Today we are going to take a look at a clamp that removes such limitations and surprisingly, provides clamping force via the use of compressed air! I'd imagine there is a little physics occurring here...

The Vac-Clamp
The product is the Vac-Clamp, and the model we are looking at is the VC-4. It measures 8" x 6.3" (200mm x 160mm) and is roughly 7/8" high (22.5mm). On each corner of the Vac-clamp is a mounting assembly to screw your Vac-clamp down to a solid surface. You can either screw it down directly to your workbench, or find a larger thick piece of ply, MDF or hardwood even and mount it to that. If you use the latter option, you will need to clamp that piece of wood you are mounting the Vac-clamp onto down to your work table to keep everything stable. I mention the latter option in case you do not want to drill holes directly into your workbench. A mounting kit is available providing you with 4 heavy shank screws and a hex-head key to insert them. Alternatively, you can use panhead screws of suitable size if more appropriate to your setup needs.

Once secured down using the mounting screws, you attach the open end of the 1/8" supplied hose length to the Vac-clamp port. You simply push it in with a small amount of pressure. Once you have pushed it in as far as it will go, you verify the connection by attempting to remove the air line. If inserted correctly, you should not be able to pull it back out. This was the case in our test, so no problem there. The other end of the air line is pre-fitted with a 1/4" BSP connector (male thread). I hooked this up to my existing air supply line running from my compressor with a quickfit attachment (you may need appropriate connection fittings if your air line ends are also of the 'male' variety).

With the above completed, you are pretty much ready to go.

Air Supply
Air supply from your compressor must be in the range of 80-120 PSI to get the best clamping power on the unit. My compressor cuts out at 120 PSI and begins refilling the tank once it drops to 80 PSI, so I do not need to do anything further in the way of altering air supply pressures. The instructions warn not to exceed 120 PSI or damage to the Vac-clamp may occur. Obviously, if your supply reduces below 80 PSI, clamping effectiveness is reduced. This can actually be beneficial if you are requiring lower pressures to clamp lighter, or more fragile materials like dense or rigid foams. An on/off valve is recommended somewhere along your supply line to allow you to easily "switch" the clamp on and off. One can be ordered through the Vac-clamp manufacturer or resellers. I have an on/off valve at my compressor outlet and this worked fine. I also installed and tested the on/off valve that is sold by the Vac-clamp designers and this was equally effective. If you use the Vac-clamp regularly, purchasing their valve and installing it near your workbench (or perhaps even on one side of the bench) might be a good idea. You can use these same switch valves to control air supply to several Vac-clamps in association with two-way, or similar connectors.

It is recommended to keep your air supply as "clean" as possible. i.e. free of dust or oil. A water trap is also a good idea, however, small amounts of condensate should not adversely affect performance. I have a water trap on my compressor and on warm days, I do get a little condensation from the supply. In using the Vac-clamp, this small condensate quantity did not cause any noticeable issues.

Air consumption in use is quite reasonable - around 23-28L/min (1CFM at 80PSI). If you have a small compressor with a tank smaller than 24L, it might be fair to say that your compressor will be turning over fairly regularly if you are using the Vac-clamp for more than a minute or two. Obviously, a larger compressor with larger tank will not need to be refilled as often. 

Seal
The only other major component of the Vac-clamp is the rubber seal. This is actually what creates the vacuum when you apply your workpiece to the clamp. The seal is responsible for closing the gap between the workpiece and the clamp, and hence causing the vacuum/clamping effect. This seal can be moved around the clamp in various configurations for use with smaller workpieces that do not cover the entire surface area of the clamp, however, any configuration must include the single suction hole on the first 'square' on the unit (see photos). Naturally, the seal must be fully contained underneath your workpiece so there are no gaps for outside air to destroy the Venturi effect the clamp utilizes to draw is clamping force. Taller seals are also available to further expand the capability of the clamp. An important item to note is that the Vac-clamp will not work terribly well with porous materials. The more non-porous a material is, the better the clamp will function. Holes, cracks or other defects in the material will have a degrading effect on clamping power, as you would expect.

How it works... Venturi Effect
The Vac-clamp works by taking advantage of something called the Venturi effect. Without going into a detailed scientific analysis, the Venturi effect causes a pulling/clamping force. As compressed air hits the workpiece on the clamp, it is sucked through the small space between the clamp and the workpiece and out the exhaust port on the clamp. The sucked air pulls the workpiece down onto the clamp due to a pressure difference between the upwind (supplied) air and downwind (exhaust) air.

When supplied with high pressure compressed air with a small volume of space between clamp and workpiece, the force generated is quite large. This allows a clamping force of around 12PSI at 80PSI supply, or a holding force better than 800gm per square cm. This is around 7-8 times the holding power of a household vacuum cleaner!
Holding power is 170Kg (full face) at 1 ambient atmospheric pressure.

In Use
Thankfully, the Vac-clamp is far easier to use than it is to understand the physics behind how it works. Simply, you turn on your air supply to the clamp, apply your workpiece and away you go. It will take a second for the clamp to engage and 'grab' your material, but once that is accomplished, it's extremely difficult to remove the workpiece unless you switch off your compressed air supply. In regards to air supply and compressor tanks, I actually have a small 2HP, 24L tank compressor. I filled the tank up to 120PSI (which is cutout for this unit). I set the stopwatch and opened the valve and allowed the Vac-clamp to go to work on the workpiece. It was exactly 80 seconds before the compressor kicked in again at 80PSI, and the compressor happily refilled the tank back to 120 while continuing to supply the Vac-clamp with air. So even with a smaller compressor like mine, the Vac-clamp isn't going to run it into the ground air supply-wise. Naturally, a larger compressor with a larger tank would mean less refilling and compressor kick-in, but I was satisfied with the benefit the clamp provides over small compressor concerns.

Re-configuring the seal for smaller workpieces was a simple affair... you just need to ensure you close off the seal with a tight fit between the rubber seal ends for best clamping effect. I tried the clamp in routing, hand planing, pocket hole drilling, random orbit sanding and even belt sanding operations and the workpiece held fast. I was expecting the belt sander to send the workpiece into orbit (I took safety precautions etc) but surprisingly it battled hard and won. Admittedly, my belt sander is not the most powerful going around but it still has some kick to it! The Vac-clamp really shines in routing operations and is probably what I will use it most for in the future. The Vac-clamp does have a limitation, and this is that it becomes less effective when trying to clamp larger materials. You do really need 2 or 3 Vac-Clamps if you want to work with long boards. The reason being is that using a heavy machine on a board end far from the Vac-clamp obviously results in a force down on the board end. This acts as a fulcrum and could cause enough force to break the clamp seal on the workpiece. 

Other materials that can be clamped using the Vac-clamp include MDF, Chipboard Glass, Perspex, Aluminium, Stainless Steel and some cardboards.

I think the best property of the Vac-clamp is that it uses no moving parts. This means very little maintenance and a long expected product life. If you happen to block the air supply hole with wood dust or shavings or any other small materials, you can simply place your finger briefly over the exhaust port and the compressed air will blow out any foreign material through the top supply hole. It is certainly one of the easier tools to maintain in my shop.

Overall
I greatly underestimated the holding power of the clamp when I first saw it on the Vac-clamp website. I was very surprised at how well it holds workpieces and how simple it is to install and use. There are no issues with marking the wood as the rubber seal is not going to dig in or indent materials. Perhaps the best part of it all is the low price. You can buy the VC4 with 1 meter of air hose and a spare rubber seal for the giveaway price of US$51 ($68 Australian - includes GST). While there are no high-ticket components to justify a higher price tag, the value shines through simply because of its practicality and use it would get in almost any woodworkers shop. The Vac-clamp is a product I will use very often in my shop from now on, and for this reason alone, I award it high praise.

For more information or to order the Vac-clamp, head on over to the Vac-clamp website at http://www.vac-clamp.com

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