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How To Build A Pressure Vessel For Dying Your Own Veneers

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A few of the guys on this board have vacuum pumps. They're really handy tools. One variety hooks up to an air compressor and pulls a vacuum via a venturi. The other variety is a stand alone unit powered by an electric motor. Vacuum pumps can be used for a number of guitar related tasks. Some include vacuum powered work holders, vacuum attached routing templates, acoustic soundboard/back brace gluing fixtures, veneering, vacuum assisted wax potting(of pickups), and the list goes on.

This tutorial will show you how to make a pressure vessel out of materials that can be found at virtually all hardware stores and at a reasonable price. This tank is meant to be used for dying your own veneers. Drawing a vacuum on the tank while dying the veneer removes(most of) the air from the veneer. This forces solution carrying the dye into the fibers of the wood. Another method, not covered in this tutorial, for dying veneers is pressure cooking. In this process, veneers are placed in a pressure vessel that is heated and in turn raises the pressure inside the vessel, thereby forcing the dye into the wood. That said, DO NOT, under any circumstances, try to heat the vessel described in this tutorial in an effort to dye the wood by the latter method mentioned. Heating the vessel described in this tutorial could possibly cause catastrophic failure of the vessel, sending steaming hot liquid and melted plastic flying upon failure.

This vessel consists of several main sections: an outer pvc tube, an inner pvc tube(this is included simply to reduce the amount of solvent needed in the dying process), and solvent level sight tube.

Bill of Materials:


-(1) approx. 3' of schedule 40 4"dia PVC (avoid schedule 20, it will likely collapse when you apply a vacuum)

-(1) approx. 3' of schedule 40 3" dia PVC (again, avoid schedule 20)

-(1) 4" to 3" PVC reducer

-(2) 3" PVC Test Cap(s)

-(1) 4" PVC Male to Male Coupling

-(1) 4" PVC Cleanout fitting with Plug

-(2) 1/8" ID Barb x 1/4" MIP fitting(s)

-(2) 1/4" FIP x 1/4" MIP elbow(s)

-(1) approx 3' of 1/4" OD clear(it's actually only semi-transparent) polyethylene tubing(Avoid any other type of tubing as it may collapse under vacuum or dissolve when exposed to solvents)

-(1) small can of PVC cleaner

-(1) small can of PVC cement

-(1) male vacuum fitting(the one used in this tutorial is available at veneersupplies.com)

-(1) roll thread sealing tape.


-Hand drill or drill press and drill bits

-something to cut the pvc with, hacksaw, bandsaw, angle grinder w/ cutoff wheel etc.(avoid circular saws w/ woodcutting blades, they tend to make pvc tubes explode :D )

-dremel with sanding drum or spindle sander or half round rasp, etc.

-1/4" NPT Tap

-Rubber Mallet or similar


1. First cut your two pieces of pvc to length. My pressure vessel is about 36" long, overall. You may want to make yours shorter or longer depending on the size of veneer you plan to dye. Remember that you can coil up the veneers inside the tube, so narrow, long veneers don't require long pressure vessels. Make the 3" pipe about 2.5" longer than the 4" pipe. Make sure that the ends of the tubes are smooth and even, sand if necessary. This is particularly important for the 3" tube due to the nature of the test caps that will be fit to it later.

2. Next, measure about 2" away from each end of the 4" tube and mark the tube in each place. The 2" is to accommodate the fittings that will go on either end of the 4" tube. Make sure both marks fall on a line parallel to the direction of the pipe. Drill a 27/64" diameter hole and tap it using your 1/4" NPT Tap. Only use about 1/2 the length of the tap as over tapping the hole will yield a loose fit.

3. Wrap the male threaded portion of each of the 4 brass fittings with thread sealing tape as shown in the photo below. With the threaded portion facing you, wrap clockwise around the thread to avoid unraveling the tape when the pieces are screwed together.


4. Screw each 1/8" ID Barb x 1/4" MIP fitting into a 1/4" FIP x 1/4" MIP elbow.

5. Screw the each barb/elbow assembly into the holes that were drilled and tapped in step 2 as seen in the picture below. When installed, the two barb fittings should be pointing at one another. You may find that the male end of the elbow sticks out about 1/4" on the inside of the 4" pipe. To remedy this, I sanded down the excess, after installed, with a dremel and sanding drum. However, you may wish to use a bench grinder or sander to remove the excess before installing. Leaving the extra threads protruding will make it difficult to put veneers into the vessel, once assembled.


6. Cut your polyethylene tubing to length. It should be able to be fitted onto both barb fittings while as straight as possible as shown in the picture below. This tube will serve as a solvent sight tube. It will show you how high your solvent is inside your vessel.


7. Next, you will have to remove the lip inside of the 4" to 3" PVC reducer. I did this with a dremel and a sanding drum. However, you may do it however you see fit. Be careful not to sand the inside of the 3" portion of the reducer. This may prevent you from getting a good seal between the pipe and the fitting. Before and after pictures can be seen below.


8. Clean the inside of the 4" side of the reducer and and one end of the 4" pipe(about 2" is sufficient).

9. Once the cleaning solution has dried, apply PVC cement to the two cleaned surfaces and fit the reducer to the 4" diameter PVC tubing, as show below. If you find it difficult to get the two pieces to mate, use a rubber mallet to force them together.


Edited by thegarehanman
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10. Next, clean the inside and outer lip of one end of the 3" diameter PVC pipe(about 1/2" is sufficient). Also clean the surfaces of one of the test caps that will mate to the 3" PVC pipe.

11. Once the cleaning solution has dried, apply PVC cement to the cleaned surfaces and mate the test cap to the pipe.

12. Clean the inside of the 3" end of the reducer and the outside of the 3" pipe on the end that has the test cap glued on. Also clean off any numbers, writing etc. that's printed on the full length of the 3" pipe. Skipping this step will likely result in your first few batches of veneer having a tinge of the color of the ink used on the 3" pipe.

13. Once the cleaning solution has dried, apply PVC cement to the cleaned surfaces. Slide the 3" pipe section into the 4" section, test cap end first, and mate the two areas that just had cement applied. You'll likely need a rubber mallet to get these to fit together well. Pound the 3" section into the reducer until the 3"pipe is just about to come out of the other end of the reducer, as shown in the picture below.


14. Clean the outside of the remaining end of the 4" pipe and the inside of one side of the 4" coupling.

15. Once the cleaning solution has dried, apply glue to the cleaned surfaces and mate the coupling to the 4" pipe as shown below.


16. Clean the inside of the remaining end of the coupling and the outside of the cleanout fitting.

17. Once the cleaning solution has dried, apply glue to the cleaned surfaces and mate the cleanout fitting to the coupling.

18. Drill a few small(1/8" is fine) holes in the remaining test cap and cap the exposed end of the 3" pipe as shown in the picture below. This will prevent solvent from getting into the 3" pipe when you fill the vessel with solvent and dye. You do not need to glue this test cap in place. These holes will also insure that the pressure on the inside and outside of the 3" tube is equal, which translates into fewer areas on the vessel that have to deal with a pressure differential. The other advantage of this is that the suction of the vacuum is placed on the other, non-drilled, test cap, effectively sucking it against the 3" pipe, making the seal that much better.


19. (Note: this step only applies if you're using the veneersupplies.com male vacuum fitting) Now, drill a 7/8" hole in the direct center of the cleanout plug. To get the inner washer to fit into the cleanout plug, you'll need to grind a bit off of the perimeter as seen in the first picture below. Install the male vacuum fitting as shown in the second picture below.

th_000_0258.jpg th_000_0257.jpg

20. Wrap the threads on the cleanout plug with thread sealant tape. I found that the cleanout plug alone did not create a good enough seal to hold a vacuum. A few wraps of tape is enough to get a nearly perfect seal on the threads. I let the vessel sit with a vacuum on it for about half an hour and my vacuum pump did not need to cycle even once.

21. Finally, make yourself a small metal rod to aid in removing the veneers from the vessel, as the gap between the 3" and 4" pipe is pretty darn small. I simply used a coat hanger that I straightened out. I bent one end of the coat hanger to fit between the two pipes as shown in the two pictures below.


You now have a pressure vessel that's perfectly suited to dying veneers while using the minimum amount of solvent necessary. Yay you!


FINAL NOTE: This pressure vessel is designed to be operated upright, as shown in the picture below. Operating the vessel on its side may result in liquid being sucked into your vacuum pump, thus destroying the pump. When operating the vessel, make certain that the vessel can not tip over or use a catch basin between the vessel and the pump to catch any fluid before it can get to the vacuum pump.


I'll post some more pictures and tips once I get a chance to dye some veneer.



Edited by thegarehanman
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You probably will, and I have an odd feeling that you already did. That stuff is made from pulp, right? If so, it should absorb the dye pretty evenly. I just wouldn't use water, if I were you. I bought an 8 gallon drum of lacquer thinner so that I'd have enough to do a few test runs. I don't want to use water and risk warping the veneers. If nothing else, using a vacuum to dye veneers(all the way through, mind you) will yield more uniform, not to mention faster, results. I'll get back to you in a few days once I do some test runs.



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Note that the veneer looks lighter in the center only because of the flash from the camera. The color is actually very uniform throughout the whole piece.

Ok, I did a test run. I figured out that about 3 cups of solvent will give you about a foot of fluid height. Also, the barbed fittings don't make a perfect seal with the tube, but a little caulk around the end of the tube on the barb fitting does the trick. The pictures above are of flamed maple. I used 3 cups of lacquer thinner, mixed with 10 parts Stewmac Cherry red, 10 parts Stewmac Vintage Amber, and 1 part Stewmac Black analine dyes. After I figured out the combination of dyes, it took about 5 minutes to mix up the dye, put in the veneer, and then pull a vacuum. The best part is that I could have just dyed 10 times that much veneer and it would have taken the exact same amount of time. Once out of the lacquer thinner and dye, the veneers are dry in another 5 to 10 minutes. Something to remember is that you can save the mixtures of dye in mason jars or something else solvent proof, should you want to use the same color again.



Edited by thegarehanman
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Chris, I guess you haven't seen the bubbles that veneer gets when exposed to water. The veneer is not warped, it simply must be curved to fit into the tube. Actually, when you purchase large sections of veneers, it often comes in tightly coiled rolls, just like that. Bends aren't a problem, it's bubbles that you have to worry about.

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