Decorative Dovetails with the Incra System

Wood Joinery: The "Game Box" article, which appeared in August/September 2006, Issue #43, showed some sweet decorative dovetails. The dovetails generated a lot of interest among our readers. So we asked Kevin to give more detail on using the Incra jig.


Decorative Dovetails with the Incra System

Illustrations by Mike Del Rizzo

In this article Kevin shows you how to cut such dovetails using the Incra LS Positioning fence system. This system creates beautiful dovetails as well as complex and beautiful box joints. It can also be used for sliding dovetails, rabbet cuts, or dados. It's use is not limited to your router table but can be moved to the table saw, band saw, or drill press. This jig delivers unbelievable accuracy and flawless repetitive cuts.

The joint featured on the game box is called a Corner Post Double Dovetail. It's one of dozens you can make with the Incra jig using the templates in the accompanying master reference guide.

The LS Positioner takes no more than 30 minutes to assemble and mount to your router table. It's made from aircraft grade aluminum milled to machine shop standards, then hard anodized for long wear life. The accuracy and repeatability of the system comes from Incra's patented lead screw technology (hence the LS in the name) which comes from the 32 tpi (threads per inch) lead screw that the system is based on. It gives you incremental positioning in 1⁄32" steps as well as micro adjustments of 1/1000" (accurate to .002") over the full range of the Positioner. The standard system comes with a LS Positioner carriage and base, 28" Pro Fence, 13" telescoping extender bar with stop, right angle fixture, shop stop positioner and the master reference guide and templates.

Like any woodworking project it is very important to begin with stock that has been milled true and square. In the game box project I used ⅜" thick stock to make the corner post double dovetail, with padauk and maple as my contrasting wood colors.

• To begin this joint you first choose the dovetail template you wish to use as well as the corresponding bit. In my case it was template IDDB with a ⅜" 9º dovetail bit. You will then need seven pieces of wood, four pieces for the front, back and sides plus one piece for the corner post and one for the trim section (using a contrasting wood) and one for centering. All seven pieces must be of equal width and thickness. The front and back pieces must be of equal length, and the two side pieces must also be of the same length. The corner post section must be the same thickness as the front, back, and sides.

• When using the jig you will be making a series of cuts referred to as A, B, C and D. A cuts refer to front, back and side pieces. B cuts refer to the cuts along the trim section stock. C cuts refer to the front, back and side pieces after a rabbet cut has been made on them. D cuts refer to long cuts on the corner post section.

• Each template may call for a different size dovetail bit, from ¼" 7.5º to ¾" 7º, depending on stock thickness. Different size straight bits are used for decorative box joints.


The Dovetail Cuts
• Draw a pencil mark at the approximate middle of the centering piece of wood.

• Lock the router fence when you think you have it centered on the dovetail bit and, using a push block, run the stock past the bit, flat side down.

• Rotate the piece and run it over the bit again.

• Turn off the router and turn the bit so the cutters are 90º to the fence and place the stock just behind the cutter.

• Engaging the micro adjust feature, adjust the fence so an equal amount of clearance remains on both sides of the cutter. Your stock will then be perfectly centered.

• Insert the template you are going to use and set the template to the "Center Cut". For the IDDB template I used this was setting 9B.

• Set the height of the bit with some scrap stock the same thickness as your project wood (as described in the Master Reference Guide, which comes with the LS Positioner System). Remember to raise the bit to tighten the joint and lower it if the joint is too tight.

• Start by using your contrasting coloured wood to make the cuts for the trim section. These will be the B cuts on the template. The stock will sit flat on the table while you run the stock over the router bit. Move to the next B cut and repeat. For my game box it took two passes to complete this task.

• Place all four front and back pieces with a backer board against the right angle fixture.

• Put a pencil mark on the sides that are against the fence.

• Make the A cuts.

• At the table saw cut eight pieces from the trim section making sure they are just slightly longer than the thickness of your backs and sides.

• Glue the trim sections to both ends of the front and back, clamp, and allow them to dry for several hours.

• Sand the trim sections flush with faces.

• Place a line 3⁄32" from the outermost glue joint and cut along that line at your table saw with a crosscut sled or mitre gauge.

• Cut dovetail rabbets on one of either the two side pieces or the two front and back pieces. Remember to sneak up on these cuts 1⁄32" at a time to prevent tear out. The final depth for this template is ⅛".

• Place all four pieces against the right angle fixture and make the C cuts as shown on the template.


The Corner Post Section
• To add the Corner Post Section make the D cuts along the length of the corner post stock starting with an outside pass moving in towards the bit with each subsequent cut. Remember to use a rubber soled push block for safety.

• At the table saw cut four pieces of wood from the corner post section just slightly longer than the thickness of the front and back.

• Glue the four pieces to both ends of the non-rabbeted pieces.

• After they have dried belt sand these pieces flush with the faces of the two sides.

• Cut the pins to mate with the two rabbeted 'tail' pieces. Set the Incra stop as close to the bit as possible and make the D cuts. Assemble one section dry to see how far to adjust the stop to get a perfect fit. Move the stop away from the bit and make the cuts.

• Dry assemble before gluing to make sure everything fits well. Remember, that like any shop tool the more you use it the more proficient you will become. In no time you will be making beautiful joints for your projects. I know from experience you will be totally satisfied with your new Incra LS Positioner.

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Kevin Shantz