eelslinger Posted February 14, 2014 Report Share Posted February 14, 2014 been lurking for a long time and obtaining loads of info from u guys. Finally started carving some prototypes out of wood and making two part RTV molds out of them from casting resin. But, the RTV is really expensive and I cant afford to keep using it for prototypes. Bondo is less expensive, so I was wondering if a casting resin such as feather-lite, smooth cast 300 or other similar resins would release from a 2 part Bondo mold or would the resin fuse to the Bondo? Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted February 15, 2014 Report Share Posted February 15, 2014 You can certainly keep the parts from fusing, with a release agent. Lots of options for this, do a TU search on 'release agent'. The issue is you will be using a hard master with a hard mold. The problem will be removing your master from the mold without damaging it, as you will want to use it more than once. Obviously the same goes for the casts too. Depending on the size, curvatures and angles, you may be fine, or you may have to introduce a pin to push the cast out, which will give you a little cleaning up sanding to do, or you may lose your master or damage the mold at the first attempt. Yes, it is cheap and worth a try. Maybe make a quick, rough master for testing the idea, before committing to your true master. The master needs to be as smooth as possible, a coat of epoxy always works well. Another issue is shrinkage, resin shrinks a fair bit, especially if you don't use any fillers. The shrinkage on a 2-part mold will be in your favor, away from the master, but you will end up with a larger cast than the master. You can reduce the shrinkage some, by mixing say a 50/50 of resin and automotive filler. They are both resin based, but check that they both smell the same. You can use either hardener, but I use the liquid hardener, as it is easier to mix. In conclusion - definitely possible, as long as you are aware of the problems and address them effectively. It may take you a couple of trial practice runs to get it to work, but well worth the effort. If you crack the method, you may not want to bother with the RTV. If you do have a go, it is important that you report back. We all want to know how you got on, success OR failure, especially after me doing all this typing Dave Quote Link to comment Share on other sites More sharing options...
eelslinger Posted February 15, 2014 Author Report Share Posted February 15, 2014 Thank you Vodkaman, I will report back in a few days, hopefully with successful results ! Quote Link to comment Share on other sites More sharing options...
eelslinger Posted February 19, 2014 Author Report Share Posted February 19, 2014 So, the 2 part Bondo mold parted fine with lots of Vaseline. BUT, turns out u cant pour casting resins with it. The resin is to thin and seeps threw the seem of the mold. The Bondo's rigidity does not allow it to seal properly. Plastisol and lead should be ok, but not thin resin. I was prepared for this to happen so I poured it with the mold sitting in an aluminum pan. Saved me from having a huge mess !!!! Quote Link to comment Share on other sites More sharing options...
eelslinger Posted February 19, 2014 Author Report Share Posted February 19, 2014 Time to bite the bullet and use rtv Quote Link to comment Share on other sites More sharing options...
mark poulson Posted February 19, 2014 Report Share Posted February 19, 2014 Maybe you can save the mold by cleaning the faces and then coating them with thin bondo and resqueezing them to get a better fit. You can sqeeze them until most of the new bondo is out, and then, once it's set, clean out the cavities again. I'd try something like that before I'd junk the mold. Quote Link to comment Share on other sites More sharing options...
eelslinger Posted February 19, 2014 Author Report Share Posted February 19, 2014 Good idea, that reminds me of something else, maybe a little easier. I was thinking of brushing on that rtv head gasket maker. It flexes just enough when squeezed. Ill let you guys know if it works Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted February 20, 2014 Report Share Posted February 20, 2014 Pure resin is too heavy as a lure material anyway, with a specific gravity (SG) of 1.2. Water has an SG of 1.0 so resin is heavier than water and will sink fast. When I used resin, I added as much micro balloons as I could, using a cake icing hypo to inject the thick mix. This should solve your leakage problem. Dave 1 Quote Link to comment Share on other sites More sharing options...
eelslinger Posted February 20, 2014 Author Report Share Posted February 20, 2014 I hear ya vodkaman, but the lure I'm trying to make is not meant to float, its actually going to be anywhere from 1 to 4 oz sinking for fishing in saltwater surf or inlets where heavy weights are needed to get down in current. I might try a floating version eventually using featherlite . Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted February 21, 2014 Report Share Posted February 21, 2014 I hear ya vodkaman, but the lure I'm trying to make is not meant to float, its actually going to be anywhere from 1 to 4 oz sinking for fishing in saltwater surf or inlets where heavy weights are needed to get down in current. I might try a floating version eventually using featherlite . I getcha. Perhaps mix some resin filler, just purely to thicken up the mix. The resin filler is normal weight, so should still give you your design requirements and stop the leak. DAve Quote Link to comment Share on other sites More sharing options...
