of my mold? Sounds possible. Here is a pic of two baits poured at same time. Left is my MF silicone mold, right is my LC one that giving me problems. Both came from same master I can't see your pics, but there is an unbelievable amount of air in silicone. If you degass it will almost double in volume during the process. Even in our vacuumed silicone molds we still get a very faint artifact like you describe in the the first pour or sometimes the second that is caused by air in the mix. I sent you PM call me if you to talk about this. I am on west time but I'm up pretty late. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 3, 2015 Report Share Posted October 3, 2015 I learned a bit more today, as I do most days here on TU. Dave Quote Link to comment Share on other sites More sharing options...
djs Posted October 3, 2015 Report Share Posted October 3, 2015 Not sure if this might be the problem but I have seen people here complain about the same thing with LC molds they sell. Don't know if the silicone molds they sell is the same material as the silicone they sell for making molds. Might be some kind of additive in the silicone. I have made many molds from tin and platinum cure silicone without degassing and never had that problem. I have used M&F, smooth on mold star, and Raw Materials brand silicones. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 3, 2015 Report Share Posted October 3, 2015 Standard advise from manufacturer, is to brush a coat over the masters before pouring, to ensure a bubble free layer. Then pour away from the masters in a fine stream, this helps release any bubbles and as the mix flows over the mold, the bubbles rise. I am of course assuming the masters are bottom mounted and not floated. Dave Quote Link to comment Share on other sites More sharing options...
