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Sealing Plastics Crankbaits
7 replies to this topic
Posted 15 March 2011 - 11:19 AM
OK, I need some help. I just started with casting plastic cranks from alumilite white and believe I will airbrush them with Createx. Do I need to prime the lures first and do I need to seal/topcoat them with something after painting? Your advice would be greatly appreciated, thanks.
Posted 15 March 2011 - 12:24 PM
I havent used alumilite but I have used a couple other resigns... This is just what I have found.... When using micro ballons in a 1 part ballons to 1 part A and 1 part ballons to 1 part B mixture it made the resign somewhat "soft" and had microscopic holes all over. So I sealed the lures with a 2 part epoxy of your choice (I use devcon 2 ton thinned with DA) then sand to get good adhesion and paint. Lastly Topcoat again with topcoat of your choice... for topcoat I like 2 coats of Etex for resign lures.
Now I use half the amount of ballons and fill my mold with chopped up cork.... then inject the resign. It leaves a lot of imperfections but makes a much more bouyant and stronger bait. I then proceed to do the rest the same.
Posted 15 March 2011 - 01:03 PM
I never tried the alumilite. I did micro balloons with polyester resin and very heavy on the MB's. So heavy that I could not pour, but had to inject the paste.
I never had any problems with paint adhesion. I scrubbed the bodies with dish washing liquid and a scrubber, to remove all traces of release agent. I lightly sanded to scuff up the surface, to give the paint something to grip onto. I would then apply spray can white.
I no longer use spray can whites, as they gave me fish eye problems with the D2T top coat. There is a product called bulldog adhesion promoter, that some of the top builders use. Might be worth exploring.
Posted 15 March 2011 - 08:35 PM
Alumite lures have many small holes that have to be filled before painting. You may not see them, but they are there! This is especially true if you sanded the lure after removing it from the mold - sanding breaks open micro-balloons on the surface. I agree with Matt about using a coat of epoxy (thinned with denatured alcohol) to fill all those holes. Maybe a water based sanding sealer would also work (haven't tried it) but I would shy away from anything containing a petroleum based solvent that might melt the Alumite.
Yes, you do have to topcoat the lure after painting. That's to keep the paint from being worn off the lure, or being dissolved by water if you used water based acrylic paint.
The problem I have with Alumite is that it requires lots of micro-balloons or SOMETHING to make it as buoyant as I need a lure to be. I hear that lots of micro-balloons thickens the mix and makes it hard to mold. Neat idea Matt about putting in shredded cork! But are you able to control how the cork is distributed while you inject the mix? I make bass baits which tend to be rather small and the problem with buoyancy was the real killer to me. I dropped the idea of Alumite after a friend sent me some samples with max micro-balloons based on a 2 1/4" D-bait copy. The blanks were just too dense and would barely float after adding hardware and finish. I'm just a hobbiest, so have no need for "volume production" and didn't explore it further. But if I did, I might be thinking along the line of trying to mold bodies from 16 lb foam to get buoyancy. 16 lb/cu ft density equates to hard balsa, which is more like it.
Posted 15 March 2011 - 11:24 PM
I found the same as you. The lowest I ever got the density was 0.65gm/cm3 (40Lb/ft cu) and that was the consistency of English mustard. I was thinking that something was wrong with my MB's, as everyone else was raving about how light their baits were.
Posted 16 March 2011 - 10:46 AM
It's kinda tedious but I hand cut the corks with a kitchen knife into little cubes. I molded my first baits so that they sit like they would in the water. Thus they sit upright in the mold. I was thinking that the cork would rise to the top and it would balance out for me being denser on the bottom... I found with the mixture of micro ballons I do this isnt the case as the mixture is still fairly thick and I prefer to inject it with a large cathader tip syringe ($2 at my local hospital supply). It seems that once I inject the cork doesnt move too much and gives me a pretty bouyant bait that is much stronger than if I used more micro Ballons. The draw back is I have A LOT of imperfections to fill on every bait.
Since my earlier experiments now I just use PVC pipe to mold baits in like one of the tutorials. PS, works great!!! Then once the bait is molded I inject the resign into the tail section. I dont care about how they sit as i found it doesnt matter that much... Once I weight and put hardware they sit and run perfect. I do this method on my crank molds but they are fairly big at a little over 3 inches. I can mold a smaller one and try it if you like Bob, but i would imagine it should work fine.
I have to admit though in one of my posts about a year ago Rookie coughed up the secret of using cork and not MB in his resign baits. He didnt go into detail about how it was done or anything but me living an hour from Napa I knew i had to try it... every time I go wine tasting now I ask for some corks and I get a bag full from everywhere. I have atleast a 5 gallon tub chocked full ready to be chopped up. If anyone has a better way please let us know... Or Rookie can you devulge any info on your process?
Posted 16 March 2011 - 11:50 AM
The density of cork is between 0.2 and 0.24gm/cm3. The density of the lightest balsa (model aircraft material) can be as low as 0.08gm/cm3. This means that you could easily double your buoyancy from your additives by using balsa.
Working with light balsa is a lot easier than cork and it is supplied in more convenient shapes and thicknesses. It is not the cheapest source of balsa, but cost per lure should be fairly insignificant.
Posted 16 March 2011 - 12:45 PM
Man I hate to hijack this thread maybe we should make a new one?
Dave I had the same thoughts but my early tests with balsa didnt go very well. I think I may have screwed up a variable and just never tried again... But it seemed that the same amount of balsa compared to cork was less bouyant. I thought at the time it was because the balsa somehow took up the moisture in the resign or something and once it did lost its bouyancy wheras the cork naturally repels water... I dont know and I should probably try some experiments again as my old theory sounds goofy now that I think about it.