Sorry for the delayed reply, have been having eye surgery and have been partially blinded for a week or two.
Okay, so you've asked a lot of questions and raised a lot of points, I'll do my best to get through them one by one.
"Here in Korea there is not much bow building meterial" - you have plenty of good material in korea! Korea has one of the oldest & strongest archery traditions in the world, I wouldn't discount your local bamboo & timber combinations available.
"Do i need Colloidal Silica?"
"Why thickening resin? what is gap filling? what's the advantage of gap filling and thickening?"The silica just acts to thicken the resin, otherwise the resin is too thin (like water) and will flow out of the joint. For a long time I didn't use silica and it still worked, but I had a higher failure rate. Gap filling properties refer to the epoxy filling gaps between the surfaces, whether at a micron level or up to fractions of an inch. It just helps the bond make up for any imperfections (even at a very, very tiny size) in your preparation.
"what is the difference between bow making resin(like smooth on) and normal epoxy resin? concentration(thick) and gap filling?" There is many, many different epoxy resins out there, Smooth On is just one - one that is very strong & very thick/goo-ey. The thickness/goo-eyness is what gives it the gap filling properties. Epoxy Resin tends to be stronger than Polyester Resin, which I wouldn't advise using. While Smooth On is a great product, it's not easy to get everywhere in the world while other epoxies are. Generally speaking, any epoxy compound should be good enough to used at some level, but for high end bows make sure you've experimented with the compound previously. To make it clearer, the difference between an epoxy resin and an epoxy glue is really only the viscosity/thickness/goo-eyness.
"how about make fiberglass lam like this?"This is, basically, similar to the way I outlined using roving in the post on page 2 with the bad MS Paint picture. I would strongly suggest that if all you have is roving, you give that a try. If I had access to roving easily, I would probably be doing it that way.
Colloidal Silica and aerosil or fumed silica is same?They fulfill the same purpose in this application, but they're not the same.
in the link someone says Laminating fiberglass to wood it can be used without thickeners, but for wood to wood I would use one of the above agents to prevent gaps. is that true?Yes, it's basically what I've been saying through this entire thread.
and what about epoxy bendability or flexibility?It's not the epoxy doing the work, it's the fibreglass & wood. The epoxy is just the glue. Bear in mind that, for bowmaking, the 'flexibility' and 'bendability' are not a big deal, this is more for the aeronautical industry with huge bending wings and things like that.
talc is cheaper than sillica can i use talc?Maybe? I'm not an expert, I've just experimented with a few things and have some experience in some other industries. I would say it should probably work for this application.
how about milled fiber glass?This is colloidal silica. Silica = glass, colloidal = ground up very small.
in the video he says milled fiberglass give epoxy strength and flexbilityKinda, sorta. Yes and no. There's a lot of other variables.
you said fiberglass cloth won't be doing any 'work' when the bow is drawn, it will only be stopping splinters lifting. but when I added fiberglass cloth, draw weight increased. it just increase draw weight and not increase arrow speed(elasticity)?You've increased the second moment of area of the limb, so yes, you've increased the draw weight. Does this increase the draw weight as much as a proper prestressed lam? No. You could create a limb using only cloth & resin by building up layers of cloth impregnated resin and it would work. When I used the term "Work" in my original post I was referring to "Structural Work", which is an engineering term.
you said prestress fiberglass but it looks just straight fiber. pre stress means just lay fiberglass straight? no need to pull or stretch fiberglass strongly? just put fibers straight is enough? something like prestressed concrete?(rodlonq said) or just to hold fibers in the correct plane as the resin is poured(hunterguy1991 said)Prestressing means the fibreglass is straight and all in the same direction. It also means that any slack, or looseness, in the fibre is taken up already so that when it is put under load (as the limb bends) it immediately begins storing energy efficiently, like prestressed concrete. Basically, it's what they both said.
what is correct? use only woven fiber cause friction but mix ud fiberglass and woven fiberglass is ok?A mixture of the two is better than only using woven cloth, but unidirectional on its own would be preferable. To be honest, using fibreglass cloth directly on the timber as a backing is as efficient as using drywall tape, or brown paper bags, or silk, or linen, or something like that. Even rawhide, maybe. The guy who said "the woven glass tended to break down due to the friction of the crossed woven fibres against one another resulting in the fibres being severed" is correct, but you'd need to shoot the now several hundred thousand times for it to be an issue. He tends to have a very high standard for bow construction, despite not building bows himself. He is also very interested in very fine details, which is great for him, but very different to my approach of just getting the job done and learning new techniques.
Going through your posts you seem to be getting a lot of stuff very confused and mixed up. While this composites stuff isn't real easy, it's not real hard either. I do appreciate that English is not your first language though.
If you want to understand about why to prestress the fibreglass do some research into prestressed concrete - the idea of a matrix of concrete/resin and steel/fibreglass are the same principles. Look at some engineering texts or websites on this.
Don't get hung up (a phrase in english that means "interested too much" or "focused a lot") on the details. Ultimately, all these ideas will work, it's just a matter of how well and with what finish at the end. The best advice I can give you is to buy some materials and start experimenting. Or do an Engineering degree. It's cheaper to buy the materials though.
You should also read
www.poorfollbows.com. While Sam Harper doesn't make his own fibreglass lams and the only epoxy he uses is smooth-on, his approach to bow building and way of thinking about what he is doing will teach you a lot about how to move forward with your own bow building. I strongly advise you start with something simple, like a simple board bow, and move up to more complicated bows with fibreglass and wood lams, or bamboo backings after you've got the basic skills & understanding of how a bow works correct.
Topic: Bo Tuff - How Its Made (Read 1352 times)
