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The Leigh D4 dovetailing jig has to be the most ingenious tool I have purchased to date.
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Leigh D4 Dovetail Jig

The best there is

Text and photos by Tom Hintz

Note: This version of the Leigh Jig is no longer available as far as I know. The newer one, the D4R is very similar but has upgrades. Click Here to see my review of the D4R.  

See my Rolling Jig Work Station Plan! - Click Here!

 I had lusted after the Leigh jig for some time after seeing his Normness use it on The New Yankee Workshop. The price was one consideration, but I was hesitant in part, because the Leigh D4 looked like it could be complicated. Now I wonder why I waited so long, as I suspect many other new Leigh owners do as well.

Documentation

   When unpacking the Leigh jig, one of the first things I noticed was the thick instruction manual and 50-minute-long video.
   The video is instructive, well produced and provides a solid overview of the capabilities of the Leigh jig. Most importantly, this tape lets you see most of the operations being done which helps understand the procedures better when trying them yourself.

The Leigh instruction manual is the standard all others should be judged by.
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   The manual is quality of the first order. The spiral binding, (lays flat while open) paper and first-rate illustrations show Leigh was interested in producing the best instruction manual possible first and the cost second. The writing is easy to understand and the format guides the reader through all jig functions in a logical order.
   I attended a dovetailing seminar at the local Woodcraft store during which the instructor (who admitted not having experience with the Leigh jig) said the size of the Leigh manual indicated how time-consuming the Leigh is to set up. I disagree. The Leigh manual is the benchmark most other companies fail to meet.

Assembly

Assembly of the D4 is a snap. The packaging is also first rate.
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   The capabilities of this jig lead one to expect a lengthy and involved assembly process. The reality is this is an easy tool to assemble and set up. Everything is very well made and fits properly. The instruction sequence yielded no surprises and within 20 minutes, my jig was assembled and ready for the short alignment process.
   The only parts of the jig requiring alignment are the side bumpers that are set using short pieces of lumber. The only caution I have is to make sure the pieces of wood used for this step have accurately squared ends. If the boards are right, you are eight screws away from being done.
   The only problem encountered with the Leigh jig occurred when adjusting one of the bumpers. Turning the locking screw slid the bumper out of position. I used a needle nose pliers to hold the bumper while tightening the screw. Problem (using the term loosely) solved.

Mounting

I used the mounting bolts to index the jig off the edge of the bench.
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   The D4 has a slot along the underside near the front for t-bolts (5/16-inch bolts fit as well) meant to secure the jig to a bench top or clamping board. I bolted my D4 to a piece of ¾-inch-thick 8X36 inch poplar. Holes for two 5/16 by 1 ¼-inch-long bolts were drilled so that the clamp board is held back from the front edge of the jig by about 1/8-inch. I drilled a countersink with a forstner bit to recess the nut and washer, but left the remaining bolt protrude. These act as stop-pins when I clamp the jig to the bench, making sure work pieces clamped in the jig are well clear of any obstructions below.
   A pair of quick clamps secures the jig and board to the bench top.

Testing (Play time)

The joints above were all done within the first hour after assembling the jig. This tool is easy to operate!
Note: Only the sliding dovetail (bottom) was sanded (It was invisible), the rest are just as they came out of the jig.
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   I purchased the Leigh jig kit that included two dovetail bits (#120-8, 14-degree - ½-inch,#80-8, 8-degree - ½-inch) and one straight bit, (140-8, 5/16-inch cutter) all with 8mm shanks, and the 7/16-inch collar which fits my Porter Cable 690 router. Also included is a collet reducer to fit the 8mm shanks to the ½-inch router collet. Again, everything is well made and fit perfectly. When ordering a Leigh D4 dovetail jig, you will be asked what router will be used with it and the kit tailored accordingly.
   The manual begins with through dovetails, and then moves on to the various half-blinds, then to sliding dovetails. I suggest following this progression as it helps build familiarity with the jig, it's functions and adjustments in a logical order.
   The first step is to arrange the fingers for the wood being used. I cut several pieces of wood, all the same width and thickness. This allows one finger arrangement to be used for all joint types.

Through Dovetails

   If you follow the instructions, the chances of making bad through dovetails with this jig diminishes greatly. The one critical step is setting bit depth, but that is relatively easy. Having the bit a little too deep only means slightly more sanding time to bring the pins flush with the surface. My first set extended beyond the surface approximately 1/32-inch.
   The fit was nearly perfect with the only error being very slight at the outboard edges of the board, caused by a noticeable cup in the wood. Slight clamp pressure corrected the alignment problem easily.

Half-Blind Dovetails

The adjustable fingers mean the possibilities are endless with the Leigh jig.
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   Using the same finger configuration, I tried a set of half-blind dovetails. In the past I could make good half-blinds, but it often took several setup attempts to get the fit right. The Leigh also requires setup, but the simplicity of this jig shortens that time considerably. I have re-installed the dovetail bit for half blinds four times now, none of which required a third test cut to get the fit I want.
   My first set of half-blinds went together, but were a little tighter than I liked. I made one height adjustment to the router and cranked out eight sets of perfect half blinds in minutes. I did so many to see if anything would change in a mock

The indicator scales are pure genius, and make mistakes almost hard to make.
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production run. Nothing did and the joints were interchangeable among all the pieces made.

End-To-End Dovetails

   I have tried end-to-end dovetails in the past with little success, and that after considerable searching for the setup. With the Leigh D4, end-to-end dovetails are made with the same setup used for half-blinds, except that both pieces are routed in the vertical position with the finger assembly aligned to a special mark on the indicator.
   The first set of end-to-end dovetails fit perfectly, with both outboard edges of the boards aligned perfectly.

Sliding Dovetails

I opted for the kit that comes with three 8mm-shanked bits and the right collar for my router. I wasn't sorry.
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   Whether you want to make full-length (up to 24-inches long) sliding dovetails, or stop dovetails, they are easy to do on the Leigh. There is slightly more setup required, but the instructions get you very close. When making my first sliding dovetail, I had to make two adjustments to get the dovetail right.

Tips for Using the Leigh Jig

   There are a few things to keep in mind when using the Leigh. See my companion story - Click Here

See also my article on the Leigh Dovetail Jig Manual - Click Here

Click Here to see my review of the updated Leigh D4R.  

 

 

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