jkustel

Making Bait Lighter....

29 posts in this topic

Hey guys,

I am relatively new to molds and resin casting baits. I got some wood masters made and the cast molded baits have come out good which is encouraging. I have one particular design that requires exceptional buoyancy to be optimal...somewhere around basswood or very light poplar. I can get moderately close using roughly 50% resin to 50% MB's....I've found that at least with the resin I'm using that I can't really exceed this ratio and still have a consistency that I can pour into the mold. Even at this ratio I need less weight and more buoyancy to hit the numbers I'm looking for. The cast bait using this formula comes to about 2.3 oz. (its a 7" lure) raw blank without hardware. My best wood models (same dimensions) perform best at about 1.75 oz. Based on this I need to lighten my cast resin bait at least .5 oz. to achieve similar performance in the water. I am going to attempt to achieve this weight reduction by placing ground foam pellets (from packing peanuts) into the mix to displace more volume and bring the weight where I need it. My hope is that the urethane won't break down the foam chemically and defeat the purpose. I am considering adding some fiberglass mesh to make up for the loss in strength if necessary....

Please advise if you have any thoughts or better method for bringing the weight down more than microballoons alone will allow for....

John

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I used a cake icing syringe to inject thicker mixes if MB's. The best I could get was a specifig gravity of around 0.65 with the consistency of thick mustard. This is still way heavier than basswood.

The foam pellets might work, but forget about the fibreglass, they are heavier than water and their use would be counter productive. Some members have been experimenting with cork as a filler. Here is a link to a recent discussion: http://www.tackleunderground.com/community/topic/21891-sealing-plastics-crankbaits/page__p__163082__hl__%2Bcork+%2Bballoons__fromsearch__1#entry163082

You might be better changing to a different casting material, such as 16Lb foam. It is very strong and at 16Lb/cuft (SG=0.25), it is lighter than basswood and just a bit heavier than balsa. It is a two part expanding foam.

Dave

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Would airplane balsa work. You could though wire the wood in order for it to sit in the middle then pour. Or depeding on the bait make a hard outside then cut in half and fill with foam a la Dahlberg.

Has anyone tried to coat a wood bait with plastic instead of epoxy. That was I could use this really light balsa for something?

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I am staying poised with the molds but I see why some guys go back to wood.....I tried introducing chopped foam into the mold and then poured the resin...what a mess. It created all kinds of voids in the bait-junk. Time to get some 16lb. foam before I throw in the towel. With lightweight poplar and substantial ballast weight at the balance point the design I've prototyped is money and has a super wide slalom action at all speeds including a huge wake at slow speeds. To keep everything happy the weighting on this thing has to be in a pretty tight window no more than 1/10th of an ounce variance....I am trying to get to a point where with careful measurements and precise weighting that the final weight is in that narrow window consistently without any further steps.

So instead of trying to super lighten the resin and introduce all kinds of extra steps I'm going to take a stab at the 16lb. foam. If it truly is lighter than basswood and has reasonable durability I should be able to achieve my goal and keep my sanity.... the devil is in the details though so I'm not counting my chickens before they hatch...

Thanks for the input vodka man...

John

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I had the same problem making wake baits. So now I use the resign and MB mixture like you stated but I fill my mold with chopped up cork. then I take a large syringe and inject the mold. Still leaves some voids and such but a little wood filler and you are good to go. Also you have to have a mold that has good air escapes or you will have lots of defections. I dont know if this get it light enough but it really lightens my baits. Dave and I may do some experiments doing this with balsa if we get time but the reason I think cork works so well is that it doesnt absorb moisture. Good luck!

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Hey Matt,

Thanks for the response, the more input the better. I'm really not sure why my foam experiment failed so miserably....it didn't absorb any moisture but it prevented the mold from pouring completely. I may have let the pot cure up too much and that prevented a good poor. The only problem I have with the idea of putting chopped cork, balsa, or foam in the mold is that I suspect its going to be really difficult to control the finished density down to the tolerances that I'm looking for. I suppose if you have an accurate way to measure the amount of material going in then it could be controlled but the chopping method is creating pieces with semi-random volumes and surface areas so being consistent from bait to bait could be a challenge. If you started with a 1"X2" piece of foam and chopped it, would it still displace the same volume as it did when it was a single piece?? (I'm not sure) I'm going to back of of my MB's a little to increase the flow in my mold and try the foam again just to verfiy what the issue was. I'm already adding MB's to featherlite resin so you can see how far I'm trying to go to get the buoyancy back. Theoretically you could nearly eliminate the MB's (although I like the sanding properties) and rely on your core materials for weight reduction. I wish I was skilled enough to figure out how to create a hollow void where the ballast weight goes that could be accessed with a threaded cap that way the thing could be micro-tuned after the fact to adjust for anglers preference, colder or warmer water, etc.

As far as the balsa, I bet it could work with some precautions to seal it just long enough to get through the cure. A quick roll in some 5 minute epoxy. One of my favorite production pencil poppers is the Yozuri surface cruiser. It is obviously a molded bait but they really nailed the proper buoyancy....its super bouncy and light in the front end....and durable. They refer to it as a poly balsa urethane.....sounds like resin over some sort of balsa core to me.

I'll keep you updated on my trials and any additional input is always great!

Thanks.

John

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Hey Matt,

Thanks for the response, the more input the better. I'm really not sure why my foam experiment failed so miserably....it didn't absorb any moisture but it prevented the mold from pouring completely. I may have let the pot cure up too much and that prevented a good poor. The only problem I have with the idea of putting chopped cork, balsa, or foam in the mold is that I suspect its going to be really difficult to control the finished density down to the tolerances that I'm looking for. I suppose if you have an accurate way to measure the amount of material going in then it could be controlled but the chopping method is creating pieces with semi-random volumes and surface areas so being consistent from bait to bait could be a challenge. If you started with a 1"X2" piece of foam and chopped it, would it still displace the same volume as it did when it was a single piece?? (I'm not sure) I'm going to back of of my MB's a little to increase the flow in my mold and try the foam again just to verfiy what the issue was. I'm already adding MB's to featherlite resin so you can see how far I'm trying to go to get the buoyancy back. Theoretically you could nearly eliminate the MB's (although I like the sanding properties) and rely on your core materials for weight reduction. I wish I was skilled enough to figure out how to create a hollow void where the ballast weight goes that could be accessed with a threaded cap that way the thing could be micro-tuned after the fact to adjust for anglers preference, colder or warmer water, etc.

As far as the balsa, I bet it could work with some precautions to seal it just long enough to get through the cure. A quick roll in some 5 minute epoxy. One of my favorite production pencil poppers is the Yozuri surface cruiser. It is obviously a molded bait but they really nailed the proper buoyancy....its super bouncy and light in the front end....and durable. They refer to it as a poly balsa urethane.....sounds like resin over some sort of balsa core to me.

I don't think any of the additives will need sealing first, especially cork, which is primarily used for its resistance to liquids (wine stoppers). In any case, the sealing operation is only the same as putting it into the resin.

Using chopped additives can be controlled very accurately, with very predictable results, but you have to work in the metric system. Weight volume and density in metric units, all tie together very conveniently and with numbers that make sense. If you know two of the three numbers, the third can be calculated.

The weight is easy with a gram scale. With the fine controls needed for your project, you should already own a gram scale, if not, it should be high on your shopping list.

Everything can be calculated, using only a ruler, a gram scale and a simple calculator. One piece of information you do need to work out, is the volume of your lure. This too is very easy to do. If you want to know more about this, PM me your email addy, 'cos if I write too much techy stuff here, some members get upset.

I ballast all my lures using numbers, the first float test my lures get, is after the final top coat has cured, even suspended lures.

Dave

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I don't think any of the additives will need sealing first, especially cork, which is primarily used for its resistance to liquids (wine stoppers). In any case, the sealing operation is only the same as putting it into the resin.

Using chopped additives can be controlled very accurately, with very predictable results, but you have to work in the metric system. Weight volume and density in metric units, all tie together very conveniently and with numbers that make sense. If you know two of the three numbers, the third can be calculated.

The weight is easy with a gram scale. With the fine controls needed for your project, you should already own a gram scale, if not, it should be high on your shopping list.

Everything can be calculated, using only a ruler, a gram scale and a simple calculator. One piece of information you do need to work out, is the volume of your lure. This too is very easy to do. If you want to know more about this, PM me your email addy, 'cos if I write too much techy stuff here, some members get upset.

I ballast all my lures using numbers, the first float test my lures get, is after the final top coat has cured, even suspended lures.

Dave

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Well I ran several trials using the chopped foam today and it was unsuccessful. I did get the mold to pour by mixing the foam in the mix however I ran into other problems. Even with massive amounts of the chopped foam my final weight dropped insignificantly. The only explanation I can arrive at is that the resin is chemically breaking down the foam and collapsing it thereby eliminating much of my weight reduction. Apparently cork seems resistant to this process so I may try the cork as an alternative as I await my shipment of 16lb foam. After thinking it through I can see how the additives can be controlled through using my gram scale (yes it tells me all about my failed attempts!! HA!)

I am still confident that with a mix of featherlite and cork or 16lb foam that I will get what I'm after. The good news is that my mold is performing well and showing no signs of wear at this point. I am hopeful the foam solves my density problems. In an ideal world I would love to be able to just insert my ballast weight and pour resin (foam) and be done. I track the weights of the raw blanks before any hardware, ballast, paint and clear and then weigh them again to see how much weight I'm adding by the final product. Your right though, the finest details can change the whole formula....I just switched screw eyes and my new ones weigh half what the old ones do shaving .15 oz off my finished lure- weight that I will have to add back into the equation. Fortunately the lure performs better and better as the ratio of ballast to overall weight increases. I'm shooting for a nearly 50/50 as my target. The action is enhanced with lower density at the ends which seems to cause it to rotate harder at its balance point where I have it weighted. I guess you would call it a fulcrum effect. I got the volume of my mold cavity by filling it with water and then measuring it....it came out to about 5 fluid oz. Its a 7" cigar shaped lure with a greatest diameter of 1.25".

Thanks for the input and keep it coming...

John

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John,

I have had a similar problem with resin baits and have a solution that has worked for a top water chugger, which may help you with some tinkering on your part. I have also used the micro balloons with good success but wanted another option.What I have done is created an air cavity in the bait to add additional buoyancy and an additional rattle cavity. I took several resin blanks from one of my finished molds and used a dremel tool to create a cavity on the underside of the blank. After much tests i finally found the right size cavity and then made a 2 piece mold of the blank with a cavity. This way i did not have to use the dremel tool every time a blank came out of the mold to create the cavity. I then took a blank without the cavity and made a half mold of the bottom of the blank using the play dough type fast cure mold material. So this mold is only the bottom half of the lure. So i make the blank with the cavity and clean it good with denatured alcohol. Then i mix some more resin and pour some into the bottom of the half mold and then press the blank with the cavity on top of the liquid resin and this creates an air cavity and in the case of the topwater chugger I simply take a steel shot and hold it to the top of the blank (before placing it in the second mold) with a strong magnet. When it dries i have a cavity for additional buoyancy and another rattle chamber. This is a few extra steps and the placement of the screw eyes, which i prefer over a through wire design, needs to be considered. There is also some additional sanding involved which i don't mind as it is a much faster process than carving and sanding wood, which i have done for years until I recently discovered resin and molds. I have only recently started this process on the top water plug and over time i hope to improve the process. I hope i have explained this well and that it helps.

Jim

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John,

I have had a similar problem with resin baits and have a solution that has worked for a top water chugger, which may help you with some tinkering on your part. I have also used the micro balloons with good success but wanted another option.What I have done is created an air cavity in the bait to add additional buoyancy and an additional rattle cavity. I took several resin blanks from one of my finished molds and used a dremel tool to create a cavity on the underside of the blank. After much tests i finally found the right size cavity and then made a 2 piece mold of the blank with a cavity. This way i did not have to use the dremel tool every time a blank came out of the mold to create the cavity. I then took a blank without the cavity and made a half mold of the bottom of the blank using the play dough type fast cure mold material. So this mold is only the bottom half of the lure. So i make the blank with the cavity and clean it good with denatured alcohol. Then i mix some more resin and pour some into the bottom of the half mold and then press the blank with the cavity on top of the liquid resin and this creates an air cavity and in the case of the topwater chugger I simply take a steel shot and hold it to the top of the blank (before placing it in the second mold) with a strong magnet. When it dries i have a cavity for additional buoyancy and another rattle chamber. This is a few extra steps and the placement of the screw eyes, which i prefer over a through wire design, needs to be considered. There is also some additional sanding involved which i don't mind as it is a much faster process than carving and sanding wood, which i have done for years until I recently discovered resin and molds. I have only recently started this process on the top water plug and over time i hope to improve the process. I hope i have explained this well and that it helps.

Jim

I get what your saying and I've considered something similar if I come up empty adding cork to the resin or using straight 16lb. foam. This particular lure doesn't really move in a way that would lend to adding a rattle chamber but the idea of creating a void has definitely crossed my mind. I was thinking I could create an air chamber by placing a hollow plastic tube in the cavity (sealed on both ends)...it could be secured to the ballast weight to keep it in place. I believe it would just be a matter of figuring out the exact size of the tube. I can see at least 3 or 4 routes to go here with the 16lb. foam being the simplest and cleanest solution in theory. Sounds like I will have to be careful with the volume with the foam as it expands 4 times by volume but that shouldn't be hard to calculate knowing that my cavity holds about 5 oz.

Thanks for taking the time and nice to know I'm not the only one who's wrestled with these issues.

John

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I get what your saying and I've considered something similar if I come up empty adding cork to the resin or using straight 16lb. foam. This particular lure doesn't really move in a way that would lend to adding a rattle chamber but the idea of creating a void has definitely crossed my mind. I was thinking I could create an air chamber by placing a hollow plastic tube in the cavity (sealed on both ends)...it could be secured to the ballast weight to keep it in place. I believe it would just be a matter of figuring out the exact size of the tube. I can see at least 3 or 4 routes to go here with the 16lb. foam being the simplest and cleanest solution in theory. Sounds like I will have to be careful with the volume with the foam as it expands 4 times by volume but that shouldn't be hard to calculate knowing that my cavity holds about 5 oz.

Thanks for taking the time and nice to know I'm not the only one who's wrestled with these issues.

The foam will solve your density issues, but there will be a learning curve with this stuff, do not expect to get perfection straight away. I am not sure if it needs a release agent with RTV. Hopefully someone else will jump in here with some suggestions, but you should do some searches and read up some before starting. Also, start with a junk mold for practice, don't risk your prize mold until you have experience.

Man, those screw eyes are heavy. Maybe you should have a go at twisting your own, if you want to save some more weight.

Flounder1, interesting solution.

Dave

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The foam will solve your density issues, but there will be a learning curve with this stuff, do not expect to get perfection straight away. I am not sure if it needs a release agent with RTV. Hopefully someone else will jump in here with some suggestions, but you should do some searches and read up some before starting. Also, start with a junk mold for practice, don't risk your prize mold until you have experience.

Man, those screw eyes are heavy. Maybe you should have a go at twisting your own, if you want to save some more weight.

Flounder1, interesting solution.

Dave

ro

Thanks for keeping an eye on the thread Dave. I am definitely looking forward to my trying the 16lb foam. From the research I've done the main considerations are mixing and pouring quicky as it sets up real fast and starts the expansion process. Also, I've read that there is a potential to blowout your molds if its overfilled and there isn't sufficient venting. I have a few quarter inch vents and my sprew is pretty large-nearly 1/2" so I think I should be ok as long as I don't overdo the volume. I like your suggestion of using a scrap mold to get a feel for it. My source is UPS from North Carolina so I'll have to be patient. My old screw eyes weighed .1 oz each the new ones are .05 so I saved weight. .15 oz between the three that attach to the lure. The strategy with this lure is to have a very light body and heavy fulcrum weighting. 1.7 oz body weight w/ 1.5 oz fulcrum weighting for a total weight of 3.2 oz before paint and hardware.

Would love to hear from anyone else with experience using 16lb. foam......

John

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John-with regards to the tube I have tried this in the past but have been unable to properly seal the ends. What i have tired is a very small PVC pipe and you can actually suspend this in your mold with fishing line. The tube is attached to the line with clear medical tape that is sold a any drug store. This is how I put rattles in the resin baits that i make. The rattle is the same PVC but is plugged at one end with steel shot (for a sling shot), a bb is then put in the other end and then the open end is plugged with another steel shot. This adds a lot of weight but i have figured out the right micro balloon mix for the resin for the molds that i have made. This works for me because i make my 2 piece molds with the lure sitting up right. The bottom section of the mold is the bottom portion and the top section of the mold is the top part of the lure with the bottom section usually a little larger. This way i can take the open mold and the rattle or in your case the air tube that is attached to the fishing line and suspend it in the mold. Small slits with an exact o knife create a nice channel for the fishing line at each end of the mold. Pull the line tight wiht large clips put the top half on and then pour. This has really worked well for me and may hopefully lead you to a solution.

Dave-you are correct about the weight of the screw eyes and to be honest at first i tried the through wire and had some difficulty. I do need to figure this out with regards to top water plugs. The only problem i would see is that often my lures out of the mold require some sanding and some filling of holes due to air pockets which i think the MB's contribute to. This i don't mind as the entire process is much faster then carving wood. I have felt that the wire would be in the way of sanding the lure. I feel that i am making pretty good molds and made a large improvement several months ago when someone posted a tutorial on the subject, but have to admit i continue to learn and this site has been a great resource. Jim

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Ran some trials with the cork today. Way better than the foam tests. You can achieve much more weight reduction than with MB's alone thats for sure. I took a blank thats normally about 2.95 oz using featherlite alone and was able to drop it down to 1.8 using corking additive. The amount I used was obscene and even though I got very close to the weight reduction I'm after it did create a fair amount of voids and air pin holes in the outer core. Kind of a messy solution only because of the massive weight reduction I'm trying to achieve....nearly 50% less than featherlite. However, if your maxed on microballoons and need to pick up another 20 or 30 percent the cork can easily get you there. For me, it just proved that I need to wait (patiently...and I'm not) for my 16 lb. foam to arrive. Anyone have any local sources in So Cal for 16lb foam.....my searches turned up nothing so I'm waiting for a shipment from North Carolina.....

Still no foam guys out there? I know some Musky guys are using it which is really encouraging based on the amount of abuse those fish dish out....

John

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Ran some trials with the cork today. Way better than the foam tests. You can achieve much more weight reduction than with MB's alone thats for sure. I took a blank thats normally about 2.95 oz using featherlite alone and was able to drop it down to 1.8 using corking additive. The amount I used was obscene and even though I got very close to the weight reduction I'm after it did create a fair amount of voids and air pin holes in the outer core. Kind of a messy solution only because of the massive weight reduction I'm trying to achieve....nearly 50% less than featherlite. However, if your maxed on microballoons and need to pick up another 20 or 30 percent the cork can easily get you there. For me, it just proved that I need to wait (patiently...and I'm not) for my 16 lb. foam to arrive. Anyone have any local sources in So Cal for 16lb foam.....my searches turned up nothing so I'm waiting for a shipment from North Carolina.....

Still no foam guys out there? I know some Musky guys are using it which is really encouraging based on the amount of abuse those fish dish out....

I think the only way to improve the cork mix from where you are now, is to use a vacuum unit to remove the air. Hardly worth it as you are moving to foam. Good luck with that.

Dave

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Vents in your mold and an injector help with the imperfections. I goto the local hospital supply and buy the biggest syringe they have with a cathedar tip. then just draw the resin in and inject into the mold and let it spew out the vents. you will have a few spots to fill with filler but a quick sand and epoxy coat later and your good to go.

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Well, after a long wait got my 16lb. foam today. Played around with some junk molds to get a feel for it. The material expands about 4X's its liquid volume and hardens up pretty quick. Right off I could tell the lightness was there...between balsa and basswood is accurate. As far as toughness goes it seems on par with wood thats for sure from just handling it.

The challenge....getting a good casting. I prepped my RTV mold and did a pour of approx. 1/4 the volume of the cavity. The material expanded slightly more than 4X's or my calculations were off a little bit' and the expansion literally pushes the mold apart slightly and of course caused the cast to be massively distorted. I tried multi-pours and ended up with voids...The best I got was with a single pour that got close to the exact volume of the cavity but it still seems that no matter what I did the material wants to exert significant pressure on the mold walls thus separating at the mold halves slightly. (Causing distortion). It pretty much seemed liked a certain amount of pressure has to be withstood by the mold in order for it to produce an accurate detailed casting and completely fill the cavity without voids.

It pretty much seems like for the foam to work in the confines of a mold cavity the mold itself has to be able to withstand a fair amount of expansion pressure without moving or bending....it seems that silicone doesn't lend itself well to this as it wants to flex which is fine for urethane resin but not so much expanding foam.....learning curves...learning curves....so tempting to return to wood but honestly I am really impressed with the density properties of the foam...its essentially plastic wood....and the other production possibilities that molds open up.

So my solution....build a mold from bondo (rigidity)....add more vents to the mold (more avenues for escape).....use clamps instead of rubber bands while casting the foam to withstand the expansion pressure and prevent the mold halves from seperating under the pressure. I feel like I'm in uncharted waters at this point....if anyone has any experience or suggestions please don't hesitate.

John

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You need to experiment with vent holes, to give the expansion excess somewhere to go. Position of vent holes and size. You will probably need multiple vents, to prevent voids. Two load spreader plates for each face on RTV molds, with clamps, will help prevent distortion.

Temperature is a factor on the expansion. You may not have much control over temperature, but you should at least keep notes of the temperature, along with all the other variables.

Mixing introduces the air into the foam, which also affects the expansion and the final density. You need consistency for your baits, so you need to find the mixing speed that produces the best foam for your application. Make a note of it and mix the same speed, for the same duration every time.

The amount that you mix can be finely controlled, using a gram scale. This will promote consistency and also prevent you wasting product. Again, make notes for every pour, at least until you get the technique cracked.

Keeping records of every pour is a pain, but is guaranteed to shorten your learning curve with this temperamental product. Spreadsheets are a very good way of keeping control and after a dozen or so pours, you will start to see a pattern in the numbers. This will help you predict the solution. This is especially useful when you start pouring a new mold, as you can refer back to figures for previous molds for direction.

Weigh the foam bait and weigh the expansion scrap, these numbers will give you a ratio of how much you need to reduce the weight of the next attempt.

It is all down to your character. You may be a 'wing it, seat of the pants' type and loath record keeping. In that case, you are in for a hard ride. Keeping records is a good habit. If it helps you out, I can put together a spread sheet for you. If you don't own a gram scale, it might be a worth while investment.

I hope these random thoughts give you some ideas to try.

Dave

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So my solution....build a mold from bondo (rigidity)....add more vents to the mold (more avenues for escape).....use clamps instead of rubber bands while casting the foam to withstand the expansion pressure and prevent the mold halves from seperating under the pressure. I feel like I'm in uncharted waters at this point....if anyone has any experience or suggestions please don't hesitate.

Careful with the rigid mold material. I have not tried resin for the foam casting mold, but I did try PoP. What a disaster. The mold halves were well locked together and the mold had to be scrapped. You may have more luck with a resin mold, as it can take more abuse.

Have a plan for how you are going to pry the mold open and what you are going to use. Build suitable leverage grooves into the mold. Make the mold slightly deeper than normal. This will help prevent snapping the mold, should you have to use excessive force.

Start off with over the top release agent, maybe a thickish smear of wax, then work your way back. This way, you can tune in to the ideal release compound layer, without compromising your mold.

I am sure I will think of more ideas. I am hoping that some experienced foam users will jump in and help too.

Dave

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Careful with the rigid mold material. I have not tried resin for the foam casting mold, but I did try PoP. What a disaster. The mold halves were well locked together and the mold had to be scrapped. You may have more luck with a resin mold, as it can take more abuse.

Have a plan for how you are going to pry the mold open and what you are going to use. Build suitable leverage grooves into the mold. Make the mold slightly deeper than normal. This will help prevent snapping the mold, should you have to use excessive force.

Start off with over the top release agent, maybe a thickish smear of wax, then work your way back. This way, you can tune in to the ideal release compound layer, without compromising your mold.

I am sure I will think of more ideas. I am hoping that some experienced foam users will jump in and help too.

Dave

Thanks for all the input Dave. I really appreciate your consistent, quick feedback. I have thought of much of what your suggesting. I did manage to get one "decent" pour since my last post so I remain hopeful. I was right on target with my weight goals so I will performance test the foam lure tommorrow to verify that my weight distribution ideas are on target. I do own a gram scale which I primarily use to verify lure weight. That is an eye opener to realize that the expansion rate is affected by temperature and how much air is introduced during mixing.......once I get a handle on pouring clean castings I will have to see how much variance temperature and stir method cause in final density. I think I will take your cue and use spreader plates with the silicon mold in conjunction with adding some additional venting and see how that fairs. I try to keep things simple as possible but I will take to heart keeping notes on key variables to keep a better handle on outcomes.

I will hopefully have things narrowed down in the next few days.

John

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Thanks for all the input Dave. I really appreciate your consistent, quick feedback. I have thought of much of what your suggesting. I did manage to get one "decent" pour since my last post so I remain hopeful. I was right on target with my weight goals so I will performance test the foam lure tommorrow to verify that my weight distribution ideas are on target. I do own a gram scale which I primarily use to verify lure weight. That is an eye opener to realize that the expansion rate is affected by temperature and how much air is introduced during mixing.......once I get a handle on pouring clean castings I will have to see how much variance temperature and stir method cause in final density. I think I will take your cue and use spreader plates with the silicon mold in conjunction with adding some additional venting and see how that fairs. I try to keep things simple as possible but I will take to heart keeping notes on key variables to keep a better handle on outcomes.

I will hopefully have things narrowed down in the next few days.

John

I am so glad that you are making progress with this material. I would have felt so bad if I had wasted your money with mentioning foam as a solution. But it sounds like you have the tenacity to crack this one and I look forward to your reports and pics.

I went ahead and did a simple spread sheet, just for fun. If you want it, pm me your addy.

Dave

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I have not tried this specific foam, so I can't speak from experience about it.

But I've used expanding structural foam for years in construction.

Since rigid molds are such a pain with rigid materials, and your RTV mold seems to be good, I'd try to make the RTV work before I went to a rigid mold.

I'd mount plywood backs to my RTV mold halves, or even set them in wood box halves with more RTV to make the assembly clampable, and clamp the halves together with wood clamps.

I'd add additional 1/4" minium vent holes in the top of the mold, and see if I couldn't get the RTV mold to work.

From my experience with expanding foam on the jobsite, it will "relieve itself" through the vent holes if it can't go anywhere else.

And removing the overage is a lot easier that trying to pry a rigid work piece from a rigid mold.

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I have been playing around with cork and other additives as well. But a couple other options I have been using or a while are

1) if the bait is 1 piece you can use resin (with no mb) and "roll" the mold when adding resin to create a very hard outer shell. Then add 610 foam to the inside of the bait to create a very buoyant bait. This process requires a wire harness being molded into the bait. I believe Larry Dalhberg has a video of this process on his website. he does it for his whopper ploppers.

2) I regularly pour baits with resin/mb mixtures then drill out parts of the bait and fill them with 610 foam. This works great as it allows me to be very consistent with the buoyancy of the bait as I can control the resin/mb mixture and can drill out the exact same amount each time for the 610 foam. Also the bait stays very strong and hard. Areas where screw eyes are screwed in are not weakened.

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I have been playing around with cork and other additives as well. But a couple other options I have been using or a while are

1) if the bait is 1 piece you can use resin (with no mb) and "roll" the mold when adding resin to create a very hard outer shell. Then add 610 foam to the inside of the bait to create a very buoyant bait. This process requires a wire harness being molded into the bait. I believe Larry Dalhberg has a video of this process on his website. he does it for his whopper ploppers.

2) I regularly pour baits with resin/mb mixtures then drill out parts of the bait and fill them with 610 foam. This works great as it allows me to be very consistent with the buoyancy of the bait as I can control the resin/mb mixture and can drill out the exact same amount each time for the 610 foam. Also the bait stays very strong and hard. Areas where screw eyes are screwed in are not weakened.

I really like this second idea a lot. What is becoming quite apparent to me is whether its foam or featherlite resin....things like temperature and other environmental factors creep in and change the very thing I'm trying so hard to get a handle on. I think I see the end here with the addition of your suggestion. I could pour my baits with my lightest version of featherlite and mb's w/my ballast weights inserted. Smooth and tough castings. Weigh plug and determine how much material needs to be removed and replaced with foam. Can easily create some simple math to determine diameter/depth of hole to weight savings calculations. The answer has been right in my face with the foam.....I can see that with this system I can absolutely control final weight regardless of any other variables that creep in along the way.....

Vodka, thanks so much for your assistance and I don't regret at all getting my feet wet with the expanding foam. It looks like a found a use for it. Obviously I will have to drop down in density to get the weight savings I need using the removal method suggested to me. I feel absolutely confident that this process will work and allow me to get the tight weight tolerances I am after.

Do you think 2lb. foam used as a filler is too light or should I opt for the 3 or 4....hahahha...never ends....these details are minor ...I will post my final results on the prototypes...

Thanks everyone for their input...I'm mighty close now...

John

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