At 06:14 PM 7/31/2002 -0700, Jeb Bushell wrote: >Another great post. Many thanks, but may I look the >gift horse in the mouth?
Of course, be aware that this horse might bite. >I have built several carbon/balsa spars and have yet >to find the perfect glue and procedure to join >end-grain 4lb balsa to pre-cured carbon strip. I was sorta planning on doing a wing with that construction method, too. I've never actually done a glue joint with these problems. Most interesting. >Laminating epoxy (MGS) soaks into the balsa too much >and the subsequent peel strength is too low to be >really good in my amateur opinion (but it's still the >method of most used). Are you saying that the adhesive you put on moves away from the joint area and starves the interface area? If that is the case the solution seems simple (easy to say for someone who's never actually done it.). Put a sealing coating or a priming layer of not-too-much MGS on the balsa first. Let it cure out. Then assemble the spar with a second treatment of the MGS epoxy. You only have to be as strong as 4 lb balsa in shear. > Thick epoxy (PC-7) does not stick to the carbon very well How are you cleaning the carbon? It really should stick as epoxy does stick well to epoxy. Use the same method I suggested for cleaning aluminum, although you won't have to scrub for as long. You aren't touching those surfaces with your grubby fingers or mixing in extra hardener to speed it up are you. (Sheeeish, can you imagine anyone doing that! Must be an EE major.) > and is hard to apply thinly, which is essential. I presume you mean for weight reasons? Any squeeze-out can be wiped off. > The polyurethane stuff >aka "gorilla snot" is no good for all sorts of reasons >- see Tony Estep's recent post. My best results have >been with thick CA but the fumes from about 0.5 oz of >CA nearly did me an injury. Alternately use a little CA, thick or thin -- experiment -- on the balsa to prime it (outside with ventilation) and after the CA is cured out (don't use kicker as I have no idea what it will do to the epoxy) then use epoxy to complete the assembly with the MGS. Anything to cut down on the mobility of the MGS into the balsa should work OK >So I'm thinking Goop. And clamping, not bagging. I can't help but think you want a rigid adhesive here, or at least something more rigid than GOOP. >Do you have any suggestions? A single malt, Islay scotch whiskey at least 24 years old and you won't worry about this silly spar for days. Cheers, Bill -- In other words, apart from the known and the unknown, what else is there? Harold Pinter Bill Johns Pullman, WA RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
