What is a vacuum bag?

WHAT IS A VACUUM BAG?

The vacuum bag is made up of two parts—the bag and the pump. The bags are made from either polyurethane or vinyl. There are multiple reasons why we prefer polyurethane bags. First, they are clear—you can see right through them. This is great for lining up pieces as you are working. Second, the puncture resistance of polyurethane is much higher than a vinyl bag. And it has greater flexibility. Polyurethane bags will return to their flat shape much faster than a vinyl bag. You can simply roll the bag up into a compact tube and store it away when not in use. Because we use the vacuum bag quite often in the shop, we designed a custom table for our bag so we can leave it out if we want to. We also built a compartment in the table to store the bag. 

You can get a vacuum bag in almost any size; we use a 5’ x 10’ bag. You can also order custom sizes. We went with a 5’ x 10’ bag to allow for a full-sheet panel. Of note, you can put more than one sheet at a time in the bag. But keep in mind, as you add pieces and it builds up, it will take away from the overall length and width of the bag size.  

AIRTIGHT ZIPPER

Some vacuum bags use a roll and clamp approach. We chose a bag that uses airtight zippers designed for industrial use. The advantage to the zippered bag is that they are easy to use and have an airtight seal.  

KEEP IT FLAT

The most important rule to remember when using a vacuum bag: You’ve got to keep the surface level and really flat. Whatever you’re clamping, if you want it to be flat, the subsurface has to be dead flat. That is why we built a custom table just for this vacuum bag. The table is perfectly flat and level in all directions. Then we designed a platen that goes inside of the bag. We cut kerfs (a shallow cut or slit the width of a saw blade) in the platen, which allows the pump to pull the air from the entire bag. Otherwise, the bag would basically stick to itself, allowing air pockets throughout the bag. And you don’t want that. The goal is to have an even pressure surface clamping over the entire item. 

HOW IT IS USED

Once the platen is placed in the bag, put your material on top of that. Zip the bag. Turn the pump on, and the air will suck out of it through two holes in the platen that the pump hoses feed through. The pump has multiple pressure settings for various uses. By adjusting the pump pressure, Ken was even able to use the vacuum bag on glass. Applying mastic to the glass with a spreader like a thin set application, the result was the glass was flat and tight to the substrate, ensuring no “fun house” distortion. Another cool project was veneering some steel for a magnetic jewelry board. 

However, most commonly, we use the vacuum bag for veneering to create our own plywood or MDF. We’ll take some very thin wood—paper-thin—and use it to veneer to both sides. We do quite a bit of veneering of flat stock in the shop, but the real reason we bought this nifty piece of machinery is for doing curved work.  

Curved cabinetry looks amazing; it creates an inviting feeling to any space. No harsh edges, just soft curved appeal. We used the vacuum bag when building the curved cabinets for a kitchen renovation in Boston. In fact, I said we wouldn’t start the project until we bought a bag. It was that crucial for our curved cabinetry work. 

Although we made the solid stock in a form outside of the bag, the center panel absolutely had to be dead flat. And this where the vacuum bag comes into play. The pressure going across the whole surface is what gives us the perfect degree of flatness. We can create a form that provides us with the radius we’re looking for. And then we were able to basically make our own plywood using thin strips of plywood or thin sheets of wood and curving and shaping it as needed. 

Another important step is using guide blocks within the bag. You certainly don’t want items to shift in the bag and add an unwelcome twist. That will cause huge problems later on during installation. So, the guide blocks are used to keep the pieces from slipping or moving around.  

FINAL THOUGHTS…

Now you’ve got a glimpse into another aspect of the NS Builders millwork shop and how the right tool can make all the difference. And a huge thanks to Ken for helping me to address the technical stuff! 

If you’re feeling a bit envious of those curved custom cabinets, contact us to find out how we can get started on your high-end kitchen renovation. Let’s start this project together!

—Nick Schiffer