Dowels
Q: What pressure should be used for plain & pre-glued dowel pins?
A: Generally, 10-20 psi is all that is needed for water to activate pre-glued dowels. If you have been using glue previously you may need to decrease the time that the glue valve is open to get a small enough amount of water. A good rule of thumb with glue is the higher the pressure the better.
Higher pressures will help the glue nozzles clean themselves. When they are kept clean they will perform much better. This is one exception to this rule: if you can't get a small enough amount of glue at a higher pressure you may have to turn down the pressure to avoid getting too much glue.
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Q: Will pre-glued dowels or water damage our panels?
A: Pre-glued dowels and water can damage panels if they are not used properly. Generally, the problem does not manifest itself in solid wood. You are more likely to see it in plywood panels. If the depth of the hole and the length of the dowel are proper, then there is no void left to trap water. If the holes are drilled deeper than necessary, then a place is provided to trap water. This water may then bleed through to the surface. To prevent this possible occurrence only two things are necessary: proper hole depth and proper dowel length. If used properly you will not experience any discoloration problems.
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Q: Are conventional or pre-glued dowels better?
A: A proper diameter dowel, in a proper diameter hole, applied by an automatic machine will produce a stronger joint with a pre-glued dowel than with conventional glue. This occurs because glue applied by an automatic machine does not coat the entire circumference of the hole, as water will.
Anytime an improper fit occurs because of the dowel or the bore, conventional glue will produce a stronger joint. The primary reason is because a pre-glued dowel will not fill any voids.
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Q: What would cause the dowels to be loose in the holes?
A: Dowels are loose for one of two reasons. Either the dowel is too small of the hole is too big. An 8mm bit does not guarantee an 8mm hole. Does the bit turn true? Has it been sharpened? Are your spindles out of tolerance? Are your dowel diameters too small? Additionally, an 8mm bit drilled into particle board; MDF, plywood and solid wood will give you 4 different sizes of finished holes. Some will be bigger and some smaller.
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Q: Is the length of the dowel pin determined by a ratio of the diameter?
A: On the small end of the scale you have a 5mm X 25mm pin which equates to a 5 to 1 ratio. On the large end of the scale you have a 5/8" X 5" pin which equates to an 8 to 1 ratio.
Generally speaking, the length of a dowel corresponds to a different formula. This is determined by how much dowel can be inserted into the shortest member of the two piece joint. Twice this length is a common rule of thumb for determining dowel length. As an example, if your shortest member is 1" thick and you know your safest drilling depth is ¾" then a 1½" dowel should be used. A 1½ length equates to two times the ¾" thickness.
A similar procedure can be used to determine a proper diameter for the dowel. Generally, there should be no space smaller than half the diameter of the dowel between any edge of the dowel and the outer edge of a panel. For example, if the side panel is 1" thick then you want to use a ½" dowel to adhere to this rule since that leaves ¼" on each side of the dowel.
Please keep in mind that these are general rules of thumb and that specific applications need to be addressed on an individual basis.
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Q: How deep should a dowel be inserted into the hole to be most effective?
A: Generally, a dowel should be inserted into the bottom of the hole. Occasionally, a small void may be advantageous to collect excess glue in order to avoid "blowout".
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