vacuum bagging

[dirtysouth]

I was just wondering about vacuum bagging. what is its purpose and how does it work. must you do this on all cold molded boats? I am just curious, I have seen this term alot and am completely ignorant to what it is. Thanks!
cole

[Andrew Craig-Bennett]

I would like to learn more about this subject.

[SMARTINSEN]

An article by Maynard Bray in WB not too long ago. My copies are out in the shop, I will look it up next time I go out.



Bray, Maynard, author and photographer: "Vacuum-Bagging EIGHT BELLS," 199:62

[kingplanker]

http://www.jamestowndistributors.com/userportal/woeimages/Epoxy/WSY-3774.jpg
The West System manual is only $5 and a good place to start when learning the Vac Bag techniques. Jamestown has the V-B supplies if you decide to pursue it further. Good luck.
http://www.jamestowndistributors.com/userportal/show_product.do?pid=3774&familyName=WEST+System+-+Vacuum+Bagging+Techniques+Manual

[Don Z.]

Not exactly about boats, but if you understand cold molding, you can see how everything here comes into play on a larger scale...

Everything you ever wanted to know about vacuum bagging but were afraid to ask (http://www.joewoodworker.com/)

[JimConlin]

The benefit of vacuum bagging is that you can apply an even pressure over a large area of irregular shape. If done right, you can get higher quality and lighter lamination.

The consumables are not expensive if you buy 'em right (Not Jamestown) . 4 mil poly film is an OK bag material and Airtech (https://www.airtechonline.com/htm/defaultnetscape.htm)is a good source for peelply, breather and bag tape.
A vacuum pump with enough capacity to be useful can be bought on Ebay for maybe $350. Look for a 1/2HP rotary vane pump.
The West System pamphlet is a good start.

[paladin]

And strip planking and cold molding veneers don't require vacuum bagging, and if one is careful a very fine and fair hull can be built with a handheld staple tool and a box knife. The advantages, depending on the size craft, are small pieces assembled by one person, and a very light weight hull compared to other techniques.

[John Meachen]

I have quite a bit of experience with vacuum bagging but none of it has been done on wooden hulls.I have major doubts about the practicality of achieving a good vacuum over a hull,I fully expect an onslaught of anecdotes from people who have done the job with what they consider to be an adequate vacuum.The reality,as Chuck states,is that a good job can be done with staples and that pulling out a few thousand staples is no fun so people try other things.
For the benefit of the original poster I will try to explain in a few sentences what goes on and why.The purpose of applying a vacuum is to enable atmospheric pressure to compact the items within the bag.As Jim states,you get uniform pressure and avoid the problem of finding somewhere to attach the back end of a mechanical clamping system and the risk of distortion that would accompany hanging several pounds of iron on the edge of the job.
The process requires the use of a proper vacuum pump,a vacuum cleaner will not perform as its motor depends on the passage of air for cooling and trying to extract air from a properly sealed bag will not yield any air.It may take minutes or hours but overheating will occur and your bag will cease to exert any pressure when it does happen.A vacuum pump should run happily for many hours.You can even obtain vacuum pumps that use a venturi principle to operate from a compressed air line.They work but make a bit of a noise and you will have a compressor running for the duration of the job.
There are two basic variations of the bagging process;you can vacuum to an impervious surface or enclose the entire assembly within an envelope bag.In either case the structure needs to be sufficiently robust to withstand the forces generated,If you are attempting to produce a flat panel you would probably choose to use something like a sheet of melamine faced chipboard as a base.With the components in place and located you need to cover exposed edges with a release film so that any adhesive that creeps will not bond to the breather cloth that has to cover the job and without which the air inside the bag can't reach the extraction point.The breather cloth should extend just beyond the periphery of the job and stop short of the mastic tape that seals the bag material to the base.The bag can be heavy polythene or something similar,the high end bagging material sold for prepreg application is not essential at ambient temperatures.With all pieces in place and the bag sealed it is nice if you have a gauge attached to the bag to prove that the vacuum is sufficient.I would want to see 17" of mercury or better,opinions may vary and more is preferred if I can achieve it.I may have skimmed over some things and if more information would be useful I would be happy to expand but it's almost midnight as I type so it will hav to be some other time.

[The Bigfella]

I described a bit of it in this thread - along with some photos, making a centreboard. The vacuum baggin discussion starts down at post 21. The pump we used is ex-TV manufacturing. It was used to pull the vacuum in picture tubes.

http://www.woodenboat.com/forum/showthread.php?t=88151&highlight=centreboard

[James McMullen]

I use a vacuum bag for laminating fancy veneers onto a plywood substrate now and again. I've even used it to bond large sections of shop prefabricated teak decking panels onto gazillion dollar giant powerboats. It's too cumbersome and expensive to mess with for everyday clamping jobs where you can get a c-clamp to work just fine though. Butyl rubber tape will stick to anything--not always only where you want it too, alas.

[Andrew Craig-Bennett]

Thank you everyone. I will stick with staples.

[paladin]

On my 44 footer.....I used plastic box banding tape and straddled it with staples....the staples were straight wire staples, not the chisel pointed ones with a thermo-setting resin on the points....after a few hours of allowing the resin to set, just pull upward on the banding tape and the staples will pull right out with the length of tape, leaving tiny holes, which will be filled with resin when fairing/sanding the hull or placing the epoxy/fabric cover on. The boat was strip planked with 7/8ths inch thick "mahogany" and two layers of cold molded 1/8th inch veneer over...when finished, there were no metal fasteners in the hull.

[SalmonMan]

On my 44 footer.....I used plastic box banding tape and straddled it with staples....the staples were straight wire staples, not the chisel pointed ones with a thermo-setting resin on the points....after a few hours of allowing the resin to set, just pull upward on the banding tape and the staples will pull right out with the length of tape, leaving tiny holes, which will be filled with resin when fairing/sanding the hull or placing the epoxy/fabric cover on. The boat was strip planked with 7/8ths inch thick "mahogany" and two layers of cold molded 1/8th inch veneer over...when finished, there were no metal fasteners in the hull.

Hey Chuck,

I'm a newbie. Where can I read/learn the method you are describing? Thanks!

[paladin]

I learned from a defunct NZ boatbuilder 30 plus years ago....send me a private e-mail with a snail mail address and I'll send you some data. I'm slow...but you'll get it this month......

[MiddleAgesMan]

To the OP--A picture might help you understand the process.

Here's a link showing the professional building of a Bolger Blackskimmer by Nexus Marine:

http://www.nexusmarine.com/skimmer_construction.html

Scroll down the series of pictures til you see the one where they have applied the first layer of plywood to the bottom. In the next picture they have the second layer in place, bagged, with a vacuum pulling all the air out of the layup. This let them build up a 1 inch thick bottom with no fasteners in the layer that will be exposed to the sea.

You wouldn't normally bag a large area like this when working with many smaller pieces but the process is the same--decide how much you can get the epoxy on, temporarily hold those parts in place, run a zig-zap perforated hose across the area, drape it with air-tight plastic sheeting, tape the perimeter, then start the vacuum pump.

There was a guy on here who built a Ken Hankinson mahogany runabout cold molded. His blog had quite a few pictures of the various stages working on a section at a time. IIRC he said his pump had a vacuum gauge and switch that turned the pump off and on during the curing phase, maintaining the proper vacuume without the need for the pump to run full time.

[paladin]

SalmonMan.....I'm sending you a copy of the Selway Fisher book on strip planking construction.....near the back is the additional chapter(s) on cold mold veneering. It is precisely the same system that I used 30 years ago...it's a very informative text. Get a small three ring binder...the binder wouldn't go in the envelope.

[Bob Perkins]

I vacuum bagged my hull - it took more time and cost more overall, but it was well worth the effort. In a cold molded hull, it makes a very tight and rigid lamination.

I also used a lot less epoxy than the staple method, and it created a hull without voids.

Like Jim said, you can use low cost materials for the bagging process.
I used poly dress liner from JoAnn Fabric (very cheap..) as peel ply.
Quit batting for breather fabric
poly sheet from Home Depot
Clay for sealing leaks

I'd do it again in a cold molding a hull..

[Oldsalt]

An article by Maynard Bray in WB not too long ago. My copies are out in the shop, I will look it up next time I go out.



Bray, Maynard, author and photographer: "Vacuum-Bagging EIGHT BELLS," 199:62

WoodenBoat School is offering two one week courses in cold-molding one of those Boothbay Harbor One-Design sloops this August.

See: http://www.thewoodenboatschool.com/boatbuilding/boothbay-harbor.php

[SalmonMan]

SalmonMan.....I'm sending you a copy of the Selway Fisher book on strip planking construction.....near the back is the additional chapter(s) on cold mold veneering. It is precisely the same system that I used 30 years ago...it's a very informative text. Get a small three ring binder...the binder wouldn't go in the envelope.

Thank you so much Chuck. I appreciate it!

[The Bigfella]

As I mentioned earlier, plenty of vacuum bagging photos in the thread I linked. Here's Barry's current project.... an art deco style chest of drawers and two bedside tables in European Beech (or is it White Beech?). All curved surfaces are vacuum bagged over the mould from multiple layers of veneer.

I'm thinking of using the mould to do one of the cabinets in Grantala's galley - so there is no sharp edge as you come down the steps into the galley.

http://i240.photobucket.com/albums/ff112/igatenby/iansecond/cab2.jpg

http://i240.photobucket.com/albums/ff112/igatenby/iansecond/cab1.jpg

http://i240.photobucket.com/albums/ff112/igatenby/iansecond/cab3.jpg

and these are two of the moulds

http://i240.photobucket.com/albums/ff112/igatenby/iansecond/cab4.jpg

[PeterSibley]

A cold moulding tip from a pro ...not me !

Staple on the veneers and leave a gap just 1/4" or so smaller than the width of your veneers .Don't spile .Use a trimmer with a 1/2" straight cutter and a guide to open the gap to the standard 3" .Staple and glue a veneer into the opening .

No spiling at all .

[andrewe]

My forefoot is hollow and several other builders have had problems getting the ply to conform in one layer. So I am using two layers with the outer one in strips, vac bagged on. This is my first use of the system (other than helping make some big bulkheads for a cat). The pump is a 1hp vane type off a milking rig.
I was recommended to use nylon dress liner as peelply, the real stuff is pricey here. From above, poly sounds good too.
The sheathing will use it too, as it leaves a fairer surface.
Andrew

[Paul Fitzgerald]

Thank you everyone. I will stick with staples.

See if you can find Arrow Ceiltile staples.
They are designed for those soft ceiling tiles, the tips splay out so the staple holds without the horizontal part digging into the wood.
Much easier to pull out with a tack puller or a flat screwdriver head.

[Jim Ledger]

Here's an example of Fiddle Back Maple paper-backed veneer applied to a fiberboard substrate using a vacuum bag.

Just roll on the glue, pop in the bag, turn on the pump, and there you go.:).

http://i104.photobucket.com/albums/m193/searover1916/P1010137-2.jpg

[Mrleft8]

Paper backed veneer? Any specific reason, or just because?

[Jim Ledger]

Paper backed veneer? Any specific reason, or just because?

Cost. Not that the material was cheap, it wasn't, but the labor was less.

It's one thing to veneer a jewelery box with sliced veneer, or even a moderately sized cabinet. However, for an entire kitchen, finding the suitable veneers and then matching and jointing them would make the job a surefire money loser, with little upside.

The paper backed veneer comes in 4 x 8 sheets, with, maybe, four or five pieces running consecutively, which simplifies matching. Even so, there were over twenty sheets involved and the pattern matching was no simple thing.

[Jim Ledger]

Here's a good picture of a vacuum bag at work. There are four pieces of 3/4" ply stacked up with glue between the outermost pieces, so, when its done, there will be two 1 1/2" thick slabs. The white board underneath is a 4 x 8 piece of Melamine, inside the bag, with grooves cut to assist the evacuation of the air. The brown piece on top of the stack is a piece of fiberboard, cut slightly larger than the workpiece, with radiused corners, to distribute pressure, and to protect the bag from puncturing on the sharp corners of the workpiece. The bag is a 4 x 8 polyurethane sack with both ends able to open and seal.

This is about as simple as it gets, but is a useful method of gluing up flat panels or gluing on laminate or veneer.


http://i104.photobucket.com/albums/m193/searover1916/Vacuumbag1.jpg