one-off baits Posted March 9, 2016 Report Share Posted March 9, 2016 So I've been making molds like crazy this past year. Have a little over 70 styles made into resin molds and a few into silicone. I hated the bubble problem with silicone and stayed away from it. Now its time....I have a vacuum chamber kit on the way and I'm scared to death of it. One of my big questions is can I put my molds into the chamber after I pour the silicone in? Will the vacuum pull my glued down baits up off of my pans any? Besides that...any help, hints, tips, & safety into that comes to mind, please share with me. Thanks, matt. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted March 9, 2016 Report Share Posted March 9, 2016 I have never owned a vacuum chamber, but would dearly love one. I keep my eyes open every time I go into town, but no luck yet. So no experience, but I can talk about the engineering side of things. Gravity still works inside the active vacuum chamber. It is not like outer space with everything floating around weightless. This means that your patterns will stay put, as will the silicone that you pour over them. Before you switch on the vacuum pump, the air bubbles in the silicone are at room/atmospheric pressure, which is at around 14Lb/sq inch. When you switch the pump on, the pressure in the chamber drops to close to zero. The air in the bubbles now expands, pushing outwards with that 14Lbs/sq inch until the pressure in the bubble is equal to the pressure in the chamber, close to zero. This causes the bubble to greatly expand, and as we know large bubbles have more upward force, to fight their way through the thick siicone fluid. When the vacuum is released and the pressure returns, what few bubbles didn't make it out of the silicone, are compressed by the atmospheric pressure and pretty much disappear. Safety wise, just follow the instructions that come with the chamber. Keep it on a flat level surface, so there is no chance of dropping, floor is good for this purpose. Don't try making your own chamber unless you REALLY know what you are doing and understand the forces at play. There is a reason why the word implosion sounds like explosion. You are really going to enjoy this tool. No need to fear it, just respect it. Dave Quote Link to comment Share on other sites More sharing options...
one-off baits Posted March 9, 2016 Author Report Share Posted March 9, 2016 Thanks man. About the glued down bait theory...there will be bubbles beneath the lure when I pour the silicone and vacuum it. Think they will expand enough to cause issues? Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted March 9, 2016 Report Share Posted March 9, 2016 That is a good point, and this is were those with experience could jump in and help you. Another point of engineering theory is the rule of least resistance. Water, air, electricity, all flow along the path of least resistance. You have to make it so that the master is attached to the base firmly enough that the least resistance is around the master and/or make sure there is no air underneath. My preferred method of mounting masters is to sink them into soft modelling clay, like plasticine. After rolling out the clay, you could vacuum the clay to get rid of any air bubbles. But if you prep the clay well, this may not be necessary, but I just don't know. I really hope someone with experience jumps in here and teaches us both. Dave Quote Link to comment Share on other sites More sharing options...
Basseducer Posted March 9, 2016 Report Share Posted March 9, 2016 The most common use of a chamber is to vacuum the silicone before you pour it over the master in the mold box. Quote Link to comment Share on other sites More sharing options...
SlowFISH Posted March 9, 2016 Report Share Posted March 9, 2016 The most common use of a chamber is to vacuum the silicone before you pour it over the master in the mold box. +1.... I helped a friend make some bike grips with a silicone mold. Found out gassing it before - pour the silicone without adding bubbles (no real trick other than don't dump it) and then out gassing it again after pouring helped a ton. Not sure what you are making your masters with - but if they are wood/plastic and have a nice, clean flat side - you can try some 3M double stick.... not the crap you'd find at CVS...try the 3M 465 Adhesive Transfer Tape.... I actually use it to mount down PVC/Wood/REN to my CNC table and it holds while I cut parts out if it's something I can't clamp. This should allow you to apply it, trim, then mount down in your box... might be worth a try. J. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted March 9, 2016 Report Share Posted March 9, 2016 Of course, silly me. De-gas and then pour, makes a lot more sense. Dave Quote Link to comment Share on other sites More sharing options...
mark poulson Posted March 9, 2016 Report Share Posted March 9, 2016 Pouring from a distance above you mold with a small, steady stream will cut down on bubbles, too. Quote Link to comment Share on other sites More sharing options...
majic man Posted March 9, 2016 Report Share Posted March 9, 2016 Largest problem with silicone is you gas the heck out of it mixing. Best value Vacs, awesome chambers for a great price. Quote Link to comment Share on other sites More sharing options...
one-off baits Posted March 9, 2016 Author Report Share Posted March 9, 2016 Thanks for the tips guys. A lot of my masters will be soft plastics without a clean flat side. Yeah that's what I've been doing(using the 30lb double sided tape with a few drops of super glue gel for reinforcement lol. I guess I'll try degassing pre-pour and see if that'll do. Quote Link to comment Share on other sites More sharing options...
