An experiment in vacuum bagging

A while back I was doing some imersion tests with different adhesives for laminating (primarilly Titebond III) and also wanted to figure out a way to use a vacuum pump instead of clamps. I was processing some fish for the deep freeze when it dawned on me to try something many of us already have in the kitchen cabinet for preserving wild game; behold the FoodSaver.

After running a couple tests I found out this handy little household appliance pulls over 22in. of mercury on an automotive vacuum guage, plus, the rolls of bag material can be custom sized to just about any length you'd need. Since it was raining like crazy this weekend I decided to give a try on some longer pieces of tigerwood I had leftover from my last build. The strips I ripped had some wicked checking in the grain and weren't useful for anything longer than about 3', but if it works, I may just use the blank for another low-viz hole gun.

In speaking with a gunbuilder that's already tried vac bagging with epoxy, I was told it created excessive foaming at the glue joints due to all the air being sucked out of the grain of the wood, so I decided to stick with Titebond III since the whole thing would be epoxy coated after the fact. The pictures pretty much explain the rest of the experiment, and after squaring up the first set of horizontal lams the glue joints look nice and tight. I added another lam to each side a day later, and I'll post some more pictures when the blank is squared and finished.

Quote from Dan

Is it normal for the lams to be perfectly straight to begin with, or does the suction have to pull together lams that slightly curve away from each other?

My strips were like bananas curving from side to side, but relatively flat in relation to the glue surfaces. Once I bagged and vac'd the 4 horizontal lams I clamped them between two aluminum angle pieces to line them up (perpendicular to the glue joints). If they'd been straighter side to side it probably wouldn't have been necessary. Or, if you have extra wood to play with just let the strips take on their natural curve in the bag and shave off the overlaps when you square the blank.
(in this pic the lams are stacked one on top of the other with the clamps pressing on the sides to line them up)

Pucho, I plan on epoxy coating due to the fact that Titebond III subjected to prolonged submersion will get soft at the joints. I'm not confident that oil would provide enough protection from the eliments.

Quote from Tin Man

Very cool. Is the excessive foaming with epoxy a problem only at the surface (maybe not a problem if the blank was a bit oversized), or does it affect the integrity of the whole glue joint?

I'm not sure, that's just what Phil told me when he was messing around with vacuum-bagging blanks. He ended up tossing them in the trash.

However, it may work with a few well wetted-out layers of carbon/kevlar sleeve over some type of non-pourous core material....

Quote from LunkerBuster

Jeff made a spear with his son where I think he used pvc as a core for a carbon Kevlar sleeve. This would be a great application. Wonder if he did that

That's kind of what I was implying with that statement and I'm hoping Jeff will give it a try.
I don't mess around with composite fabric, but if anyone would be willing to try it, it'd be Jeff.

The only problem I see would be the flat shape of the bag not applying 360 degrees of vacuum on a cylindrical object, say like one of Jeff's enclosed track CF hybrid barrels. Seems like there'd be a void that would fill up with resin at the 3 & 9 o'clock positions relative to the factory seams in the sides of the bag.

I wonder if he's out in the garage trying it out right now?

I squared up the blank today and it ended up roughly 1-1/2" wide by 1-7/16" high, 34" long.
I'm not at all disappointed with the results from vacuum laminating so far, and probably will finish it up by turning this experimental blank into another short Nor Cal hole gun (only a bit different than the last one).
Here's the cut-off from the butt end of the test blank (looks like pretty good glue joints to me), and also a picture of my next project, once I finish this one (Thanks for the advice Steve).....

Quote from Wood Guy

it appears that the joints on the left in the picture are a little tighter than the right.

That's a pretty keen eye you have there.
That picture was actually the off-cut from one end of the blank and the wider glue joint was a result of planer 'snipe' at the ends of the boards. I still need to trim the blank just a bit shorter on each end before I start cutting for the trigger mech and band slot.

I used Titebond III for the lamination instead of epoxy based on what I've been told about epoxy getting foamy under vacuum due to the air bubbles being quickly sucked out of the grain. I still plan to epoxy coat the entire gun once I'm finished. It's definately a lot less messy and waaaaaaaay less time consuming than traditional layup and clamping, and it seems to give fairly consistent pressure throughout the lams based on the glue squeeze-out at the joints.

So, curiosity got the best of me and I decided to try vacuum-bagging with epoxy this morning. I used some short cut-offs of the same Tigerwood (Goncalo alves) from the test blank and laminated them with some of Phil's Crystal-Clear 2-Part Resin. In the past I've used fumed silica as a thickener for laminating, but for this I only mixed parts A & B with no filler. I used the same 8" wide vacuum bags which serve no purpose for me anyway since there too small for even the smallest fish I shoot (and I shoot some small ones ;)).

Short story: no foaming, and minimal, if any air bubbles inside the bag. Not sure if it is specific to wood species since Tigerwood is so incredibly dense (s.g. of 0.90) and has such a tight grain structure (man, I love working with this wood species). Could be that other woods with more open pores in the grain may cause excessive air to be sucked through the resin under vacuum?

Still needs to be tested on larger blanks, but so far I'm thinking the $100 FoodSaver kicks ass all over the way more costly vacuum veneering methods.