Vacuum Bagging Extra-Long Assemblies
Vacuum veneering of very long pieces is complicated, but doable. October 11, 2007
We have a project coming up that requires an 11' cheery veneer countertop with solid front lip. I can't find a press long enough to do this up in one piece. What's the best approach to fabricating this piece? My finisher says I should press two sections, then join them with under-counter connectors, apply front edge, and take it to him for finishing. I'm a bit worried that the finish will crack at the joint when we try to move it to site, scribe to walls, etc.
From contributor A:
In the boatbuilding industry, it is common not to use the typical vacuum bag that woodworkers commonly use. Instead you take an airproof substrate (melamine) and build a temporary table out of it. Then you purchase bag film, mastic tape, and breather medium. You cut the bag substantially larger than the table (at least 12" on all sides). The film comes in 60" widths and rolls of length. You can use the mastic tape ("suck" tape) to seam bigger bags if necessary. Leave a 3" border on the melamine and wax the interior so your part will not bond to the melamine. Place the mastic about an inch inboard on the perimeter. Stick your vac hose in the mastic and throw a couple of pieces over it so it doesn't leak.
Throw your part on the table, add the glue, place the breather medium (filter fabric), throw the bag film over the top, and start to remove the mastic cover and work your way around the table. In places you will have to make hems to take up the extra film. The corners need large hems to prevent bridging across the part.
West System offers a 20 page pamphlet describing this with pictures. We vacuum bag 100 ft fibreglass boats using this method. LBI is a good source for any vacuum bagging supplies, or Jamestown distributors. The West System techs are also very helpful.
From contributor V:
If you have access to a hot press, do your pressing in 2 stages. Press the maximum length that will fit, then slide the piece so you can press the remaining. The only problems you may run into are if the platens on the press have a slight lip. They may cause a dent across the grain, which can be difficult to sand out.
From contributor T:
It sounds like you have a little time, so I would order the material already laid up by someone that has that pressing capability.
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