Last week I received the new (latest!) F3 finger joint template for the Leigh D4 dovetail jig, for evaluation.

I love to make boxes; as a result, the D4 jig I bought many years ago has always been the workhorse in the shop. This has always meant that until now all my boxes used dovetail joinery – through dovetails, inlaid dovetails, sliding dovetails, half-blind dovetails. The F3 will make it very easy to make boxes with finger joints; now I will make them very, very easily.

The F3 mounts on the D4, and replaces the dovetail finger assembly completely. That is what the 15-second opening sequence of the video at the bottom of this article is about. Simply remove the dovetail finger assembly, and replace it with the F3. What could be simpler than that? Step-by-step, the following is what I did:

1. Replace the dovetail finger assembly with the F3 finger assembly
2. Install the e7 e-Bush on the router; select a setting of 5 to start the test cuts
3. Select board width for a box around 4 inches tall; rip to final width, per the board width selection guide on page 12 of the User Guide
4. Test boards, to test the finger joint fit: Make the first tests at a setting of 5 on the e-Bush; make sure to run the guidebush on both sides of each template opening, to get even cuts on each finger on the boards
5. Adjust the joint fit by rotating the e-Bush as needed; each division adjusts the joint fit by 0.002″
6. I found that a maximum of three tests was required to fine tune the perfect fit.

For purposes of this first video on the F3, I made a box using symmetrical box joints. This means that two of the boards have pins on the side edges, and two have sockets on the side edges, like the two boards in the back in the following image (I copied the following image from the 15.9-MB F3 User Guide):

F3 symmetrical vs. asymmetrical joints.

To make the symmetrical joints, the User Guide includes on page 12 a chart that simplifies the process of selecting board width, for optimum finger placement:

F3 board width selection chart.

One important thing to remember when making this joint: After cutting the joint on the ends, the boards are rotated end-over-end, not clockwise or counter-clockwise. This maintains the symmetry.

Using this chart: I decided I wanted to make a 5/16″ symmetrical joint. The maple boards I had on hand were just over 4 inches wide. From the chart, and circled in red, I determined that the boards would have a total of 11 fingers, and the exact width required would be 3-17/32″. I ripped the boards to that width, and it worked beautifully! But you will have to watch the video below to confirm this.

Disclosure: Leigh Industries is a sponsor of this blog. On occasion, I receive tools and jig templates for evaluation; and I maintain total editorial freedom of the reviews I present on the blog. Plain and simple, I never receive or accept cash for anything I review.

The F3 finger joint template — symmetrical joints
Download this video in Quicktime format
(In Windows, Right-click | Save Link As…)
Duration: 28:29 minutes
File size: 248 MB

I would love to hear from you how you cut the finger joints for the boxes you make:

• Do you use hand tools?
• Do you use a dedicated jig?
• Do you make the joints on a table saw or on a router table?

Acknowledgment: Music courtesy Jason Riley, professional guitarist, St Joseph, Missouri, USA. I selected Track #8 in the Outtakes CD – It is Prelude in D, by J.S. Bach).

— Al Navas