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Dowel Pins, The Difference
Expansible Dowel Pins
Compressed Loose Tenons
Tenons – The Difference
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Dowel Pins, The Difference
Dowel pins with cut straight multiple grooves
are manufactured using a moulder to cut multiple dowels from a wood strip. The resulting dowel will be shaped more like a lemon than a circle. The dowel can be out of round by as much as .020”. The reason for this; the tooling used is ground to a profiled during manufacturing and is sharpened by grinding only the tool face, because the profile is not re-ground no clearance angle can be ground into the tooling. The profile would change each time the face is re-ground if there were any clearance angles. When tooling profiles cut at 90° to the wood processed and don’t have any clearance ground into the profile the tooling has a tendency to burn the wood so the tooling is ground “splayed out” and not vertical to prevent burning, this forms a dowel that is shaped like a lemon and not round. Slightly more than half of the multiple dowel profile is cut from the top the other half is cut from below, releasing the dowels from the board. Should the wood move even slightly after being cut from the top the resulting dowel halves will be shifted sideways and further out of round and out of tolerance.
Dowel pins with straight cut multiple grooves
will expand as they absorb some of the glue moisture but because they have no compression to release, will shrink back to their original size as the moisture dissipates breaking some of the bonds between wood and pin. Because the grooves are straight they can be withdrawn as time and stress compromise the joint acting like a spline.
Smooth dowels with a single spiral groove
are manufactured with a centerless lathe, sometimes the spiral groove is cut during manufacturing and sometimes the spiral groove is cut into an existing smooth dowel. This is a way of re-cycling short lengths of smooth dowel into another product. They will release hydraulic lock but the smooth surface can’t retain much if any glue needed to form a chemical bond.
The JustJoinery ® brand Expansible Dowel Pin ®
is manufactured using a centerless lathe, the dowel is cut oversize and then multiple helical grooves are compressed into the dowel during the same process. This produces a dowel pin that creates not only a better mechanical fit but also a better chemical bond between the wood, dowel pin and glue. Wood has a memory, compress it when it’s dry and the dowel pin will expand again using some of the glue moisture, most of this expansion happens in the helical grooves. Water based glues are not 100% solids and shrink during curing. The Expansible Dowel Pin® grooves are expanding as the glue is shrinking. A chemical bond is formed where there is about .003” of glue between the wood and pin. That happens on either side of each high point on the pin. The glue spread is also enhanced by the helical grooves as the pin is inserted.
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