Bring the adjoining piece of lumber up against the transfer plugs and the point of the dowel center transfer plug will mark the center positions of the holes in that piece of lumber, as shown in Figure 7.
Note 2: It is recommended that a minimum of two dowel pins be used at any single joint. This prevents the boards from twisting once joined.
Figure 7 - Dowel transfer plugs positioned in wood pieces
Although the use of dowel center transfer pins does increase the accuracy of aligning the dowel holes. They still leave a lot of room for potential errors and misalignments.
The best way to ensure that the pieces of wood are in alignment is to use a doweling jigs. There are numerous models of doweling jigs available as shown in Figures 8a, 8b and 8c. As a general statement, the more expensive the doweling jig, the more accurate the dowel hole position and the easier it is to use.
The biggest advantage of the doweling jig is that it provides a method of transferring the hole alignment from one piece of lumber to another. This prevents any possible errors in having surfaces and/or edges out of alignment.
The primary features that are important in a doweling jig are:
- It should provide self-centering on the wood being drilled. Some of the less expensive doweling jigs require the operator to center the jig on the piece of lumber to be drilled. This is a time consuming process and subject to error.
- It should have hardened steel bushings as the guide for the drill bit. Some of the less expensive doweling jigs are made of steel or aluminum and do not utilize bushings in the jig as a guide for the drill bit. Without steel hardened bushings, over a period of time, the drill bits used will widen the guide hole for the drill bit. Once the drill bit holes are wider than necessary, you have the potential of alignment errors or problems.
- If you are going to use the doweling jig for more than one project it is wise to purchase a unit that has the flexibility to locate different sized dowel pins.
Selection of doweling jigs.
Figure 8a - Self centering doweling jig with bushings
Figure 8b - Self centering doweling jig for thick lumber
Figure 8c - Precision doweling jig
Applying Glue When Using Dowel Pins:
Many home handymen are under the impression that when using dowel pins, glue is applied only to the surface of the pin and/or in the dowel pin hole.
This is incorrect. Yellow carpenters glue should be applied to both the dowel pins and the mating surfaces of the wood being joined together.
Figure 9 - Surfaces to receive glue when using dowel pins
Dowel pins are not pieces of doweling. Doweling is generally smooth, as shown in Figure 11, whereas dowel pins, as shown in Figure 10, have grooves cut in them to allow for more surface area for the glue to adhere to. For the best joints, proper dowel pins should be used, not pieces of cut doweling or smooth doweling pins.