Tuesday, July 17, 2012

Veneer - glue up and vacuum pressing process

I prepared the veneer skin by seaming the veneer with veneer tape. The side you see with the tape is the show side and the other side is the glue side. This particular glue up is destined to be the balancing veneer on the floor of my entertainment center. In other words, it will be on the bottom of the cabinet facing the floor, so all pressure is off to get this perfect!
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Cauls are prepared for both sides of the veneer. I use 3/4 inch MDF that I’ve pre covered with plastic to ensure that I don’t glue the panel to the caul.
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I’ll spread the glue with a paint roller. I’ve found these black rollers work very well.
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Gloves and blue tape need to be on hand.L1030373-2012-07-15-19-46.JPG

The glue is a two part glue consisting of a resin and a hardener mixed in a ratio of 4:1.L1030376-2012-07-15-19-46.JPG

I mix is slowly adding a little of the powdered hardener at a time, then stirring until it has been incorporated into the resin.
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Here is the glue mixed and ready to spread. It has the consistency of thick syrup.L1030378-2012-07-15-19-46.JPG

I pour some on the MDF panel that is the substrate for the veneer skin I’m applying.
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The paint roller is used to spread a thin coat of the glue evenly on the substrate.
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I carefully lay the veneer skin on the substrate with the glue face facing the glue. This may seem inherently obvious, but it is very easy to make a fatal mistake at this point (which I know from experience!)

I use clear packing tape in a few places around the substrate to fix the veneer skin to the substrate so it will not move as the vacuum press starts to apply pressure.
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I place the top caul over the panel and very carefully align it so the substrate is completely covered. I size the cauls so I end up with about a 1/4 inch overhang.
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I use blue tape to bind the sandwich together. The idea is to tape the entire assembly so it will not move as the vacuum press begins to apply pressure.
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The assembly is very heavy, so I’ve devised a very simple system so I can do this by myself. I’ve built the veneer sandwich on a movable cart that is slightly higher than my vacuum press. I can position the assembly in front of the press and carefully load it into the bag.
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I seal the bag and turn on the vacuum.L1030389-2012-07-17-08-46.JPG

Once the vacuum has removed all the air inside the bag, the pressing is underway with about 1400 pounds per square foot of pressure on the sandwich.
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After the glue has cured (how long this takes depends upon the temperature, but it takes a minimum of four hours) I remove the panel from the press. Now I must remove the veneer tape. I do this using a sponge to soak the veneer tape with water to reactivate the glue. Then it is a simple matter of carefully easing the tape off the panel.
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Monday, July 9, 2012

Veneer - specialized tools and simple joinery techniques

Working with veneer does require a few specialized tools.
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Cutting veneer can be done using a variety of tools depending upon the type of veneer and the specific type of cut being made. A good straightedge and a veneer saw is one of the more common methods.

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The fabric cutter (white with orange) is an example of a tool designed for another purpose (cutting fabric) that can be extremely useful for certain types of veneer cuts. In addition to the veneer saw and fabric saw, I occasionally us a very, very sharp chisel that I’ve slightly modified to cut veneer, and I also have a surgeon’s scalpel that is “scary” sharp. I tend to use the scalpel more when I’m doing marquetry or when I’m trying to cut difficult veneer with squirely grain.

The soft bristle brass brush is used to massage the moist veneer tape to get the best possible surface contact with the veneer tape. The little roller is a wallpaper roller I stole from my wife years ago. I use it to massage the seams to get the seam perfectly flat.

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Veneer tape is probably the most unusual item. It is a thin paper tape with a moisture activated glue on one side. This tape dispenser makes moistening and cutting the tape easy.

The following sequence of photos shows the process of seaming two pieces of veneer together. I first cut both pieces for the joint using a straightedge and veneer saw. Next I use blue painters tape to carefully align the two edges together. I use one inch veneer tape across the joint followed by two inch veneer tape along the joint. The bottom photo shows the result after pressing. The photo will not really show it, but the resulting joint is virtually invisible!

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Two pieces of veneer edge jointed and ready to be joined.

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Blue tape is used to bring the edges into precise contact.

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Veneer tape is placed across the joint.

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Blue tape removed.

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Veneer tape placed along joint on top of joint.

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Result after pressing. The idea is to make the joint disappear.

Friday, July 6, 2012

Veneer - Substrate and glue

I’ve heard a lot of misinformation about gluing veneer, particularly regarding the type of glue you should be using. The absolute worst glue you can use on a veneer project is contact cement. I’m amazed at how often I see some magazine advise using contact cement for veneer, or worse yet, occasionally on a woodworking television show. Contact cement is formulated to be used with rigid material like formica. Contact cement does not form a rigid glue line and always maintains a certain amount of flex or give to it. White and yellow glues are better, but still do not result in a rigid glue line. Additionally, the working time for white or yellow glues is relatively short and you have to work quickly before the glue sets up. The best glue for working with veneer is one of a family of glues based on urea formaldehyde because it has a relatively long open time and cures based on a catalytic reaction.

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I’ve used a product called Unibond800 for years and have great success with it. Unibond800 has the unique characteristic of an absolutely rigid glue line after curing. This makes this glue ideal not only for veneer but also for bentwood lamination work. When using it for bentwood lamination, I experience virtually no spring back after removing the work piece from the glue form.

It does have a couple of drawbacks. First, it has a relatively short shelf life of about 6 months to a year, depending upon the temperature you’re storing it at. And second, since you add a catalyst powder to the glue, you must use whatever you mix because whatever is left will cure rock hard. Third, and this is a relatively minor one, the glue cures best in a warmer environment. If you are doing a glue up and the temperature is below 70 degrees, you need to cover the project with a heating blanket, or else the glue might not set at all.

The substrate you choose needs to be perfectly flat, free from any voids or surface defects, and as free from seasonal wood movement as possible. Plywood is an excellent choice, but you need to select high quality plywood that is free from internal voids. MDF is a wonderful substrate for veneer because it is dead flat, free from any internal voids, and will not change dimensions seasonally.

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The picture above is a piece of MDF that I’ve applied 3/8 thick mahogany edge banding to. Later I’ll use a hand plane to bring the edge banding exactly to the surface of the MDF, and eventually glue the veneer on top of the edge banding, giving the illusion of solid wood.

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Thursday, July 5, 2012

Veneer - A mystery to most modern amateur woodworkers


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Most amateur woodworkers and many professional woodworkers have never used wood veneer in a project. But most of us have used plywood products in our projects. And we all know that plywood is made from veneer, usually oak, cherry, maple, and to a lesser extent, more exotic woods like walnut. Plywood is also available in some tropical hardwoods, but finding it is exceedingly difficult. For my Mahogany entertainment center, for example, I need plywood made with very fine South American Mahogany veneer. I seriously doubt such plywood even exists in a commercial product, but if it did, I would expect it to be extremely expensive. So I really only have two options: I could make the entire project out of solid Mahogany. The problem doing this is very simple, Mahogany hardwood is very scarce and in my area, is priced starting at over $11.00 per board foot. And I would have to find enough solid mahogany that is consistent in color, figure, and free from defects, and in the thickness I need for each of the constituent parts. This would be a very expensive option and difficult option.

My other option is to make my own plywood out of high quality Mahogany veneer, which means I only need to find a relatively small amount of solid Mahogany for the legs, door styles and rails, etc. The very first class I ever took at the Marc Adams School of Woodworking was a class taught by Darryl Kiel, president of Vacuum Pressing Systems, on the basics of working with veneer. This class completely changed my woodworking life and taught me a wonderful and very different approach to woodworking. Even extremely scarce and exotic hardwood that would be impossible to find as solid wood is usually available as veneer. In fact, by turning precious and scarce hardwood into veneer, veneer manufacturers are effectively preserving a scarce resource. By learning to work with veneer, a woodworker is able to take advantage of this fact in his own projects.

Finding veneer locally, however, might be a challenge in itself. Small quantities of some veneers are available through woodworker stores like Woodcraft, but you will not find large quantities or scarce veneer. For that, I use Certainly Wood out of New York. They have a huge selection of veneers from all over the world, and have an extremely knowledgeable sales staff. There are numerous other sources on the Internet for veneer, but I have been very please with both the quality of the veneer I received from Certainly Wood and with their sales staff.

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If you do any serious work with veneer, a must have tool is a vacuum press.

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The vacuum press works on the principle that if you remove all the air from inside the bag, the weight of the atmosphere will press evenly on whatever is inside the bag. Depending upon your elevation above sea level, a vacuum press is capable of putting between 1500 and 1700 pounds per square foot of pressure on the object you are gluing. Here is a picture of some panels being pressed between two MDF platens:

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I purchased this vacuum press a few years ago from Vacuum Pressing Systems and have been very pleased with its performance. When I’m not using the system, the poly bag rolls up and is stored in a box and the vacuum pump lives in one of my drawers. The entire system can be put away out of site and takes up very little room in the shop.