Vacuum Bagging - an experiment in cheapness

[Ross Leidy]

A year or so ago, I built a greenland paddle mold according to Duane Strosaker's instructions (http://rollordrown.com/kayak/gstick.html). I made one attempt at a subsequent layup, which was less than stellar (lots of voids). I got distracted with other things and ended up setting the project aside.

Fast forward to earlier this month to the Midwest Meet at the Beach. Don Harper and Brad Shook brought a couple greenland paddles that they had made. Brad's paddle was carbon sleeve over wood, a bit different than Duane's technique, but it got me fired-up to restart my long neglected paddle project.

I've always been curious about vacuum bagging, so I thought I'd make a stab at it using my existing paddle mold. First thing: make a vacuum pump without spending too much money. I found lots of info on the web - google "fridge compressor vacuum pump" if you're interested. I found that you need to spend a little bit on a vacuum switch, gauge, and fittings if you want to regulate the vacuum. So below is the first step in my experiment. For the bag, I plan to use some sheet poly I already have, for the peel ply and breather, my wife has donated some polyester suit lining (for peel ply) and poly batting (for breather). I need to score some cheap suction cups for attaching the vacuum line to the bag - I hope to track some down this weekend.

I have guests this weekend, so my project time will be curtailed. I post more when I have something to report.

Ross

[Seppy]

Looks interesting Ross.

[Robin Boys]

Hey Ross. boy does that bring back memories.Years ago when I was building Model Aeroplanes (control line) we used to vacuum wings and used the fridge compressor as well. We just tipped 1/2 the oil out and ran them for up to 12hours. The vacuum switch was a small can with a micro switch set on top. Never worried about a gauge and we never ruined a balsa wing with to much vacuum.
Nice looking set up.
Leaks will be your biggest problem. Go for it and show us the results.
Robin

[Griffin800]

Actually two problems with a bigger settup like this. Leaks are a problem, the other is evacuating the majority of the air before you start the vacuum pump. Ideal is a small diameter wet vac and a perforated tube stuck into a corner of the bag to allow most of the air to be removed quickly. The vacuum pump will hold a vacuum well but it won't move much air.

Bill H.

[Ross Leidy]

You're right about the leaks being the main problem. The other night I did a test with poly sheeting, some breather, and duct tape to seal the edges and the tubing to the bag. Pitiful results. I certainly need to work on my technique (and possibly introduce some butyl rubber sealing tape) before I'm ready to do the real thing. With the shutoff valve closed, the pump will pull a respectable 26" Hg without the vacuum switch controlling the pump. With my duct taped experimental bag, the leaks left me peaking at 5" Hg. There's definitely room for improvement here.

I found some websites that describe using window suction cups (for hanging bird feeders) as a makeshift vacuum flange for the bag. (My earlier attempt was simply duct taping the tube through the bag.) I hope to track down some suction cups this weekend.

Ross

ps. Here's another shot of the muffler. I still need to add another pvc end cap with perforations to complete it.

[COPPERPOINT]

Ross,

Looks kinda like a mad scientist moment right outta my own garage (sometime laboratorrrry)!! My own two boys love it when I build something like that. I look forward to seeing how it plays out.

Rich

[Jimyak]

Hi Ross: great project thread!

Regarding the vacuum port, try using a metal valve stem for car rims, you will need to fashion a fender washer sized flange to
clamp the bag as the stem does not have the surface area. They screw onto a refrigeration service hose so they are real handy,
you can remove the schrader valve for more air flow if you want.

You must come up with a putty/seam tape solution to plug the leaks, folding the seams over themselves several
times really helps too. Leaks will create voids and uneven pressure for your laminates. The best use of the gauge is to check
for leaks. Pull a vacuum, shut down the pump and close the valves, then monitor the gauge, zero leak down is important. You will
never have too much vacuum.

Looking forward to observing your project.

Al the best,

Jim

[Ross Leidy]

Yeah, getting a good seal does seem to be the big challenge. On my first attempt, I used duct tape, but didn't fold the bag edges as you suggested. Before I buy some butyl tape, I'm going to try butyl roofing caulk. I know that stuff is super messy, but I have some already, so I thought I'd give it a shot.

Also, I didn't have luck with finding appropriate suction cups at Home Depot or Walmart. I decided to explore another cheap option for the vacuum port that I found here: http://www.geocities.com/reystos/vacuum/. That page appears to show a small sink drain fitting, which I couldn't find at Home Depot. I did buy a full size kitchen drain fitting to try it out. I'll post photos when I've got it assembled.

Ross

[Griffin800]

Ross,

Might try looking at Tom Yost's site and look at the folders with the inflatable sponsons, the Sonnets. He has a method of making a fitting for his home built sponsons that might work as a vacuum fitting.

Bill H.

[Ross Leidy]

I managed to sneak down to the basement for few minutes this evening to experiment with the sink-drain-vacuum-port. I spent a total of $10 for the cheapest sink drain, a threaded pvc cap, and a threaded brass pipe. If it doesn't work, the only part that's not returnable is the pvc cap, which I drilled-out to accommodate the brass pipe.

With a newly taped bag and the port installed as shown (drain flange and rubber gasket on the inside of the bag, fiber gasket and locknut on the outside), I managed to pull 15"Hg. With a hose clamp around the tubing, I peaked around 21". With the shutoff valve closed, the little pump will pull a respectable 26", so I still need to track down some leaks. This port setup is a little clumsy because of its size (scissors included to add scale), but I think it's workable.

Ross

[Crashmo]

You guys should look at these sites. They have some really simple and inexpensive parts that may solve some of your problems.

http://www.acpsales.com/home.php

http://www.cstsales.com/

Even though my pump is rated for continuous operation, I have a pinch clamp on my tube. Once the bag is pulled completely, I just clamp off the tube and let the whole thing cure overnight. I've never had a leak problem with that system.

I've been bagging foam wings for gliders for a while and they have the parts you need.

A search of radio control planes with vacuum bagging in the tag line can get you info on homemade setups. Even Youtube has been a good source for learning. I have seen standard 1 or 4 mil plastic paint dropcloth work very well with caulk, just stick the tube into the bag with caulk around the tube.

If you come up short, PM or email me at Crashmo@comcast.net and I'll throw a bunch of sites your way.

[Ross Leidy]

Oh, believe me I've been exercising google quite heavily for this project, and I've found some of the rc forums with helpful posts on vacuum bagging. Thanks for the links - I have been to them and others, so I'm well armed with sources for supplies. I'm still trying to see what's possible with non-specialized, readily available substitutes, but in the end I may need to bite the bullet and place an order. We'll see.

Ross

[stumpy]

Ross, you might also try www.veneersupplies.com for vacuum press supplies. primarily geared toward woodworking, but the equipment is the same.

[Ross Leidy]

Ross, you might also try www.veneersupplies.com for vacuum press supplies. primarily geared toward woodworking, but the equipment is the same.

Yep, that's where I bought a few of the essentials - the gauge, vacuum switch, and a few fittings. They seem to have some of the best prices.

Ross

[Ross Leidy]

I had the day off today, so I decided to go ahead and bag the first half of a greenland paddle. My test bags with duct tape on poly sheeting had mixed results. I hadn't developed a technique to get a consistently good seal, but I just got anxious to do something useful.

I made the mold quite some time ago, but I had not yet used it to build a paddle. I took the mold outside, sprayed it off, and wet sanded some rough areas with 1000 grit paper. Back inside, I applied two coats of paste wax followed by two coats of pva mold release. Mold ready to go.

I thought that the sink-drain-vacuum port was a little cumbersome, and I found I could get a good seal with rope caulk around the tubing going through the poly. I decided on the simpler of the two for my first attempt.

I found that I had enough carbon cloth to use for the outside layer with 6 layers of 6oz fiberglass for the rest. I don't know if that will be sufficient, but I'll give it a shot. I can always add another layer or two later before I join the two halves.

I used some polyester suit lining for peel ply and poly batting for breather (donated by my wife who loves to see me happily working in the shop). I sealed the poly sheeting around the layup with duct tape, and engaged the pump. It took a bit of time for it to evacuate all the air, but eventually the gauge started moving. After trying to locate leaks for an hour or so, I could not get past 10" Hg. I did detect some leaks and seemed to be able to patch, but still couldn't get to the target 21". I tried to double bag it, and that helped - but only increased the vacuum to about 13".

I'll try using the rope caulk to seal the bag on the 2nd half and see if that works any better. Right now, I'm letting the little pump run continuously for a couple hours. I should have more photos tomorrow.

Ross