Vacuum and the power of nothing

Vacuum sucks!  Okay, just had to say it.  We are finally starting to use the vacuum bagging table for what it was primarily intended.  You will notice in the photo that I switched from the original plan to use a pond liner to a sheet of hard laminate for the table surface.  I tested the pond liner (not cheap) but it tended to pull up around the bottom of the parts being pressed.  I am not sure if this was distorting the parts, didn't seem to, but I didn't want to take any chances.  So off came the pond liner and on went a 4' x 8' sheet of laminate.  It was easy to apply and turned out very nice.  The laminate is also more durable than the pond liner, so less worry about gouging or stabbing the it when doing other work on the table.  And to top it all off, it cost more money, which seems to be the underlying goal in this endeavor!

Based on my experience so far, I can say that this 4' x 8' table is definitely the minimum size I would use.  All parts I need to make for the F-82 will fit on it comfortably, but I definitely would not want it any smaller.  It also works great for rolling out the fabric to cut, but since the rolls are generally either 50" or 60" wide, the table is only barely adequate for fabric prep.

In the photos you can see our auto-cycling, super-sucking, hyper-cyclonic vacuum system on the corner of the table.  I used the kit and plans from Veneer Supplies, aka Joe Woodworker (see link in column to the right).  Works great.  I made the vacuum reservoirs (pvc pipe bombs on back) about the size specified in Joe Woodworkers plans, and it seems to be about perfect.  The system cycles on and off about every 15-20 minutes when the vacuum layup is nicely sealed.  The pump cycles on when pressure rises about 4 inHg and it takes a few minutes to get back to the set point.  I am using the Gast twin piston pump available from Veneer Supplies, and it is very quiet.  Outside the boat house I can hardly hear it when running, inside it is definitely tolerable.

I also have a resin trap installed between the vacuum system and the vacuum bag, just in case I get carried away with resin application and it manages to get sucked through the vacuum hose.  I figure you only suck resin into your pump once before it needs to be replace.  Although not expensive given the performance, the pump is also not cheap (again meeting the fundamental requirement of boat construction - to spend money).  The trap would be easy enough to make, but I chose to buy this one from Fiberglass Supply.  Works well and didn't suck up yet another day of effort to fabricate.  You will notice the vacuum gauge is reading about -20 inHg, which is perfect.  This is also the best the pump could do, so good thing this was the target pressure.  Note that we are at 6500 ft elevation here in the mountains of New Mexico, so atmospheric pressure is about 12 psi, as compared to 14.7 psi at sea level.  The result is less atmosphere available above us to press down on the parts we are making.  So the pump has to work harder to get to the desired vacuum.  I am sure that at sea level, where most (slightly less crazy) boat builders probably live, the pump would do several inHg better.

At last, parts being made in vacuum.  Once everything was precut, the lay up went remarkably smooth.  It only took about 25 minutes to lay out the layer, adding resin where appropriate along the way.  From bottom to top, the lay up consists of:
1) Release wax on table top (very important assuming we don't want to permanently install the bulkheads on our table top),
2) Peel ply for a nice finished surface on bottom,
3) Bottom layer of glass fabric, in this case 12 oz bi-directional glass,
4) Foam core with custom perforations,
5) Top layer of 12 oz BD glass,
6) Top layer of peel ply,
7) Perforated release film to allow excess resin to migrate out of parts to upper layers and also allow parts to release from upper layers,
8) Bleeder fabric, which is kinda like a light fluffy blanket, used to absorb the excess resin and provide a vacuum path to the vacuum hose,
9) Vacuum film to make the upper vacuum tight surface.

You can also see the vacuum seam tape (yellow lines around the perimeter of the vacuum film) which seals the vacuum film to the table surface.  It's kinda like slightly chewed yellow bubble gum - very sticky.  To get the vacuum hose through the vacuum film you can either wrap the hose with seam tape and wrap the film around it or use a vacuum feedthrough like I did.  The feedthrough goes through a hole in the film and seals to both sides with neoprene rubber washers.  Then the hose just connects to the exposed side of the feedthrough and voila, vacuum!  I got the vacuum feedthroughs at Veneer Supply for about 8 bucks each, which was about a quarter the price of other variations I found.  They were very effective and easy to use, and are reusable until I get resin into them, but they are cheap enough that such a mishap won't break the bank.  Also the feedthroughs made the process of sealing the vacuum film very easy since I didn't have to worry about wrapping the film around the hose, which was a key location for leaks in my early tests.

If you look closely, you can see the three bulkheads being vacuum pressed under the lay up.  Works like a charm.  I'll post pictures of the finished product soon.