Vacuum Bagging

[hugh4663]

I am thinking of vacuum bagging my next board.  If I am doing multiple layers of glass on top and bottom, do I put all layers on the top and bag?  Then put all layers on the bottom and bag?  If putting all layers on at one time is the way to go, what is the best way to wet out 2 or 3 layers of 6 oz?

[aircube]

Generally bottom first then bag.  Top, then bag again.  Diff techniques for glassing, some guys lay it on dry and wet it out from the top which is a handglassing technique.  If you are bagging you can get away with putting a thin layer of resin on first and then working it in after because you will suck the excess resin away in the bag.  Either way onc ethe first layer is on the board is wet and sticky, so you have to figure out how to get the next couple of layers on straight.  I like to cut them all prior to glassing and mark them with a sharpie, then roll them up.  this way you can roll them out, wet out, roll out the next..etc.

[hugh4663]

That makes sense.  Do all the layers on one side at the same time.  I was thinking it would be rather expensive doing one layer at a time.  Lot of breather and peel-ply used.  Can you get away with re-using peel-ply?

[Dwight (DW)]

Can you get away with re-using peel-ply?

No.

You can reuse the bag, but that's about it.

[ehrawn]

Do all the layers on one side at the same time.  I was thinking it would be rather expensive doing one layer at a time.

What you are discribing is an adhesive joint between the layers: it's not only more costly in terms of time and money, it adds risk of failure. Bonding between the substrate and adhesive is due to Van der Waals forces, vice the covalent bonds (crosslinking) within the matrix. In order to get a good bond, the adhesive and substrate surfaces have to be less than 5 angstroms apart. Vacuum baging would decrease the risk of air bubble-sized voids, but 5 A is no a lot of room for error.

As a gereral rule, joints should be avoided in composites.

[pdxmike]

In order to get a good bond, the adhesive and substrate surfaces have to be less than 5 angstroms apart. Vacuum baging would decrease the risk of air bubble-sized voids, but 5 A is no a lot of room for error.

Just look at all the casting directors who tried and failed after Sean Connery retired to get a good Bond.

[pdxmike]

It also explains why the bad guys who shot at Bond couldn't kill him, no matter how much they tried.  If even 5 angstroms doesn't leave much room for error, imagine trying to aim for 007! 

[pdxmike]

Speaking of van der Waals interaction, this morning I was trying alter the force between a permanent dipole and a corresponding induced dipole in some polymers, and I got distracted by what appeared to be some alterations in the properties of the nonpolar hydrocarbon chains that were dominating and defining their solubiities.  In my distraction, I split some valence electrons off of the molecules in the polymers, and they seem to have attached themselves to my skin. 

I wasn't sure at first, but now I'm absolutely positive. 

[hugh4663]

Thanks for the responses - I agree - it was all down hill after Sean Connery!

[PauHanaTX]

I've played around with the vaccum bagging thing plenty.  I concur that it's a worthy process if you're using carbon, kevlar, wood veneers, compsands, and such.  Personnally I wouldn't go through the hassle for just putting down cloth.

Yeah, you get a little bit better glass/resin ratio, providing an improved strength maybe in the 5% range.  If you want the skinny on whether it's worthy to just vac cloth, check out Greg Lohrs post on Swaylocks.  I think your better off saving you cash and frustration and just get your hand layup down pat.  For strength, I'll put my hand layups (cloth only) accomplished with a .50 cent squeege against a spendy vac job anyday.  And I'd bet weight wise, I can come in within a pound or two on a 10' SUP.

My two cents.

[PonoBill]

Speaking of van der Waals interaction, this morning I was trying alter the force between a permanent dipole and a corresponding induced dipole in some polymers, and I got distracted by what appeared to be some alterations in the properties of the nonpolar hydrocarbon chains that were dominating and defining their solubiities.  In my distraction, I split some valence electrons off of the molecules in the polymers, and they seem to have attached themselves to my skin.  

I wasn't sure at first, but now I'm absolutely positive.  

Actually you're clearly negative. I, on the other hand was cleaning up my garage and found and old box of gadolinium-doped germanium. I sputtered it on my glide 14 over a thin layer of tin to form a p-n junction and give me positive traction.

[pdxmike]

Speaking of van der Waals interaction, this morning I was trying alter the force between a permanent dipole and a corresponding induced dipole in some polymers, and I got distracted by what appeared to be some alterations in the properties of the nonpolar hydrocarbon chains that were dominating and defining their solubiities.  In my distraction, I split some valence electrons off of the molecules in the polymers, and they seem to have attached themselves to my skin.  

I wasn't sure at first, but now I'm absolutely positive.  

Actually you're clearly negative. I, on the other hand was cleaning up my garage and found and old box of gadolinium-doped germanium. I sputtered it on my glide 14 over a thin layer of tin to form a p-n junction and give me positive traction.

Yep--I love this site.

I'm going to have to dig up some of my germaniums and try that too.

[Dwight (DW)]

A few months back, I had the opportunity to ask an expert in composites for some tips. The expert was Pat LeMehaute. http://www.lmshape.com/

He pre-wets the cloth on a table and reaches near prepreg cloth to resin ratios. That is the number one key factor in reaching super light weights.

When he vacuum bags, he doesn't need expensive peal ply or breather. He just bags for strength.

[PonoBill]

Good to hear. That's what I was going to do to my F18, but I didn't have the room and I figured if it wasn't being done, there was probably a reason. End result--the world's heaviest F18.

When I do composite work for my race cars or motorcycles I always wet the fabric on a sheet of glass and then squeegee it nearly dry before draping. I've built some very light parts that way. The biggest piece I've done that way was a carbon wing for a Radical DSR. Next time I'm gonna do it.

[hugh4663]

I read somewhere, may have been swaylocks, about making prepreg by wetting glass out on a table lined with sheet plastic. Then rolling up the plastic and wet out glass and placing it in a freezer.  This would stiffen the glass and make it easier to apply and trim. Then bag the board.  My concern with this would be the possibility of introducing moisture into the layup via condensation.  I live in northeast Florida and it is very humid here.