Pressure
Woodworking Screw Clamps
Heavy duty woodworking clamps exert approximation 1540 pounds of pressure per clamp. Because woodworking clamps produce pressure only in one spot, to laminate a skateboard there will have to be a number of clamps used and some sort of 2 part mold that is ridged enough to spread the pressure over the entire area of the veneers. However the amount of usable pressure you will have to press a board with will never exceed 1540 pounds no matter how many clamps are used. It is possible to build skateboards using rib, Dimm and rail type presses with this amount of pressure but the chances of delamination are greater than if you used a well built hydraulic or vacuum press. That said there are plenty of great boards built using woodworking clamps.
Woodworking clamps can also be used in combination with vacuum bagging to help produce radical bends not possible with just a vacuum bag.
Atmospheric Pressure
When we press a board using atmospheric pressure we are using the earth’s atmospheric weight to push our veneer layers against a rigid surface like a foam mold. The maximum amount of air pressure, 1 atm (atmosphere) or 14.7 psi (pounds per square inch) or 29.92 HG (inches of mercury) can only be attained at sea level. The higher above sea level you are the lower amount of usable pressure you will have to press your board with. The University of Florida has a good video on the physics of this. In order to use the air’s weight to press a board we need to place sheets of veneer and mold for them to press against into a flexible bag that can be completely sealed, that the air can be evacuated from. In the aircraft industry where composites are created for strength and lightness, for wings and structural components an electric vacuum pump would be used as a standard method to evacuate the air from a bag.
Thin Air Press, how much pressure?
There are all sorts of conflicting ideas out there on the web about our TAP system. The notion of using a manual pump to produce vacuum for veneering for some is beyond comprehension. Over the years there have been many posts on forums saying that our manual system could not possibly work. I’ve seen everything from a video of someone acting out having a heart attack while using our system, to an individual posting that our kits are a toy and may work for a skateboard but could not possibly work for anything structural like what would be required in a piece of furniture. Hmmmm!
Roarockit is in Toronto, Canada which is 500 feet above sea level. At this altitude our manual system will produce around 26 HG. which is 13.08 pounds of pressure per square inch. If you are laminating longboard veneers that are 12″ wide x 48″ long the amount of overall pressure is calculated like this;
12 x 48 = 576 square inches x 13.08 psi = 7,534.08 pounds.
To put that into perspective that would be 150, fifty-pound sandbags stacked on top of your longboard.
Here is a visual of the amount of usable pressure at different altitudes with a 12 X 36″ pressing. Even though a vacuum bag can exert tremendous pressure over the entire area of a pressing in reality you only have 13 to 14 psi to bend your board into its shape. This is more than enough pressure to laminate a board with.
The higher you go in elevation the less usable vacuum you have to press your board with.
The heart of our system is a one-way valve and manual vacuum pump. The valves are designed to let air pass in only one direction. They also need to have an amount of vacuum generated in the bag before they will seal properly and start holding the vacuum pressure in. The more vacuum you generate, the harder the valves will seal.
All our valves now come with a pop-top that allows you hover a vacuum cleaner over the valve stem. (be careful not to let the vacuum suck up the top cap!!) This makes it very easy to suck the bulk of the air from your TAP bag before finishing with the manual pump. Here is a video tutorial showing how this works.
Our manual pump is borrowed from the wine industry. It produces ample vacuum to press a board with. A trick I have found to increase vacuum pressure is to sprinkle a small amount of water into the pump slide before using it on your project. If your pump eventually dries out to the point of feeling sticky. A small amount of WD40 or a silicone spray, sprayed into it works as a lubricant.
There are tutorials on the web that show a vacuum cleaner being used to build a skateboard. The amount of vacuum that can be achieve with a vacuum cleaner is only around 6 PSI. This is well below what should be used when building a board. Vacuum cleaners are also not designed to run continuously and will overheat if used improperly.
A vacuum cleaner is a low psi blower that can blow or suck a high volume of air.
Whereas a vacuum pump (including our manual pump) is a high psi pump that has low volume.
Sometimes you will see bubbles forming at the edge of your lamination while vacuum bagging. This can be a combination of two things; air being pulled out of your laminate towards the vacuum source forms bubbles and more interestingly; the water (in water-based glue) beginning to boil! If you have enough vacuum and the room is warm, the water will actually boil. Here is a video that shows the phenomena.
Ministry of Wood, Skateboard Builder Directory 
Comments
I’d like to point out that in researching the atmospheric pressure exerted on a vacuum, if, at sea level, the TAP bag will generate a maximum of 14.7 psi then at 500 ft. above sea level it is very unlikely to generate 13.08 psi. Everything that I’ve seen has led me to believe that near my elevation, under 3000 ft., I’d have about 13.2 psi. Did you use 5000 ft. as the elevation of Toronto, which is closer to 12 psi, or will the average atmospheric fluctuations be able to create such low atmospheric areas? I’m just commenting for clarification, and hopefully some valuable knowledge as to the nature of the TAP bag because I’m looking to buy one.
The picture posted in this article shows two methods of reading pressure PSI and HG. The picture of the gauges was taken in Toronto which is around 500 feet above sea level. I used our manual pump to evacuate the air from a split tube that ran directly to the electronic and mechanical gauges. The results is what I posted.
Here is a video that I recorded while doing the test.
The little manual pump we use at sea level will not generate 14.7 pounds of pressure. Unfortunately even the most expensive vacuum systems have a hard time achieving 100% vacuum.
If we could do this we would have (at 500 feet above sea level) 14.4 pounds of even pressure to press with. At 3000 feet above sea level (where you are) you would have 13.2 pounds (as you mentioned above) of pressure to work with.
If you have a electric vacuum pump check it, it will have a rating to tell you how efficient it is at sea level.(how much HG or PSI it will produce) To give you an idea most diaphragm vacuum pumps used for veneering are rated to pull around 13 psi at sea level. At 3000 feet the same vacuum pump will generate a lot less than the 13.2 psi you mentioned. Your calculation does not take the efficiency of your or my pump into consideration.
Hope this helps.
Ted
It helps alot, thank you Ted. Following up on this though, what pressures would I be able to attain with the hand pump supplied with the TAP bag?
So does this mean at 8000′ elevation it wouldnt have enough presser to press a board? i was hoping to buy a kit if i can at this elevation.