Introduction: Venturi Vacuum Press - Taking Wood to a New Dimension
I have been looking at expanding my hobby and getting past the seemingly blocky or overly square manufacturing in woodworking. To that end I looked into finding better ways to shape or add dimensions to my projects besides hacking away at the material. I also liked the aspect of added strength from multiple layers.
This originally started out as an experiment to see how I could implement vacuum presses into my woodworking. Because of my haste, the end product isn't as seamless or pretty, however, this experiment has lasted and worked very well, so well that I see no need to upgrade in the immediate future.
When I started my research the lowest costing true pump I could find was more than $100 (a bit pricey for me to just experiment with). I tried to make my own several ways using some pipe fittings, casting solder. They worked but I couldn't get them to generate enough suction. Maybe if I had a true milling machine or 3D printer I could have managed.
At the core of the project is the 'pump' to that end, I found that the pumps to remove AC refrigerant work just fine. I'm not advertising Harbor Freight, I just found it here: http://www.harborfreight.com/air-vacuum-pump-with-... at a price I was willing to experiment with. I hope I can show how I constructed this and some of the ways I've used it and hope that there are other suggestions for improvement.
- Air Vacuum Pump -
- Vacuum Gauge
- 2 on off ball valves
- Large Diameter PVC Pipe with end caps (3" - 6")
- Small Diameter pipe fittings ( I used copper from an old project but I imagine PVC works fine)
- PEX tubing or still refrigerator water lines
- Gator connectors
- Air compressor (separate)
- Strap Fasteners
- Base board used for mounting
- Miter Saw / hack saw
- Pipe cement (soldering material if you use copper)
Step 1: Boring Sciency Stuff
Here are numbers and principles that explain how it all works. If you're starting to tune out like Jeremy Clarkson go ahead and move to the next step where I'll start on the build.
- Here's what Wikipedia says about it: http://en.wikipedia.org/wiki/Venturi_effect (where the picture came from)
The idea of a vacuum press is to suck out all of the air from a zone, then use the pressure from the surrounding atmosphere to press in on the object. The main advantages of using this method is you can get uniform compression across any irregular surface. This is very handy if pressing or forming curves and shapes that would be difficult or impossible to otherwise form.
At sea level one a total vacuum exerts one atmosphere (ATM) 14.696 psi or a little more than one ton across a square foot. Another unit you'll see is foot pounds (32 foot pounds is 1 ATM)
It is limited in that you will only ever get 1 ATM of pressure. Here in Colorado I'm getting less than that. Also very few systems will actually get a perfect vacuum but according to my cheapo gauge I have got very close.
The Venturi Effect is when a fluid (in this case air) speeds up it creates a low pressure zone. By changing these up you can use this low pressure to create a complete vacuum to pull out all air in a container.
Step 2: Compressor Connection
There are three main components for this set up: the connection from the compressor to the vacuum, chamber and the connection to the application.
I used the compressor on off toggle to control the flow. It will connect straight to the AC Vacuum Pump then to a toggle on off valve, for the sake of instruction later we'll call this valve 1. I used brass fittings, some pex tubing or refrigerator water hose and shark bite. I didn't need any glue but a hose clamp or pipe cement wouldn't hurt. The venturi does not have any valves so you will rely on the on off switch to seal off your chamber. Good news there is no fouling if you run the compressor with the valve off.
The pump will have a lot of air flow coming out and be pretty loud, so it is a consideration during use (be aware of dust, sensitive ears and ear protection is advisable)
The pump will begin to suck air when you toggle the compressor valve open and push air through the system, you can then open your ball valve to begin sucking air out of your chamber and entire press.
Step 3: Vacuum Chamber
In the strictest sense I don't think there has to be a chamber. Having one though has been helpful for me to help keep consistency and pressure. If there is a leak in your press having a chamber provides more volume and a reserve to slow the overall pressure drop.
I like to empty the chamber as much as I can right before placing my plys in the bag. Then once everything is lined up and as soon as I seal the bag I can hit the ball valve and suck the bag down quick. This helps when extra hands are limited.
The chamber I made was made from large heavier duty diameter PVC pipes that act as the chamber, the rest is just fittings.
The vacuum is connected to the back of one chamber. The chambers connect to the vice through the Copper fittings. The small hose I used is stiffer refrigerator water line. Thinner diameter and the stiffness prevents the line from collapsing from suction. There isn't a lot of air flow through these lines so you can get away with the smaller diameter.
I constructed the Copper pipes first (I learned a while back heat and plastic doesn't work). They connect the two PVC pipes through the end caps with a pressure gauge in the middle spliced using a T joint and then exit the system. There are probably many ways to fit the chamber together, I tried to minimize the number of connections I had to make to reduce the potential for leaks and use the material I had on hand.
The caps were drilled and threaded to match the Copper fittings then I used PVC cement to seal the fittings. In total there are three caps that were tapped, 2 for the Copper pipe and exit to the project and 1 (in the back) to connect to the vacuum. I tapped into the PVC caps because they are the strongest structurally. When I was happy the end caps were threaded well I used normal pipe cement to to cap the pipes. The pipes were about 2 feet long. I screwed the pipes into the threaded taps priming the threads and caps with pipe cement first.
I took the pipes and strapped them to a board to help hold the chambers together and prevent the connections from getting bumped.
Step 4: Connecting to the Press
For the press to work, what ever application is being used need to air tight.
The easiest way to do this is by using vinyl bags. Bags are flexible so fit well with the whatever shape you choose. There are a lot of places that sell these commercially. Another option would be to find some bags and fit a connection to them. A common source may be the old restaurant soda bags used. The thicker the bag the better.
You can melt bags together with a hot iron hot glue gun tip wood burner or soldering iron. Bike repair kits can fix leaks, put patches on the outside to keep even pressure.
Step 5: Applications
Once you have your initial set up there are a lot of ways to use this.
Veneers. Veneering, like plating metal, allows you to use whatever form material you like and then glue thin strips of higher grade or designs over the surface. Traditional clamping methods can crease your veneer. If your surface it rigid all ready you can glue and apply your veneer to the surface and then place it all in the bag. you want to ensure a complete side of the bag is smooth along the flat surface. If the surface is curved you want to press over the convex bend. It can get extremely difficult to press into a cup or bowl and more often than not the bag will get snagged up on the edges or rim and provide virtually zero pressure in the center of the depression.
Forming over a mould. By using many layers of thin wood plys you can add more curves and shape and coincidentally strength than with single boards. You'll want to make a pre-shapped mould. I have cut a series of 2x4s smoothed them and screwed them together and I've built a box frame and used thin plywood or press-board. I've seen people shape concrete or other material as well. There are still many other ways, just ensure they are rigid and no trapped air (foam is a poor choice). Place the mould in the bag and glue up two plys or more at a time then line them up on top of the mould. Push out as much air as you can then toggle your chamber open to suck out the air. Once everything is the way you like it, run more air through your pump and open all your valves and watch your gauge. Continue to check your material in case it slides starts to crease or creeps under or between your mould and plys.
You can use it to inject stains or into your projects by soaking the project in your resin and then sucking the air out, the resin or stain will penetrate the wood cells and give it a very unique look. There are still a lot of other ways you can use this pump.
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