From: Epplin_John_A@hpmail1.90.deere.com Date: Tue, 18 Feb 97 09:01:41 -0600 Subject: COZY: Hard shell I read the applicable notes in the archives and decided to hard shell my wings. I don't intend to discuss the pros and cons of the hard shell process, it has been well covered in the past. I have some questions concerning the process. I procured West Systems 105 resin and 206 slow hardener along with what is described as "Pure Denatured Alcohol". The method I tried sort of works but seems to be lacking. I first cover the area with a micro slurry without any alcohol and remove as much as possible with a rubber squeegee. I mix one pump of resin and hardener then add microballons till the mix is too stiff to use. I then added about 5 grams of alcohol which thins the mix to about catsup consistency. I then added more micro to a stiff mix again and another 5 gr. of alcohol followed by enough micro to get a stiff shaving cream consistency. The West Mini-pumps pump about 37 to 38 gr. total of epoxy so this is 25% or so alcohol. Then the problem starts. I cannot get a smooth layer of the stuff. I tried rubber squeegee, plastic squeegee, steel drywall trowel, wooden sticks etc. A plasterer I am not. My idea was to get enough on the first coat such that after sanding to final shape there would only be minor pinholes and tears to fill. The foam cutting is what I considered to be good, the cap strip fits with only a few thousands step. No place do I need more than about 1/16 in. of fill, the average is much less than half that. Not having done this before I don't know what to expect. Maybe this is going to be more work than I anticipated. The first area that I did was the inboard foam section up to the first joint, bottom surface. After 24 hour cure, I sanded it with 36 grit paper on a 22" long 2X4 which had been planned flat. The sanding went fairly easy but I ended up with a lot of holes to fill after the first pass. Some as large as 1/2 in in diameter but only a few thousands deep. My concern is the adhesion of the next layer to these holes. Is this a normal way of doing this or am I messing up big time? Would appreciate comments from those that have "been there, done that". Thanks John Epplin Mk4 #467. From: Marc J. Zeitlin Subject: COZY: Hard shell (fwd) Date: Tue, 18 Feb 97 11:51:28 EST John Epplin wrote: >I procured West Systems 105 resin and 206 slow hardener along with >what is described as "Pure Denatured Alcohol". I really don't think you should be using the 105/206 UNDER your layups. My understanding is that it is NOT an appropriate resin for structural layups (which all hard shelling is). I used 2427 for my hard shell layups. >Then the problem starts. I cannot get a smooth layer of the stuff. I've never used 105/206 - I had similar problems with the 2427 - hence the 3 layers mentioned below. They sand easily with a 3 foot spline sander, however, so if you put it on thickly, you can get it down to shape pretty fast. >....... Not having done this before I >don't know what to expect. Maybe this is going to be more work than I >anticipated. I had to put on 3 layers of hard shell before I was happy with the shape. >..... but I ended up with a lot of holes to fill after the first >pass. Some as large as 1/2 in in diameter but only a few thousands >deep. My concern is the adhesion of the next layer to these holes. Make the next layer of micro a bit wetter, but I've never had an adhesion problem. Sand the areas with 36 grit to get some deep scratches, and it'll hold. >Is this a normal way of doing this or am I messing up big time? Would >appreciate comments from those that have "been there, done that". Sounds about right to me, except for the epoxy type - please check into whether 105/206 is reasonable to use in this context - I would recommend using your standard laminating resin, whatever that might be. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Epplin_John_A@hpmail1.90.deere.com Date: Tue, 18 Feb 97 11:19:33 -0600 Subject: COZY: Hard shell (fwd) > John Epplin wrote: > > >I procured West Systems 105 resin and 206 slow hardener along with > >what is described as "Pure Denatured Alcohol". > > I really don't think you should be using the 105/206 UNDER your layups. > My understanding is that it is NOT an appropriate resin for structural > layups (which all hard shelling is). I used 2427 for my hard shell > layups. > I appreciate your comment. One question though. What would be the weakest link in the chain? The foam or The West Systems? If there is no advantage to using West Systems here, why bother? I don't think I am going to get excited abut the small area I already used it on but will go back to Aeropoxy for the rest of the job. Thanks again John Epplin From: Marc J. Zeitlin Subject: COZY: Hard shell (fwd) Date: Tue, 18 Feb 97 12:46:25 EST John Epplin wrote: >I appreciate your comment. One question though. What would be the >weakest link in the chain? The foam or The West Systems? For the 2427, the weak link is definitely the foam. The question is how would the adhesion be (long term) between the 105/206 and the Aeropoxy. >..... will go back to Aeropoxy for the rest of the job. Sounds right. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Wed, 18 Jun 1997 22:31:53 -0400 From: Jim Hocut Subject: Re: COZY: The Sad and Premature Demise of My Canard > I think a well conducted test to the failure of this canard would >be a great benifit to setting the hard shelling question. I'm sure some >Senior engineering student would just drool over getting a project like >this in there hands. Well, it's a little too late, like I mentioned in the original post I've already done some destructive testing (and believe it or not I actually attacked the leading edge with a hammer with science in mind). I do have several sections I'm holding on to and someone can have one of those if they wish. As far as the hard shelling, I peeled back skin in a couple of places (VERY difficult), and without exception foam stayed attached (i.e. the hard shell held). The only time I saw hard shell give before foam was when I wasn't careful about roughing up the hard shell with 40 grit and cleaning it before glassing. Jim Hocut jhocut@mindspring.com