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Half bag

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Elia
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Half bag

Postby Elia » Thu Dec 02, 2004 7:11 am

Been using the sleeping bag method and have had good results but it seems to make more sense to use half bag to get the rocker and concave right. But I can't seem to get a lot of tacky tape so is they another way to seal the bag to the table? I'm thinking about using silicon but open to other ideas. Also if any one has a link of where to by tacky tape I would be interested.

zfennell
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Postby zfennell » Thu Dec 02, 2004 12:50 pm

the stuff you are looking for is sold in fiberglass supply houses like:
fiberglasssupply.com
or fiberglast.com

they call it "Sealant Tape "
but it's more like 'silly putty' on a roll.
thick, pliable and sticky.

quote from fiberglast:
"This tape will seal the bag to aluminum, steel, fiberglass, nickel, and graphite tool surfaces yet strips easily after cure. Use to plug leaks and tears in the bag that can develop during cure. Maximum service temperature is 350 degrees F. 1/2" wide, 1/8" thick, and 25' per roll."

not annonymous
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Postby not annonymous » Thu Dec 02, 2004 4:50 pm

Are you thinking about a silicone caulk? I would not do it. Silicone residue is impossible to see and almost as difficult to remove. It will interefere with epoxy bonding. Xylene is one of the few solvents that will sort of work on silicone and xylene is some really dangerous stuff.

When I first started vacuum bagging, I tried using duct tape with terrible results. Most duct tape is not really air tight at all. I recently saw a web page by a long-time Australian surfboard builder who used regular cheap masking tape to seal his bags. I haven't tried it yet but apparently it actually works.

The other problem with using tape to seal the bag is is won't work well if there are any creases/ folds in the edges of the bag. You are very likely to have some creases at the edges with a half bag on a rocker table and I'm pretty sure masking tape won't solve that problem. Sticky mastic sealant tape will.

I use the sticky mastic from fiberglasssupply.com. It is not cheap but it works the best and I made a giant zip-lock closer for my (full bag) vacuum bags so that they are reusable.

When I want to do a half bag. I made some concave rocker tables that are 3/8" thick and easily fit inside the bag, then set the whole thing on top of my regular rocker table, 'cause the thin rocker tables are somewhat flexible.

Another option is to use a router to make a thin slot all the way around the perimeter of the rocker table, then use the rubber cord made for installing window screens to seal the bag into the slot. Make sure your table material is airtight, most wood/ wood products are not but can be easily sealed w/ a couple coats of epoxy.

Trent

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Elia
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Postby Elia » Fri Dec 03, 2004 10:21 am

Thanks both of you this is the sort of information I was looking for. The router idea sounds good and may try this method. If you have a photo of the grove that you mad with the router I would appreciate it thanks
Larry

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Postby Proto » Tue Dec 28, 2004 1:10 am

Use normal mastick that they use to fix the glasses to the windows.
Make a turn around the board on the rocker table
then you only stick the plastic to the mastik.

Guest

Postby Guest » Tue Dec 28, 2004 5:18 am

mastick?? sorry, what is this stuff???

Guest

Postby Guest » Thu Jan 13, 2005 9:05 pm

I use normal masking tape - works great - super cheap - never a problem - and the bag (half bag on a Formica rocker table) can be pulled to the maximum that my vacuum pump pulls -29inHg

Kerry Baragwanath
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Postby Kerry Baragwanath » Sun Jun 19, 2005 7:58 am

Another option is to use a router to make a thin slot all the way around the perimeter of the rocker table, then use the rubber cord made for installing window screens to seal the bag into the slot. Make sure your table material is airtight, most wood/ wood products are not but can be easily sealed w/ a couple coats of epoxy.

Trent[/quote]

Hey Trent,

This sounds like an awsome idea.... But how do you cope with the bag creasing?

crabman
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Postby crabman » Mon Dec 19, 2005 7:11 pm

Butyl tape .Go to any glazing shop . Dont rout your table it wont work .To clean butyl tape off use acetone . We use butyl tape by the ton. http://www.racingfinish.co.uk


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