It’s been years (actually more like two decades) since I last used a vacuum press during my days in a commercial shop. My recollection is that it was a cumbersome and noisy task. Are you familiar with the high-pitched whine of many vacuum pumps?
So a few months back I began investigating bag-clamping systems and became intrigued with those using a compressor and venturi* because they eliminate the need for a vacuum pump. Now, you might say, “Compressors are noisy, too!” Yes, but in using the system I found on the informative Joe Woodworker site, I learned that pairing the venturi with a switch and a tight bag means the compressor hardly cycles on and off at all.
I purchased a system called “Project V2 Plus” from Joe Woodworker’s companion web site VeneerSupplies.com ($159.50). The kit comes with almost everything you need to build the vacuum system you see pictured above; but you’ll spend another $20 or so on hardware-store items including the two capped PVC pipes and the electric switch and box. The bag is sold separately and come in a range of sizes in either polyurethane (more expensive) or vinyl. I purchased a 54″ square poly bag for $174.
OK, the costs are adding up – but when you consider the cost of the typical clamps used to come close to this size clamping capacity, the vacuum system is considerably less. And if you already have a compressor that puts out close to 5 CFM at 80lbs, you don’t need to buy the vacuum pump. I can further rationalize the cost of the system because I can use it with my lathe as a vacuum chuck, and I can inexpensively build other simple devices and use the vacuum for workholding.
Putting the kit together felt a lot like a small plumbing project, because it involved assembling the various brass fitting and parts, and making the two PVC vacuum storage chambers. It took about three hours to fully assemble the system, and it worked perfectly the first time. I was pleasantly surprised by how well the closure system for the open end of the bag worked. It’s a piece of PVC pipe slightly longer than the bag opening. You simply fold the open end of the bag over the pipe then pop on another piece of plastic (“C” shaped in section) that clamps the bag shut.
So how does it work? With my relatively small compressor, a “sidestack” model rated at 6.2 CFM at 90psi, the bag was completely evacuated in about 50 seconds. The compressor/venturi, cycled only one time as it sucked all the air from the bag. The compressor did not cycle once for the following hour as the vacuum pressure held steady at about 24″ of Hg (mercury) which translates inside the bag to more than 10 lbs of pressure per square inch.
With this new-to-me technology in the shop, I’m beginning to think about more than making my own custom veneer panels. I mentioned the uses for the lathe and workholding, but I’m also now thinking a lot more about forming curved parts using bent lamination techniques with the vacuum bag used as the clamping method.
*In the 18th century, Giovanni Battista Venturi discovered that when compressed air is forced through a restrictive nozzle, its velocity increases and the air is compressed and when it exits the nozzle, it expands and has the ability creates vacuum. From the Joe Woodworker web site.
• Learn more about veneering in Johnathan Benson’s book “Woodworker’s Guide to Veneering & Inlay” – and look for my video in late October.