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Exact-fit dado jig

 

An exact-fit dado jig, built with the WoodAnchor fixturing system

Overview

The WoodAnchor™ exact-fit dado jig enables you to cut dados to the precise width you need, using a just one standard-sized router bit.  Regardless of the exact thickness of the mating workpiece, this jig can easily create dados that fit it perfectly.

The basic configuration of the jig is well known.  It has a head, a fixed guide fence mounted at 90° to the head, and an adjustable fence that controls the dado width.  Fence spacing is set directly from the mating workpiece material. A standard router guide bushing, mounted to the base plate of a handheld router, runs against the fences.  For a good tutorial on the basic jig configuration, check out this video by The Wood Whisperer.

WoodAnchor fixturing technology enabled us to solve several problems typically encountered with this basic jig design.

  • Topside fixturing slots eliminate the need for any hardware to protrude beneath the jig.  Unlike most shop-built dado jigs, this one can be placed flat on your workbench during use.
  • An optional built-in workpiece clamp solves some awkward clamping challenges.  Our jig design clamps itself directly to your workpiece.
  • Optional adjustable stops make it easy to accurately rout stopped dados.

How it works

To set the dado width, pieces of mating workpiece material are used as setup blocks.  Simply loosen the adjustable-fence mounting screws, sandwich the workpiece material between each end of the fences, and retighten the mounting screws.

To set up the workpiece clamp, place the head of the jig against the near side of the workpiece, and move the clamp head inward until its pad contacts the far side of the workpiece.  Then loosen the cam-axle mounting screw, position the cam against the clamp head, and retighten the screw securely.

With the cam axle in position, clamping the jig into position couldn’t be easier. Align the inside edges of the fences with the dado layout marks on your workpiece, and rotate the cam lever until snug.  The jig is now securely clamped to the workpiece.

A WoodAnchor exact-fit dado jig, self-clamped to a workpiece

To adjust a dado stop, measure the offset from the edge of your router bit cutter to the edge of your router base.  Then lock down the dado stop at this same offset from your dado-end layout line.  A simple wooden setup block, with its length cut to the measured router offset, makes setting the dado stop a very fast process.

Dado routing is performed in a clockwise direction.  Starting at the near side of the dado, hold the guide bushing against the left (fixed) fence while moving the router away from you.  When you reach the end of the dado, hold the guide bushing against the right (adjustable) fence, and move the router back toward you until the dado is complete.

The WoodAnchor™ advantage

The WoodAnchor system makes the special features of this new jig design imminently practical.

  • The ends of the adjustable fence are fastened to fixturing slots on the topsides of the head and the tail brace, using WoodAnchor sliding nuts.  No hardware protrudes through the bottom of the jig, where it could interfere with your workbench.
  • The adjustable-fence mounting screw holes are counterbored, leaving a completely unobstructed surface on which the router base and the dado stops slide.
A fully-recessed WoodAnchor fastener, which leaves the working surface free of obstructions
  • Each dado stop is mounted to a fixturing slot atop the adjustable fence, using a pair of WoodAnchor sliding nuts.  Alignment pins keep the nuts properly oriented when the stop is removed, making reassembly exceptionally fast and easy.
An alignment pin keeps a WoodAnchor sliding nut oriented in the desired direction
  • The pad of the sliding clamp head is located beneath the fixed fence, in line with the workpiece.  But the clamping cam is located on the top of the fixed fence, where it is easily accessible.  This configuration is possible because the clamp head is configured as a linear slide, attached with two WoodAnchor sliding nuts.
The built-in workpiece clamp on a WoodAnchor exact-fit dado jig
  • The high clamping force capability of the WoodAnchor system allows the cam-axle position to be infinitely adjustable, and yet still withstand the high lateral forces from the sliding clamp head.

Summary build notes

We plan to add replaceable edge guides to this jig design, so that any damage from router bushing misalignment can be easily repaired.  Following that upgrade, we’ll publish plans and build notes.