Leigh Industries are best known for their high-end variable finger spacing dovetail jigs – they invented them after all – that let you cut the full range of dovetail joints in any pattern you like. Dovetail jigs like their flagship Leigh D4R-PRO are designed to be mounted to your work bench and the dovetails cut using your router freehand. With the LEIGH RTJ400 Router Table Joinery Jig they’ve reversed the process with the router mounted in your router table and the stock held in the jig and fed onto the cutter to produce fixed width through dovetails, box joints and half-blind dovetails. The Leigh RTJ400’s approach to cutting box and dovetail joints eliminates the need to hold and maneuver your router through the fingers of a traditional jig.
The LEIGH RTJ400 Router Table Joinery Jig has several features that contribute to both its simplicity and versatility and allow you to rout a number of different sizes of through dovetails, box joints and half-blind dovetails quickly and easily.
At the heart of the Leigh RTJ400 is a 27″ long precision CNC-machined aircraft grade aluminum, double-sided template that allows you to cut both the tails and pins for a through dovetail, and acts as a base for the clamping frame which sits in a T-track in the template and accommodates boards up to 16″ wide.
At the ends of the template, there’s a series of preset holes and slots for routing different types of dovetail and box joints which is what makes the jig so easy to set up and use. These holes are used to position the frame on the template for each type of joint. If you want to cut through dovetails, for example, you position the frame using the corresponding presets on the template. Then, when it’s time to rout a different joint, you simply switch to a different set of holes.
When assembled the Leigh RTJ400 weighs 11 lbs making it light enough for portability and ease of movement over the router table, but still with sufficient heft to keep it firmly in place on the table as you rout the joints.
The elliptical guide bushing is another Leigh innovation that contributes to the jig’s versatility and precision. It has an opening with an elliptical shape, rather than a perfect circle like normal bushes. When routing dovetails, almost every joint requires some degree of fine-tuning to get the fit just right and the elliptical bushing provides a means of making super-fine adjustments as small as .001″. When rotated, the effective diameter of the barrel changes. If the joint is too loose or too tight, you fix it by rotating the bushing – too loose, turn the eBush to a higher number (clockwise), too tight, turn it to a lower number (counter-clockwise). To make it completely foolproof, the directions ‘tighter’ and ‘looser’ and marked on the bushing itself. For increased precision, mark a centerline on the reducer ring that holds the bushing so that you have an easy reference for adjusting the bushing based on the cut at hand.
The Leigh RTJ400 holds workpieces up to 16″ wide using spring-loaded clamps that slide in a track and hold the workpieces securely to the frame as you rout the joints, and adjustable side stops allow for accurate positioning of the workpiece. The side stops even have a built in offset for half-blind dovetails which also means you can work with rabbeted drawer fronts.
The clamps work well and hold the work securely against the textured, non-marring surface and in theory you can rout boards as long as the height of your ceiling will allow (the video below demonstrates working with a tall board). A limitation of using a traditional bench mounted dovetail jig is that the length of board you can easily work is limited by the height of your jig above the floor. Obviously wide, tall boards are heavier and will make it more difficult to keep the RTJ400 completely flat to the router table.
A few more useful items come with the Leigh RTJ400 that make life easier. You get 5 quick reference instruction strips that slide into the top of the jig. The RTJ400 comes with a comprehensive instruction manual like all Leigh dovetail jigs as well as an instruction DVD, but the quick reference instruction strips are very useful and on hand at all times.
Given the number of joints the RTJ400 can produce, you’ll need a number of different router bits and so it comes standard with four different bits, which can be used to cut through dovetails, half-blind dovetails and box joints. An accessory kit is also available with more bits and bushings to expand the capabilities of the jig.
The component we really like is the little red blockers that fill gaps between the template fingers depending on what joint you are cutting. There are 2 situations when you’ll want to use these and they help stop you from making expensive mistakes in the middle of your project.