Understand the 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.

In order to use the air’s weight to press a board we 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!

Click to see a short video on how much pressure can be achieved with the wine pump and valve

Click to see a short video on how much pressure can be achieved with the wine pump and valve

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, it would equal 150 x 50 lb. 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.

To see an actual pressure test from sea level to the top the Haleakala Crater on Maui Hawaii, click on the picture..

HIGH-Pressure-LOW-Volume vs LOW-Pressure-HIGH-Volume Pumps

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.

A vacuum cleaner is a LOW psi blower that can blow or suck a HIGH volume of air.

Whereas an electric vacuum pump and our manual pump, are HIGH psi pumps and LOW volume.

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 high psi 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.

How much pressure is needed to press a skateboard?

This chart explains how much pressure you need for vacuum veneering (see red bar), and how much vacuum each source will provide.

Water Boils in a Vacuum

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 this happening.