[mike_in_indiana]

Im curious about the density and durability of the 2 part urethane foam. How does it compare in weight to balsa wood? And, is there any particular brand that seems to work better than others? Any comments or opinions would be greatly appreciated, thanks fellas.

[luresmith]

I routinely use two pack urethane resins for all types of crank making. There are plenty of brands out there that are very close in density and strength to balsa, in fact some are slightly better in terms of durability. Like balsa, you need to use a through wire, as screw-ins won't hold reliably in this type of resin. What you are looking for is a resin in which the two parts are mixed in equal quantities and foam then cure to form a rigid foam approximately 3 times the volume of the original components. Any large resin distributor should be able to help with this - I've bought it at the local hardware store before. There are a few simple tricks that can be used to increase the overall density or change the weight distribution of your crank, experimentation is the key.

I can point you to some pretty specific literature on this very subject. If you need further info, just zap me a personal message.

Regards
Greg

[Hiro]

I buy 2 part urethane foam from a Japanese company making chemical products. The urethane foam I use is much harder than the balsa wood and as hard as some hard wood. It has the higher buoyancy than the balsa wood. I think the material is very durable and good for saltwater plugs.

[redg8r]

Hi Mike,
I bought a gallon from Smoothon.com
its a 2 part (1:1) expanding foam.

mix equal amonts, a lil goes a long way. I use about a teaspoon worth for a bait.

[mike_in_indiana]

Thanks guys, for the insights on the urethane foam. Im hoping that next weekend I will have a little extra cash to start getting the supplies i need. Looks like the RTV mold making compound I will have to order since I cant find it anywhere in my area, and the urethane foam I can probably get here since there are plenty of marine shops around.

I have about 6 different balsa plugs made to use for masters on making the molds, Ill try to snap some pics of them and put them up this evening or tomorrow...( been busy runnin all over the place). All of the plugs Ive carved so far are topwater style baits. I figured Id keep it simple starting out. I plan on recreating some of the old antique plugs also, already have small, and medium sized "Bass Oreno" style plugs carved to serve as masters, a couple bodies for straight in-line stick type prop baits, and two popper type baits with one resembling a Hula Popper with a longer body.

I also have an original "Heddon Vamp" body and a "Midget River Runt" body that were in real sad shape and missing all the hardware that Im gonna play around with and see if I can make molds of them also.

[RiverMan]

Hello Mike,


I can't add anything that the "experts" above have not told you already but wanted to provide you with this link that Hiro put together. I think you will find it most educational.

http://www2.sala.or.jp/~hiro/making7e.htm


I have been toying with the same things you are talking about for many months but have never gotten further than that. I did build about 20 Heddon Tadpolly's a year or so ago that turned out very good. Make sure that you take into consideration plug balance as this is one thing I didn't think about in the beginning. Throw any plug into the water and see how it balances, they simply will not swim as you would like them to unless the balance is correct. Crank-baits must have a "bill down" resting position or they won't swim/dive correctly. There are others here with far more experience than I that can help you with this.

The biggest drawback with all of this is the silicone molds, somewhat spendy to build. The "luresmith" as told me that resins work for him but I have had some serious problems with bubbles while using this product. Let us know how things go, I would be very interesed. Good luck to you!

RM

[luresmith]

Hey Riverman,

What resins have you tried for your molds? I have very few problems with bubbles using epoxies, and the odd bubble that does occur (maybe 1 minor bubble in 5 molds) is easily filled. I prefer this style of mold for expanding urethane foams for a couple of reasons: 1) they cost about 1/10th as much, 2) you can get the resin anywhere and 3) In my experience they work better than RTV silicone with this type of resin. They are also very durable. On the down side, you need to use a mold release, which adds a little extra time to the process and isn't necessary with RTV's.

As a bonus, I can make a mold and start using it in the same afternoon, no waiting 24 hours for the RTV to cure.

Cheers
Greg

[robalo01]

For smooth baitls with no undercuts, try a auto body filler (bondo) mold. For more complex shapes, try a household silicone mold catalized with water. Do a search in the soft plastics forum for this. I would like to ask g8tr if the "clamshell" mold could be used for polyurothane fome.

[redg8r]

The household silicone is pretty much the same as RTV, without the platinum, tin, or whatever catalyst is used on your brand of RTV.

I dont think my clam mold tutorial would fare well with rigid expanding foam....2 reasons:
[1] The mold needs vented, or the pressure will deform the soft mold.
[2] The mold has a thin wall where you extracted the master body.

if you add those 2 issues together, your better off with a normal 2-part mold.

I'm curious as to what the luresmith recommends as a mold release for urethane?? I havnt found a good one yet.
Also, how do you do 2-part resin molds without shrinkage? If I could takle that issue Id throw my RTV out the door
Very interesting.

I have to important No-NO's for ya if your usin rigid foam.
[1] Urethane rubber molds, I fused a few of em before I gave up.
(maybe if I used a suitable release it would have worked) I used a wax based release & it was useless.

[2] Use gloves when using the foam, I got some on my hands & literally had to "sand" it off, its very sticky stuff. Acetone works before it sets up, but if it cures on your skin.......

Thanks guys

good luck fellas

[luresmith]

Hi Red-g8r

I've had excellent success using a beeswax based furniture polish as mold release on epoxy molds. The first time i use the mold I apply it very liberally with a toothbrush, leave it sit for 20 mins or so, then buff off with a soft cloth. Then I thin some wax with mineral turpentine and immediately before each pour i wipe a thin layer over the mold cavity. It's pretty rare I have one stick. After the cranks have set i drop them in acetone for up to 24 hours to soak off the wax before painting.

You're right about getting the stuff on your hands. There's another good reason to keep resin off your hands too - urethanes are pretty safe compared with eg polyesters, but they do contain isocynates. Read the MSDS, best to keep the stuff away from bare skin. I have an environmental chemistry background, so perhaps I'm over sensitive, but I want to see my kids grow old.

With regards shrinkage, perhaps I've been lucky with the brands I use, but I haven't had a great deal of trouble. For much of my work fine tolerances aren't important anyway. Here's a few tips that may help though:

If you are making a fairly large or thick mold, consider building it up in layers. smaller volumes of esin means less heat and less shrinkage.

Use smaller volumes of catalyst. This means that your molds take longer to cure, but helps reduce shrinkage.

Persevere, persevere, persevere!!!

Incidentally, I've had some success using 'clam' style RTV molds for expanding foam cranks. The trick is to work out how much resin you need and make sure you don't have too much excess. There is a tendency for some distortion about the seam line. Personally I prefer epoxy for the reasons I've stated above. The major disadvantage of epoxy is odour - work in a well ventilated place.

Regards
Greg

PS Red-g8r, I'll send you a PM - interested in your comments and feedback on some stuff.