FishBones Posted October 22, 2011 Report Share Posted October 22, 2011 I'm having somewhat of an issue dealing with the cooling shrinkage on my top pour swimbaits. You know, getting that concave back and that little hole at the top of the tail. Pancho suggested I pour twice, one run (sort of like doing a two color pour) then another a little bit later to top it off. I tried this with mixed results. If I topped off while everything was still molten enough it didn't seem to affect it much, as in it's the same as filling the mold all at once. If I wait a moment to top it off, I get lines on the side of the bait (like an air bubble trapped all around it), I can accomplish this without getting delamination (yay?) but the line is unaccecptable. Any help? Since switching to Bondo molds (from OOMOO)I seem to be having more of the issue, not sure why. Quote Link to comment Share on other sites More sharing options...
mark poulson Posted October 24, 2011 Report Share Posted October 24, 2011 Normally, top pour molds need a reservoir on top, like a big, deep sprue pouring hole, to allow for hot plastic shrinkage as it cools. I couldn't figure out how to add a reservoir easily on my swimbait molds, so I just pour them slowly, and keep the plastic temps down around 340+-, to try and reduce shrinkage. If I "overpour" and leave a big mound of extra plastic on top, sometimes it shrinks back down to the right height, but I have a lot of trimming to do. Mostly, I just live with concave backs. The fish don't seem to mind. Quote Link to comment Share on other sites More sharing options...
gone2long Posted October 24, 2011 Report Share Posted October 24, 2011 Yeah its a fine line between under pouring and over pouring I actually pour to above the top of the mold but not flowing out of it, it's a learning curve for sure and what your getting with the laminate issue is a cold crack so your leaving the first pour setup to long and prolly not pouring hot enough for the second pour to bond correctly, again it's one of those fine lines keep at it you'll find what works for you. Quote Link to comment Share on other sites More sharing options...
Smallie Posted October 25, 2011 Report Share Posted October 25, 2011 I pour over the top as well. If you find the plastic is running out of the mold and creating flash, try lowering the temperature. I pour around 310. Quote Link to comment Share on other sites More sharing options...
Uma62 Posted October 31, 2011 Report Share Posted October 31, 2011 I let them cool to just being tacky and then run a torch lightly over the top.It will smooth out the top and cover up any imperfections. Quote Link to comment Share on other sites More sharing options...
FishBones Posted November 7, 2011 Author Report Share Posted November 7, 2011 Thanks for the advice guys, uma, the torch idea was a "doh" moment lol, hadnt thought of that. Quote Link to comment Share on other sites More sharing options...
Uma62 Posted November 8, 2011 Report Share Posted November 8, 2011 I have been pouring a little extra to over fill the mold sort of trying to crown it.When the plastic cools down alittle so it wont stick to finger I put one of my aluminum molds on top and put alittle weight on it.They come out nice and smooth on top.Might have to hit it with tourch to fix a blemish here and there.But that is how I am tackling that cooling concave problem. Quote Link to comment Share on other sites More sharing options...
