Vacuum Bag Clip Seals
I’ve found that when vacuum bagging parts, it’s always FAR easier to put the mold in a tube, instead of bagging it with a flat sheet. When you bag with a flat sheet, often times if your mold has compound curvature you need to put pleats and “rabbit ears” in your bag, so that it will conform to the entire mold. This is often very time consuming, and problematic in terms of getting a perfect seal. In addition, at $8-$10 per roll of sealant, the cost of the tape alone can add up quickly, especially when doing parts that require multiple steps, like the classic 2-core-2 style construction often found in aircraft skins. About a year ago I started to put everything in a bagging tube instead, and use reusable bag clips like these sold by CST to seal the ends of the bag (scroll to the bottom of the page). The largest one they sell is 38″ long, which is meant for a 36″ tube. Since I often use this 48″ 4 mil Poly Tubing sold by Uline as a bagging tube, I needed to find longer clips to seal the bag, or else I would have to go back to using tape. My friend Dana pointed out that the clear plastic u-channel is simply some sort of protective edging sold by glass supply houses. A trip to my local glass supply house confirmed this, and I was able to order 8 72″ pieces for around $35. They had it listed as a 1/4″ plastic trim, and the part number is 2-D720. This of course may mean nothing to your local supplier, but it’s at least a start. It comes in lengths up to 12′, but I had them cut them in half since I didn’t need them that long, and the shipping costs would have been far more at that length. The next thing to find was the rods. This one was easy – McMaster-Carr is just about my favorite vendor of all time. You can call them up and have conversations that start like “hey I’m looking for this thing-ey…it’s like….made of plastic and stuff” and more often than not, they will find what it is you’re looking for. Here in California they ship with a company called OnTrac that offers overnight shipping for cheap. I’ve placed orders at 7 pm and had it show up the next morning at 9:30 for $5. Really. Anyway, so McMaster-Carr has fiberglass reinforced rods that come in 5′ and 10′ lengths for very cheap. You can get the 3/16″ and 1/4″ rods I use here – scroll down the page to the section called Rods – Smooth Finish. Why the two different sizes? Well, I found with the 4 mil poly tubing I use, the 1/4″ rods were just too tight of a fit into the plastic channel. When I use thinner bagging material, they work better, but I’ve found it’s best to keep both on hand for the best fit. Of course a big factor in this is just what kind of plastic channel you find – it may or may not be the same as what I got, and I can assure you the fit will be slightly different. The last piece of the puzzle is to get your vacuum lines into your tube quickly and easily. I’ve found that the aluminum valves made my Airtech found near the bottom of this page here work very well. Scroll down until you find 401C Twist Lock Aluminum Vacuum Cup Assembly. With bag tube, these bag clips and that Airtech valve, you can bag your parts without the use of any sealant or bagging tape. It also takes just a minute or two to get your part under full vacuum, which can be very helpful with large or complicated layups where you might be bumping up against your resin working time. The only disposable cost per part is the tube, which I find with the 4 mil I can get several uses out of. The tubing comes out to around $1.25 per yard, so the amount of money wasted on consumables is quite low.