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Main Boards => The Bowyer's Bench => Topic started by: dcmeckel on December 21, 2010, 08:15:00 PM
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I know this has been discused here before,but I don't remember what the verdict was.I seem to have small bubble-like blemishes under the glass on a long-bow I just put together.Could this come from air bubbles in the smooth-on,or perhaps it's from the wood itself?It seems to be on the cocobolo and not the maple of a "Footed" limb.Anybody have any suggestions for me so this won't happen on the next one?
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pics usually needed to give you an accurate diagnosis and treatment options...
personally i'd just draw fish and make it look like it was supposed to be there...
-hov
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What kind of form did you use(air hose or rubber band), Was your glue at room temperature, did you let it sit for a few minutes after mixing to let bubbles rise before using and did you use an oven to cure? One more idea,was the cocobolo's moisture content low? Moisture may have been released while curing in oven causing bubbles.
Pictures will help.
Bummer,I know how you feel
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Also one other note... did you make sure and butter up each side of every lam making sure every spec of the lams are covered with smooth on prior to putting it together. I try to hold the lams up to a light source after I apply the smooth on to see if I missed any spots. Additionally, when I air up the form (if you are using an air hose form)...I will first shoot it with about 30 psi let it sit and squeeze out for a bit then shoot it with 45 or so, then 60 PSI.
Just a couple suggestions...Man I hate when it happens!
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Could be your form and press system or maybe not enough smooth-on. I tend to probably use way more smooth-on than is needed and I get A LOT of glue squeezing out once I inflate the air hose. It's a pain to clean up once out of the form, but so far I haven't experienced any air bubbles when finished.
How bad are they? Darker woods under clear glass tend to magnify imperfections, so if they are relatively minor, maybe there is some in the maple areas, but with the lighter colored wood you don't notice them. -Just a thought.
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I had some blemishes show up on some flat grain zebrawood once. The blemishes were only visible on the dark grains. I am under the impression that oil in the grain caused the blems when it heated in the oven. Cocobolo is a very oily wood. That, in addition to the dark nature of cocobolo will make many imperfections show up. I have been shooting that bow for 4 years and none of the blems have grown. Unless they are very bad, the bow will probably be ok. Just keep an eye on them to make sure they are not growing. Alot of bowyers have gone to strictly black glass for that very reason. Can't see the blems under black glass!!
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Thanks for all the input,nice to know I'm not alone in my misery!I use a heat box and air hose,I did not butter up each side of my lams,but then I never do,and have never had this problem.I am suspect of the very open pores in cocobolo,and on the next bow I build with this wood I am going to first coat it with super glue or something similar and see if that helps.Again,thanks for the input,and I'll let you know how the next one turns out.
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It is a good idea to heat the lams for an hour in the hot box before glue is applied it seems to let the smooth on soak into the lams. Then as has been mentioned use plenty of glue and do both sides. I also use a fiber brissle brush to clean my lams before I apply the smooth on. I have never had bubbles when using this process.
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I think coating the lams with super glue before applying smooth-on and layup is a bad idea. You really need the smooth-on to penetrate the wood. That spot, between the wood lam and glass is the weekest joint and it usually fails at the point of glue to first wood surface. More or less ripping the wood lam apart. Like loosing your fingerprints to a piece of ice. Or taste buds to a frozen flag pole. Sealing the wood before glueing would probably cause the whole belly glass to pop off in one piece sooner or later. The best in the business have this same problem with coco and bacote. Sometimes they make several limbs for one customer until they get a set that is acceptable. One of the practices used with these woods is to get the vaneer of exotic wood as thin as possible so the glue can completely permiate the lam. And as dry as possible.
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I'm with Jason on the super glue- don't use it. Just start applying glue to all mating surfaces and pressure up your form in increments to let things settle in. Darker gained woods show any problems more readily.
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What Jason said. Do not under any circumstances coat the lam with super glue. I would almost guarantee de lamination.With cocabola pre heat the lam with a heat gun. Scrub real good with a stiff bristle brusn and coat it real well with glue. I won't use bocate . The only delaminations I have seen that are because of the wood were bocate. If I did have a customer that demanded bocate I would grind it to .015 or less so that it was completely saturated with glue . I have done quite a few cocabola lammed limbs and never had a bubble by preheating and brushing. I do the heat gun on them immediately before glue up. I know a lot of guys stick the lams in the oven for an hour but Isee no reason to do that if you are using dry wood to begin with. Any air moisture will go out with the heat gun when you just warm the lams up good. Definately air up in increments. I hit it with 20, go to 40 and the 60. God bless you all and Merry Christmas , steve
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I warm up my lams in the oven tell they are warm to the touch. Along with getting rid of moisture, it may also help warm up the glue you are applying and let it settle into the wood. I like to trowel on the glue to every surface. Seems like less of a chance of air bubbles caused by brush strokes,to me. I air up the press, a little at a time also.
Warming up the lams took care of my blemish problems, so far.
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I've made many mistakes in my years of bowbuilding and here are a few you might want to avoid.
Don't put your laminations in the oven and close the door to pre heat them and then get side-tracked by something else. I came back to a box full of 36" long potato chips one time. Looked like curley fries!!!
Once I thought I would pre-heat my smooth-on because my garage was quite cold and I wanted to make it flow easier. I dished some out and stuck it in the microwave for a minute or so and got it nice and runny. Mixed it up as usual and started my glue-up. Everything went fine until I got to my last lamination and back glass. The smooth-on turned to rough-on. It started to gel with tiny boogers in it as I was rolling it on. I went ahead and finished the bow and it has held together for over 5 years, but I dont think I had much more time before I would have lost this one. Guess I got it hotter than I realized.
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I'm not sure what causes those bubbles but Ric Anderson had an preventive that I've been using since the day I read it years ago.
Glue up both sides as usual and then go over the glue with a hair drier on hot. You can see bubbles rising. Then smooth out the glue and put everything together. No more bubbles.
As Bodork suggested... I leave all the heat work, front and back of bow until last so things don't start curing out before the pressurizing.
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All of the suggestions are good. Sometimes you just get a bad strip of glass and there isn't anything you can do about it. Have heard that some bowyers will not use clear glass, other charge extra.