Primitive Archer
Main Discussion Area => Bows => Topic started by: upstatenybowyer on June 16, 2018, 06:47:55 pm
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I noticed this chart on the packaging my epoxy comes in, which says that the best performance for hardwood is the "medium-cure" or "15 minute" variety.
From what I thought I understood, the longer the cure, the stronger the hold. The "30 minute" cure is rated for 4500 psi, so I thought that was the best to use for splicing and wood backings.
Am I missing something? What variety do you all use?
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Some epoxies have a high psi rating but are some what brittle for flexing of bow lams or backings ,static areas its probably not a concern , smooth on Ea-40 is probably king of the hill in bow making epoxy , the stuff is amazingly strong & flexible it takes 24 hr cure at room temp , I use it for every thing now I figure why risk it with all the work that goes into a bow especially laminates ! with epoxies prep work is key with a ruff surface at least 60 grit or 36 grit and the right amount of pressure to much pressure can starve a bond.
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Great info SB. I'm new to this lam thing so every little bit of knowledge is much appreciated. ;)
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smooth on Ea-40 is probably king of the hill in bow making epoxy
I hear more about Unibond 800. What makes smooth-on better? More flexible? Stronger hold?
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Glue doesn't really have to be flexible in a bowmaking application.
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Smooth on and unibond are both made for bows, I've used both and prefer smooth on
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Unibond 800 is good glue to, but has a shorter shelf life , I had a can go bad in 8 months and smooth on has a longer open pot life , Pat ,maybe it doesent but smooth on claims there glue was design around bending applications , Im sure there are other epoxys that work smooth on is just the most popular among lam bowyers for those reasons listed , Unibond 800 is cheaper and easier to get , flooring & furniture guys use it a lot , I have been making very high stressed designs lately and the glue has been flawless for me , & its user friendly ! Smooth on can be cured quick by hot box baking I just like it based on use, but all epoxys require good even clamp pressure with no voids to achieve there full strength ! and Smooth on has a invisible glue line , I just use it like salt and pepper put it on any thing I can....lol
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Smooth on definitely has the market cornered but many general epoxies have the same or even better numbers, particularly if you are just doing a room temperature cure.
System three makes a couple with higher heat tolerance after just a room temperature cure. Gel Magic in particular is a very good epoxy with a modification that prevents it from running all over the place.
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I'm a Smooth On fan. What's not to like?
I make a glass bow once in a while. How's Unibond for clear glass? Besides adhesion, it's not exactly transparent. I don't keep Unibond around anymore because Smooth On does what it will, and more. It's quite versatile and like Stick Bender, I use it on all sorts of things. No issues, so no reason to kick it to the curb to try a different one.
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Another up side for Smooth on it makes a really good grain filler for porous woods when mixed with acid tone it dries invisible but fills the grain ! Plus if your putting on tip overlays you can keep a rag and acid tone and clean up the squeeze out before it dries for a clean no glue line joint ! Plus if your doing multiple glue ups you can use the same method ! And if it's cool in your shop you have close to 2 hour open time so no rush with the stuff.
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The west systems and resorcenal cost more than smooth on, and even though unibond costs less you get more glue ups out of smooth on so the price difference is negligible
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Mostly use titebond for my lams today but I am a fan of smooth on too: Relatively cheap, really easy to mix (I always use 50/50) really long working time, gap filling and cures perfectly at room temp without the need of a hotbox
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For me it's just accessibility. Wouldn't begin to know how to access some smooth on so it's easier just to go to any one of the several boat shops and get some other epoxy that does all the same things.
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For me it's just accessibility. Wouldn't begin to know how to access some smooth on so it's easier just to go to any one of the several boat shops and get some other epoxy that does all the same things.
I hear that, I order the smaller batch from 3rivers but if I needed a gallon I'd go straight to the manufacturer
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Lots of good info here. I just ordered some Smooth On from a sculptor's website. The had the lowest price w/shipping.
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Jeff make sure its smooth on EA-40 as the also make mold making material !
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Thanks SB. I made sure. :)
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I use uni bond 800. It's a do it all glue in all wood applications. It's cheaper than smooth on and cures fine @ 70 deg and above. It's gap filling which is nice with spliced bows and laminates in general. It doesn't have a great shelf life, but if you keep it in the refrigerator it will last a year if not longer. I've heard good things about smooth on but never tried it.
I've used weld wood resin too with good results, and that stuff is cheap (you can get it on amazon). But it did start to clump up on me in a couple months and I could only get it in the dark brown color.
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just a couple suggestions
do not thrust the cure time table.
your epoxy may be hard and workable but you will get the best performances after a significant amount of time.
It's a good idea to let your bonded pieces rest for at least a couple of days in a hot place.
Wrap it in black plastic bag and put in your car exposed to sun. 100F or more is best.
Be paranoid while mixing the two epoxy parts. that would make a great difference between a decent and an excellent bond.
Check the curing time and plan a solid mixing before use
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With smooth on you can go up to two to one for a stronger mix, I've never done it but you can weight the mix on a digital scale to get your 50/50 mix. I have gone two to one before with zero problems but it won't last as long as going 50/50
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I was referring more at the care you put while blending the components than the ratio.
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Yeah but you need the ratio right as well. I get mine all clamped to my caul and stick it in the cap of my truck, gets 125-130 easy here. I also wrap it with stretch wrap first then use my innertubes
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I also wrap it with stretch wrap first then use my innertubes
Please excuse me, but what do you mean by ‘innertubes’?
The first thing that came to my mind would mean a constant 98 degrees, but sounds rather painful... :o
(Just kidding, of course.. ..since English in not my native language, my vocabulary is very limited.)
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Bicycle tubes
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I use bicycle innertubes for stretch clamps, lots of guys do. Easy to get a consistent pressure on the bow when gluing up a lam, like a hickory backed ipe
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Ah - I see... :D
Do you just wrap the whole tubes around the limb or do you cut them open lengthwise first to get a wider strip?
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I cut the valve out and split the tube in half, lengthwise. I use it to wrap the pieces to be bonded. For a backed bow I use 1 half for each limb. I also use rubber bands for holding tip overlays after gluing. I get good, even glue lines and no dry spots that can happen with screw clamps and some other methods of clamping. I doubt you could wrap with tube bands too tightly to adversely affect the glue joint.
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If your doing the glue-up on a caul, do you just wrap the tubes around caul and the bow?
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I do the wrap first, just around the bow and then bend it into shape on the caul. There is enough slip in the epoxy to allow it to conform. You might have trouble with this if you're using TB whatever, it grabs pretty quick.
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I just cut the stem area out, I don't split the tubes, and I wrap around the caul, or at least to the caul. I wrap the bow with stretch wrap and this is two fold. It keeps everything where it is supposed to be, and keeps the epoxy off everything, the tubes the caul, any clamps you use, the seat in the truck when I hotbox it. You can also see the glue moving in the jointi wrap one limb both ways making a cross pattern then do the other limb. Make sure if you use a flat backer like a hickory strip lay a piece narrower than the bow down the center, then wrap the tubes, this keeps the backer from cupping if it gets too much edge pressure
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You can also use a simple clamp system I did this bamboo backed bow with metal 1/8 pressure strips with a sandwich of rubber strips and clamps , I hot box cure at 135 f deg for 5 hrs and unclamp in the morning all though hot boxing is not necessary it gives you a stronger bond for not much extra work according to smooth ons recommendation , there are other ways including the fire hose method ! I like the clamp method because it gives you very even pressure across the limb with no voids !
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I use c-clamps as well.
And yes, mix Smooth On, or any two part glue, really, really well, at room temperature. Some folks quit mixing too soon. You can warm it a little if it's a bit thick, but warming it too much can accelerate the cure. After clamping, I usually drop the entire press into my hot box that I made for glass bows. Its thermostat is set at 185 degrees. It cures faster and supposedly creates a stronger bond. But I've allowed it to cure at room temperature without an issue, so, who knows.
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Haven't used the Smooth on epoxy, but did order mold making studs direct from their website. Got good service and also the location of their nearest outlet(60 miles away in Denver). Very satisfied with the molds. Will get EA40 when I need epoxy
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You won't be disappointed... if you do your part.
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some hardwoods have high tangential shrinkage that may exceed the capability of a less flexible glue, so if you expect very high moisture cycling and the tangential shrinkage direction is glued to a lesser shrinkage surface that cannot move with it, say end grain, then a creepier, softer glue is recomended.
the usual care we take with our bows in regards to moisture probally negates this. I use the higher strength slower cure stuff.
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Willie, you gotta speak English man! lol Only teasing. But seriously, what is tangential shrinkage?
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Willie, you gotta speak English man! lol Only teasing. But seriously, what is tangential shrinkage?
Shrinkage across the width of a piece of wood. Wood does not usually shrink equally in all dimensions as it dries.