BTL Posted March 31, 2021 Report Share Posted March 31, 2021 Hi guys, new here. Been reading like crazy for weeks and finally joined, what a wealth of information this forum is. Anyway, I'm tired of inconsistent hand poured baits so I'm planning to make a 4-cavity injection mold for a wire-thru soft plastic bait I've been working on. I don't have a picture on hand, but the bait is similar in size and shape to a Rapala Subwalk, just made of soft plastic. The line tie and hook hangers are in the same locations. This will be my first injection mold and I'm not sure where to locate the sprues and vents on this bait. My first thought was to put the sprue on the chin just below the line tie. Another idea was to just make the sprue straight out the tail, meaning I'd be injecting right over the rear hook hanger, and just trimming off the plastic after I'm done. I'd like to place it so it's both inconspicuous and also fills efficiently. Im also not sure if there's a strategically advantageous location for vent hole(s), or if a vent can go anywhere. I'd appreciate any suggestions for locating the sprue and vents! Quote Link to comment Share on other sites More sharing options...
SlowFISH Posted March 31, 2021 Report Share Posted March 31, 2021 All depends on a few variables.... How many cavities are you making / need? Are you planning on using a dual color injector at some point? etc... For example - if just one cavity and your baits are only going to be 1 color... honesty you can pretty much do whatever you want to some degree provided you vent the mold properly.... meaning you can inject from front or back - probably even the belly or top and vent the front/back. 1 bait provides alot of flexibilty... its when you try filling 2/4/6 at same time that sprue location gets trickier to place anywhere other than the "typical" spots after you stack baits up. If multiple cavities - you'll probably have to choose front or back.. and considering your placing a wire in there which will cool the plastic pretty quickly - I'd lean towards the front to avoid the bait "shutting off" too quick (due to cooling fast) and then you'll be fighting dents in the thicker part. Personally - if I was just making for myself, only worried about a single color and not worried about efficiency / time... I'll be temped to make a 1 cavity - inject in the belly or between belly/front hook hanger. If you plan to use a dual injector at some point - you'll need to try and get that injection point closer to "middle" so I'd inject right under the front hook hanger close to the nose so you can get a top/bottom color scheme going. I'd stay away from the rear hanger - I think you'll fight the wire cooling the plastic at that point too quick and your thick section/belly upfront will dent. I always try to (when possible) place the injection sprue as close to the widest part of the bait as you can get it... as its last part of bait to cool and as it does - it can still pull plastic from the injection runner. Hope that makes sense. J. Quote Link to comment Share on other sites More sharing options...
BTL Posted March 31, 2021 Author Report Share Posted March 31, 2021 Great reply, thanks. I was planning for a 4-cavity mold. The baits will be single color, I paint them afterwards. I didn't think about the wire cooling the plastic, that's interesting. Maybe that's part of why my hand poured baits have been inconsistent. Sounds like I should probably go for somewhere between the line tie and the belly hook hanger since that's the thickest point. Maybe a small vent on the back near the tail. Quote Link to comment Share on other sites More sharing options...
SlowFISH Posted March 31, 2021 Report Share Posted March 31, 2021 23 minutes ago, BTL said: Great reply, thanks. I was planning for a 4-cavity mold. The baits will be single color, I paint them afterwards. I didn't think about the wire cooling the plastic, that's interesting. Maybe that's part of why my hand poured baits have been inconsistent. Sounds like I should probably go for somewhere between the line tie and the belly hook hanger since that's the thickest point. Maybe a small vent on the back near the tail. That's probably the best place to start.... also remember - the bigger you make the injection runner (dia) the better... think about the baits cooling.... in a perfect scenario - the tail cools/solidifies first and it slowly cools moving towards the nose and then your injection runner cools/solidifies last. That "should" allow the bait to keep sucking in "liquid" plastic from the injection runner the whole time.... which eliminated the dents. I've made a bunch of molds where I tried to be "cheap" on how big (diameter) of an injection runner I made to "save" plastic.... usually I end up regretting it and go back and machine it larger in diameter. Now I try to make sure to always have the injection runner wider in diameter then the thickest part of the bait... if you look at most molds being sold - the ports are pretty much the same diameter the whole length - which is usually around .625"-.65" in diameter. J. Quote Link to comment Share on other sites More sharing options...
BTL Posted April 1, 2021 Author Report Share Posted April 1, 2021 I'm glad you mentioned the injection runner, that was another dimension I wasn't sure of. I think my bait is about .70 at it's widest point, so I guess I may want to widen out the runner below the port. Yeah it will eat up a lot of plastic, but it's worth it if the results are better. Quote Link to comment Share on other sites More sharing options...
SlowFISH Posted April 1, 2021 Report Share Posted April 1, 2021 + 1 on widening port near the bait - it's all about controlling the dents - last part to cool dents the worst. Luckily that wire will help a little as it will absorb some heat notably cooling the tail first. J. 1 Quote Link to comment Share on other sites More sharing options...
