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In preparing a glue joint, it's important to keep a couple of ground rules in mind. First, while modern glues are amazingly strong, if joints do not fit properly or the glue is not allowed to cure correctly, the bond will almost surely fail. And second, less is more. A thin, even layer of glue will form a strong bond between two pieces of wood, but a thick cushion of glue does just the opposite. It weakens the joint. And, usually you won't know if this joint is weak until the piece is done and has been used for a while.
Visit the Woodworking Plans Website pages for more woodworking articles.
To achieve a successful edge joint, the long mating surfaces must be perfectly tight all along their length. You shouldn't rely on clamps to pull bowed boards together because this places too much stress on the joint and eventually it will fail.
The fit of a mortise-and-tenon joint should also be precise, neither too tight nor too loose. If the parts must be forced together, there will be no room for the glue between the pieces and the joint will be starved. If, on the other hand, there is too much play in the joint, the glue layer will be too thick to perform properly when the piece is placed under stress. In a perfect joint, the glue layer is less than the thickness of a sheet of notebook paper.
In order to guarantee that there is sufficient glue in a joint, spread a thin layer on both mating surfaces. In a mortiseand-tenon joint, this means coating both the mortise and tenon walls with glue. You can use a scrap stick, a small brush or a narrow roller to do this. Just make sure the coverage is complete and even
.
The mating surfaces must also be clean, dry and free of contamination before you spread the glue. Oil, waxes and some chemicals, like silicone, will resist the glue. And dust and water can cause the joint to fail by preventing good contact between wood surfaces, or diluting the strength of the glue.
All glues have a recommended open time, which defines the amount of time you can safely leave the glue exposed to the air before assembling the joint. For most yellow glues, this is about 10 minutes. But the open time will vary with the temperature and humidity of your workroom. Hot, dry conditions will cause the glue to set quicker. In complicated assemblies, where many joints must be prepared at once, it's important to factor the open time limit into the process.
Sometimes, you'll have to assemble a project by making smaller subassemblies first. Also, keep in mind that yellow glue will not perform well in cold conditions. Most manufacturers recommend that both the room and the wood surfaces be at least 55 degrees F before applying glue.
Once a joint is assembled, it must be clamped together. Clamps serve two purposes. They pull a joint together tightly and hold it in a fixed position while the glue sets. You should not apply tremendous force with your clamps because this will drive too much glue from the joint. Just firmly tighten them and set the assembly aside.
If a proper amount of glue has been spread and a proper amount of force used to tighten the clamps, you should see small beads of glue squeezing out of both sides of the joint. To remove this squeeze-out, allow it to set for about 20 minutes, and then use an old chisel or putty knife to scrape off the excess.
Some people recommend wiping the excess glue off with a damp rag. But this technique should be avoided because it can force glue into the surrounding wood pores–especially with open-grain woods. Unfortunately, this glue will not be apparent until you apply the finish, when it's too late to do anything easily to fix it.
Finally, yellow glue should be allowed to set for at least an hour before you remove the clamps. And a full cure takes at least 24 hours, so don't isturb the assembly until this time has passed.
Visit the Woodworking Plans Website pages for more woodworking articles.
To achieve a successful edge joint, the long mating surfaces must be perfectly tight all along their length. You shouldn't rely on clamps to pull bowed boards together because this places too much stress on the joint and eventually it will fail.
The fit of a mortise-and-tenon joint should also be precise, neither too tight nor too loose. If the parts must be forced together, there will be no room for the glue between the pieces and the joint will be starved. If, on the other hand, there is too much play in the joint, the glue layer will be too thick to perform properly when the piece is placed under stress. In a perfect joint, the glue layer is less than the thickness of a sheet of notebook paper.
In order to guarantee that there is sufficient glue in a joint, spread a thin layer on both mating surfaces. In a mortiseand-tenon joint, this means coating both the mortise and tenon walls with glue. You can use a scrap stick, a small brush or a narrow roller to do this. Just make sure the coverage is complete and even
.
The mating surfaces must also be clean, dry and free of contamination before you spread the glue. Oil, waxes and some chemicals, like silicone, will resist the glue. And dust and water can cause the joint to fail by preventing good contact between wood surfaces, or diluting the strength of the glue.
All glues have a recommended open time, which defines the amount of time you can safely leave the glue exposed to the air before assembling the joint. For most yellow glues, this is about 10 minutes. But the open time will vary with the temperature and humidity of your workroom. Hot, dry conditions will cause the glue to set quicker. In complicated assemblies, where many joints must be prepared at once, it's important to factor the open time limit into the process.
Sometimes, you'll have to assemble a project by making smaller subassemblies first. Also, keep in mind that yellow glue will not perform well in cold conditions. Most manufacturers recommend that both the room and the wood surfaces be at least 55 degrees F before applying glue.
Once a joint is assembled, it must be clamped together. Clamps serve two purposes. They pull a joint together tightly and hold it in a fixed position while the glue sets. You should not apply tremendous force with your clamps because this will drive too much glue from the joint. Just firmly tighten them and set the assembly aside.
If a proper amount of glue has been spread and a proper amount of force used to tighten the clamps, you should see small beads of glue squeezing out of both sides of the joint. To remove this squeeze-out, allow it to set for about 20 minutes, and then use an old chisel or putty knife to scrape off the excess.
Some people recommend wiping the excess glue off with a damp rag. But this technique should be avoided because it can force glue into the surrounding wood pores–especially with open-grain woods. Unfortunately, this glue will not be apparent until you apply the finish, when it's too late to do anything easily to fix it.
Finally, yellow glue should be allowed to set for at least an hour before you remove the clamps. And a full cure takes at least 24 hours, so don't isturb the assembly until this time has passed.
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