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  #1  
Old 02-12-2008, 08:12 AM
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Billski Billski is offline
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Default Hardshell Question

I am building a spar as a channel in a mold, using vacuum bagging. The first layup is to put the outer wrap, spar caps, and shear web cores into the mold and vacuum bag them in. The second layup is to put the shear web in on the inside of the cap and web cores. If I was just doing a plain wet layup, I would put in fillets of dry micro on the inside corners.

The process of vacuum bagging the other parts resulted in the web cores already being wetted with epoxy. Yeah, they are essentially hardshelled. I peel plied the whole thing, so the surfaces are already rough, and I will sand them prior to the shear web layup.

Not having done this particular task in vacuum bagged stuff before, I am assuming that I would do the fillets first, let them cure, and sand them before doing the shear web layups. Is this the right way to handle all of this? This is one place where I would just as soon not have to experiment to find the right way to do this.

Billski
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Old 02-12-2008, 09:51 AM
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Default Re: Hardshell Question

can a fillet be vacuumed bagged? if it can then why not do it all at once.
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Old 02-12-2008, 10:50 AM
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Default Re: Hardshell Question

The problem with vacuum bagging an uncured fillet is that micro tends to end up in the new laminations - not good. I was thinking that I could make a fillet ahead of time like we do with hardshelling to avoid that disaster.

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Old 02-12-2008, 11:42 AM
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Default Re: Hardshell Question

Well - that is the problem that i ran into in my vacuum bagging exploits.

If i make meat balls and then vacuum bag them - i no longer have meat balls, just seasoned meat in a big glob. I first put them in the freezer on a tray and mostly freeze them and then vacuum bag them. Great meat balls - you will have to come over and sample some.

So the only solution is the one you propose, filet, cure and then bag. You might want to catch the micro in the green stage, almost cured and then you get a chemical as well as physical bond
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Old 02-13-2008, 01:20 AM
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Default Re: Hardshell Question

Yum! Meat balls
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Old 02-17-2008, 10:50 PM
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Default Re: Hardshell Question

On another forum, I asked the same question, and after some back and forth, the conclusion reached was that I could do a hardshell fillet. It was also suggested that I might instead install a "rope" of roving for the fillet, either during the layup of the shear web or ahead of subsequent layups. The idea behind it is to give a more structural fillet in a place where I have a bunch of different loads interacting.

I will have a lot of glass-epoxy thickness what with it being a pretty thick layup and the fillet and then insulation from the foam in one direction and the bleeder on top - exotherm fears live here. Also, I have seen how much these thick layups move under the vacuum bag. I decided to do the fillet and the inner shear web in separate steps.

Use of a model airplane wheel as a roller was suggested for getting a good fillet with the radius that I want. Thanks to Orion for that one!

I filled the little gaps between cores and spar caps with micro-flox, then installed the fillet made from rovings, and covered it with peel ply. I did the work today and the model airplane wheel as a roller worked great. I got enough epoxy on the rovings to wet them, but only barely, and pulled them into a roughly round rope before settling them into place. After manipulating it into shape, I put the peel ply on and started working first with my fingers, then with the roller. After several passes with the roller, I got the shape I wanted, and excess epoxy started to migrate up through the peel ply. I blotted up excess epoxy twice, and the part felt firm but did not appear dry, so I stopped there. I will unveil tomorrow evening, but I have seen enough layups to know that I have a good one here.

Cheers!

Billski
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  #7  
Old 02-18-2008, 09:55 AM
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Default Re: Hardshell Question

Orion is a sharp and very helpful guy. His depth of knowledge is that of a professional, hey - he is

I have learned a lot from him, more than i can say as some of it has been telephonically
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dust

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