Suncure: Bubbles - Up to 2% linear shrinkage in polyester setups *PIC*

Fact(?): The linear shrinkage with a Polyester setup can be up to 2% Fact(?): A Suncure setups kicks from the surface in, A MEKP setup kicks from the inside out. I put the question marks after the ‘Fact’ because the literature (see below) seems to suggest this, and its consistent with my experience, but in the end something else might be going on, hence the question mark. I use the small Suncure UV-Tube to burn both short and longboards. The longboards are burned half a board at a time. (For example, starting with the bottom, I’ll burn the tail then the nose area, flip, lay the glass etc. and burn the tail then the nose. Four burns in all, totaling about 30 burn time.) When using this method, burning longboards half at a time, regardless of my prep, (meticulously making sure there are no dry spots and good adhesion) I would still get bubbles. But they always seemed to be in the areas that were burned second. That is, I’d burn the tail end, and bubbles would appear on the rails of the nose end, if I burned the nose, bubbles on the tail end. At first I just thought my prep was bad and made great efforts to re-prep prior to burning the second half, which made a difference, but still a bubble or two. So I went and tried to find a short, but thorough book on Composites to find out what was going on. (I figured that I had more or less eliminated me as the problem. Also, Suncure really isn’t into revealing much on the downside of their products, or shortcuts, like using the short UV-Tube to burn longboards.) My search was not complete, and there’s likely a better reference somewhere, but the book I found was cheap and answered my questions, or at least after reading it I was able to ask the right question (I think.) When curing, the prep tenses up, shrinking evenly over the surface, if you’ve used a well stirred mix of resin and kick, or when UV curing, if the UV exposure is uniform. If curing is not even then you may wind up with a little differential shrinkage. This may not be that big a problem with MEKP preps, but I think it may for UV kicked preps. Linear shrinkage refers to the shrinkage you might expect in one direction. For example, if you’ve got a 22 inch wide board, lap around the rails adding another 2 inches or so, the total shrinkage could be up to 24(.02) = .48 inches. However because it shrinks uniformly, and adheres to the deck, what usually happens is that you just wind up with a surface under tension and maybe a little (obvious) shrinkage. Which, is likely good, the surface being under tension that is. However, if one section can shrink and take the slack from another section (differential shrinkage) the section that ‘gave it up’ will wind up potentially pre-stressed, and when fully kicked, potentially lift under the tension (if adhesion isn’t perfect, or ‘drum up’, a little patch lifting in place, if there are any small irregularities.) Using the Suncure UV-Tube to burn longboards sets up a shrinkage differential on the deck through scattered light, see diagram. The deck or bottom, receiving the scattered light differentially shrinks, taking up some of the slack and pre-stressing the adjacent rail areas, (which do not receive as much scattered UV and remain virtually unkicked.) Then, when the rails in this area are finally baked, there’s no slack and they either get very tense; so tense that there is a real tendency to lift off in areas that might be irregular (small irregularities) or pull the free end more than they might do if the whole surface kicked uniformally. Add to this the fact that Suncure cures from the outside in, and you’ve got the perfect ‘bubble’ making environment. Well, at least that’s my take on what might be happening. Solution One. Get the right equipement. Nah. Solution Two. I removed two of the upper UV bulbs and biased the bake on the rails, (that is relatively more UV on the rails less on the deck, or bottom.) I also minimized the scattered light on the deck, or bottom by shielding the second half (the part not in the tube, see diagram.) Results so far. Nice, No bubbles? (… and now I’m really scared.) At the moment it seems to be working, but what I haven’t done yet, is just try either the bias method without the shield, or the shield without the bias method. Its just that yesterday, the two ideas sort of came to me at the same time, and when the prep came out so bubble free… well, now I’m afraid to experiment to try and find out if its one or the other. (I will in the end though. Apparently, I am one of the people who has just got to know, and I will likely make a mess in the process… another $15 off another otherwise nice board?.. small price to pay in the long run, I guess.) Do I suggest trying the technique? I don’t know, yet? If you’re like me, that is you’re using the wrong size UV-Tube to bake longboards, and are having bubble issues that you just can’t seem to make go away, maybe you might want to give it a try. (I’d suggest trying the shielding technique first, and if that doesn’t do it, go with the biased UV.) Reference: Aird, Forbes “Fiberglass & Composite Materials” (1996) ISBN 1-55788-239-8 This book is about fiberglass and composite construction in general. The author draws heavily on his experience from the automotive industry, however the book isn’t about automotive applications, its just that he draws many of his examples (illustrations) from that industry. Its relatively cheap ($20?), short and concise, and chuck full of insight. Is it essential reading? I’d say no, unless you’ve just got to know more about composite construction.

Good research, Kevin. Thanks for the information. You said a UV cure can shrink up to 2%. How much can an MEKP cure shrink? I use slow kick epoxy for lam. How much does it shrink? I get those unexplained bubbles in the end rails. I thought they were forming from my inexperience. Yes? (Glass unbends from tight curves. I squeegee it back down, and trap air.) Seems like heatset resins would all tend to cure from the center of the board out, kicking fastest in the center of mass. Also, like concrete, moving resin retards setup and degrades resin properties. Center board resin gets still first, and rail resin, being moved alot, degrades. Seems like Suncure would resist these forces because it kicks all at once after you move the resin around. I suspect that your isolation/concentration method, like exposing an entire side in sunlight, produces a cure that’s superior to an MEKP cure.

Good research, Kevin. Thanks for the information.>>> You said a UV cure can shrink up to 2%. How much can an MEKP cure shrink? The same amount, I believe.>>> I use slow kick epoxy for lam. How much does it shrink? I get those > unexplained bubbles in the end rails. I thought they were forming from my > inexperience. Yes? (Glass unbends from tight curves. I squeegee it back > down, and trap air.) I have never used epoxy, but my guess is that there is some shrinkage. I was able to take my bubble making down to a minimum by improving my technique, but I was still getting bubbles. As I mentioned, I’m a little scared now that I’ve had some success… You know, it worked, so now I’m bound to repeat exactly what I did for fear of making more bubbles. I would prefer to know if my differential shrinkage theory was the final culprit, and as I said I don’t really know.>>> Seems like heatset resins would all tend to cure from the center of the > board out, kicking fastest in the center of mass. Also, like concrete, > moving resin retards setup and degrades resin properties. Center board > resin gets still first, and rail resin, being moved alot, degrades. Interesting, I didn’t know this, maybe prestressing does the same, but that’s part of what you’re refering to isn’t it.>>> Seems like Suncure would resist these forces because it kicks all at once > after you move the resin around. I suspect that your > isolation/concentration method, like exposing an entire side in sunlight, > produces a cure that’s superior to an MEKP cure. But it doesn’t. Suncure kicks from the outter surface where the UV is strongest, then inward. Trust me, its a real air trap, and any air that is trap expands from the heat of the curing… it can be a real problem. Don’t get me wrong though, I am a big Suncure fan. Its fast, far less waste, and 10 times easier to work with… once you get past some downsides. Actually, after my success with the bubbles, I started to think that maybe Suncure should redesign their UV-Tube, using an electronic trigger to pre-burst the rails, followed by a complete burst. It wouldn’t be hard to make such a trigger. If I find out that I’m right I might have sum fun and make my own. Kevin

Fact(?): The linear shrinkage with a Polyester setup can be up to 2%>>> Fact(?): A Suncure setups kicks from the surface in, A MEKP setup kicks > from the inside out.>>> I put the question marks after the ‘Fact’ because the literature (see > below) seems to suggest this, and its consistent with my experience, but > in the end something else might be going on, hence the question mark.>>> I use the small Suncure UV-Tube to burn both short and longboards. The > longboards are burned half a board at a time. (For example, starting with > the bottom, I’ll burn the tail then the nose area, flip, lay the glass > etc. and burn the tail then the nose. Four burns in all, totaling about 30 > burn time.) …The only thing i use those stupid,and expensive light’s for is kicking the floor off. > When using this method, burning longboards half at a time, regardless of > my prep, (meticulously making sure there are no dry spots and good > adhesion) I would still get bubbles. But they always seemed to be in the > areas that were burned second. That is, I’d burn the tail end, and bubbles > would appear on the rails of the nose end, if I burned the nose, bubbles > on the tail end.>>> At first I just thought my prep was bad and made great efforts to re-prep > prior to burning the second half, which made a difference, but still a > bubble or two.>>> So I went and tried to find a short, but thorough book on Composites to > find out what was going on. (I figured that I had more or less eliminated > me as the problem. Also, Suncure really isn’t into revealing much on the > downside of their products, or shortcuts, like using the short UV-Tube to > burn longboards.)>>> My search was not complete, and there’s likely a better reference > somewhere, but the book I found was cheap and answered my questions, or at > least after reading it I was able to ask the right question (I think.)>>> When curing, the prep tenses up, shrinking evenly over the surface, if > you’ve used a well stirred mix of resin and kick, or when UV curing, if > the UV exposure is uniform. If curing is not even then you may wind up > with a little differential shrinkage. This may not be that big a problem > with MEKP preps, but I think it may for UV kicked preps.>>> Linear shrinkage refers to the shrinkage you might expect in one > direction. For example, if you’ve got a 22 inch wide board, lap around the > rails adding another 2 inches or so, the total shrinkage could be up to > 24(.02) = .48 inches. However because it shrinks uniformly, and adheres to > the deck, what usually happens is that you just wind up with a surface > under tension and maybe a little (obvious) shrinkage. Which, is likely > good, the surface being under tension that is.>>> However, if one section can shrink and take the slack from another section > (differential shrinkage) the section that ‘gave it up’ will wind up > potentially pre-stressed, and when fully kicked, potentially lift under > the tension (if adhesion isn’t perfect, or ‘drum up’, a little patch > lifting in place, if there are any small irregularities.)>>> Using the Suncure UV-Tube to burn longboards sets up a shrinkage > differential on the deck through scattered light, see diagram. The deck or > bottom, receiving the scattered light differentially shrinks, taking up > some of the slack and pre-stressing the adjacent rail areas, (which do not > receive as much scattered UV and remain virtually unkicked.) Then, when > the rails in this area are finally baked, there’s no slack and they either > get very tense; so tense that there is a real tendency to lift off in > areas that might be irregular (small irregularities) or pull the free end > more than they might do if the whole surface kicked uniformally. Add to > this the fact that Suncure cures from the outside in, and you’ve got the > perfect ‘bubble’ making environment. Well, at least that’s my take on what > might be happening.>>> Solution One.>>> Get the right equipement. Nah.>>> Solution Two.>>> I removed two of the upper UV bulbs and biased the bake on the rails, > (that is relatively more UV on the rails less on the deck, or bottom.) I > also minimized the scattered light on the deck, or bottom by shielding the > second half (the part not in the tube, see diagram.)>>> Results so far. Nice, No bubbles? (… and now I’m really scared.)>>> At the moment it seems to be working, but what I haven’t done yet, is just > try either the bias method without the shield, or the shield without the > bias method. Its just that yesterday, the two ideas sort of came to me at > the same time, and when the prep came out so bubble free… well, now I’m > afraid to experiment to try and find out if its one or the other. (I will > in the end though. Apparently, I am one of the people who has just got to > know, and I will likely make a mess in the process… another $15 off > another otherwise nice board?.. small price to pay in the long run, I > guess.)>>> Do I suggest trying the technique? I don’t know, yet? If you’re like me, > that is you’re using the wrong size UV-Tube to bake longboards, and are > having bubble issues that you just can’t seem to make go away, maybe you > might want to give it a try. (I’d suggest trying the shielding technique > first, and if that doesn’t do it, go with the biased UV.)>>> Reference: Aird, Forbes “Fiberglass & Composite Materials” (1996) ISBN > 1-55788-239-8 This book is about fiberglass and composite construction in > general. The author draws heavily on his experience from the automotive > industry, however the book isn’t about automotive applications, its just > that he draws many of his examples (illustrations) from that industry. Its > relatively cheap ($20?), short and concise, and chuck full of insight. Is > it essential reading? I’d say no, unless you’ve just got to know more > about composite construction.

…The only thing i use those stupid,and expensive light’s for is kicking > the floor off. How do you kick? Sunlight? Kevin