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What foams and how long to expand
4 replies to this topic
Posted 21 January 2005 - 07:13 AM
A couple of quick questions about foams
1) Any one use 8lb foam? its supposed to be similar to balsa?
2) Once mixed how long do foams usually take before they start expanding?
Would a person have time to inject several molds using a syringe? I was thinking about mixing the foam in a cup and filling a large syringe before filling a mold, this way you would be able to controll the exact amount put into each cavity minimizing over pouring and also being able to use a smaller spru hole to get a tighter/harder shell on the body.
Posted 21 January 2005 - 07:26 AM
8lb is similar to balsa but i'd say it was denser and harder. The working time is appx 1 min. You don't inject foam you just pour it in. It will expand to fill the mold. You can pour it into several molds at once but you must be quick to join the 2 halves and clamps them tight. With 16 lb foam I found that by filling one side of the mold will be sufficient to get a complete lure. With 8 llb you'd need less as it expands twice as much as 16 lb.. The excess will come out the spew so it doesn't matter if you overfill. It will just be expelled.
I have a tutorial in the How to under hard baits. and Shopmaninc. com has the specs for the foams. As for spews with foam, start with about 1/8".
Posted 21 January 2005 - 08:41 AM
As a rule of thumb the poundage is the weight of an expanded 3ft x 3ft cubic block.
5lb 3x3 block = superlight with larger air cavities and thinner skin.
16lb 3x3 block = light with denser air cavities and thicker skin.
I haven't used 8lb but did try the 5lb as it seemed like a better choice in weight at the time. It expanded and cured well however the inner air pockets were larger (some peas sized) and it was very thin skinned. Regardless of sprue hole diameter the skin just didn't get thick. You can still collapse an air bubble just under the skin while foiling. Just wasn't tuff enough to work with. 8lb is not much more than the 5lb and I don't think you'll get the results you're looking for.
If this is your first attempt at foam lures I'd reccomend at least 15lb for the best structural integrity.
Posted 21 January 2005 - 05:47 PM
Husky, I read your tutorial earlier i's what got me thinking about foaming.
Wouldn't you pour the foam into the mold through the spru hole, such as you pour lead into a do-it mold?
Shawn, Thanks for sharing your experience with the foams. My plan was to use Tally's dip to base coat my lures thereby minimizing any soft spots prior to painting and using two polymer resin top coats. My reasons for the 8 lb was twice the foam for the same price as the 16 lb.
Posted 21 January 2005 - 05:57 PM
It's Not like pouring lead at all.You pour it into half the mold and then place the other half over it and clamp it shut(See Tut.). It expands, filling both sides, evenly. JMHO, but I see no reason to use anything but the 16 Lb Density. $48 will buy you 2/3 of a cu ft of castings if you get the 16 lb kit. Buying 8lb is false economy.