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Asymmetric Dovetails
CHAPTER 13
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Chapter Foreword For certain procedures, you will need touse both ends of the Leigh jig. Asymmetricaljoint layouts are one example. On the LeighJig, no joints will be truly symmetrical, butthey can look symmetrical. Apparent sym-metry is only required for aesthetic reasons,and not for strength. Be sure you have readand understood chapters 8 through 11before attempting these procedures.
13-1By symmetrical we mean a joint that looksor is approximately symmetrical about itscentre line but is probably not, and neednot be, precisely symmetrical. Using theLeigh jig, it is easy to cut a joint that lookssymmetrical; the pins will always align per-fectly with the tails cut at the same spac-ing. Remember, symmetry is only requiredfor appearance, not for joinery reasons.
13-2By asymmetrical we mean a deliberatelyuneven layout of pins and tails required bythe project design.
13-3For example, asymmetrical joints may beused for blanket chests or boxes. One pinis made wider for a saw-cut allowance, sothe half-pins all look the same width afterthe lid portion ➀ is cut off.
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13-4In the chest example you can see that if bothends of the board are cut under the sameguidefingers, the wide sockets and pins atopposite ends will not line up. Remember,the same inside face i of the through dove-tail tail board has to face away from the jigfor each cut.
13-5Deliberately asymmetrical joints must there-fore be routed on both ends of the jig usingtwo separate, almost mirror-image layouts.
13-6The layouts need not be exact mirrorimages because the parts that fit togetherwill be made on the same end of the jig.For a typical blanket chest you wouldrout corners A and C on one end of thejig and corners B and D on the otherend.
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13-7Here is an easy way to cut these near-mir-ror-image joints. Lay out the A and C cor-ner joints in the usual way (i.e., in the dTD PINS mode). Rout the A and C cor-ners’ tails and pins. Leave the guidefingersset and in the dTD PINS mode.
13-8Take a square-cut scrap board wide enoughto clamp horizontally in the front clampand as long as (or slightly longer than)the width of the workpieces, and butt itagainst the same side stop you used for theA and C joints. Mark the board to indicatewhich face o is out on the jig.
13-9Pull the finger assembly forward until thebracket line is on the highest scale reading.
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B/D
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13-10Mark pencil lines across the top edge of thescrap board, along the bottom of each sideof each guidefinger or pair of guidefingers.
13-11Turn the board (like turning a page of abook) to the other end of the jig and againstthe side stop, so the inside face i is nowaway from the jig. Adjust the guidefingersat that end to match the pencil lines.Note: See the next page for how to transferhalf-blind mirror-images.
13-12Now rout the B and D corners’ tails andpins using this guidefinger pattern. Whenyou assemble the case, the A and/or C endswill fit each other, and the B and/or D endswill also fit each other. Keep the boardsinside face i inwards on the case and theside-stop edges all turned the same way,and the parts are sure to match (see 13-6).
B/D
A/C
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13-13A quicker and only slightly less accurateway to “mirror” the guidefinger positionsfrom one end of the jig onto the other endis to simply flip a completed A or C pinboard from one end of the jig (like turninga page) to the other end, and centre eachpair of guidefingers over a pin. (This is notso precise because you are aligning con-verging angles of pins and guides insteadof straight lines.)
13-14To transfer a mirror image asymmetricalhalf-blind joint, first set the scale on1”[25mm] in the H HB TAILS mode.Mark pencil lines next to the tail guides,and...
13-15Turn the marked board (like turning a pageof a book) to the other end of the jig. Positionthe guidefingers over the pencil marks.
This tail board layout may look symmet-rical, but as the next illustration shows, itforms part of an asymmetrical joint.
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13-16This common example of asymmetry iswhere boards are of a different width. Inthis case, a drop-front drawer, the drawerfront bottom half-pin is much wider thanthe top half-pin. The top edges of the draw-er front and sides are flush, so it makes senseto use these edges against the side stops ateach end of the jig.
13-17 Mount the right hand r drawer side on theleft end of the jig for routing, and...
13-18Transfer the joint layout from left to right(as in Figure 13-14 & 13-15).Mount the left hand l drawer side onthe right end of the jig.
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13-19Mount the right end r of the drawer fronton the left end, and...
13-20Mount the left end l of the drawer fronton the right end, using the mirror-imagelayouts on both ends.
13-21Both ends of the jig are also used for thetop corners of a slant-front desk. The jointsthemselves may be symmetrical, but theymust be routed on opposite ends of the jigbecause the sloped front will not registeraccurately against the fixed side stops.
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13-22At the back of the desk both sides andtop are flush, so the rear edges are set againstthe side stops. Place the left end l of thetop tail board against the left side stop e.Rout the tails.
13-23The left side l of the desk goes against theleft side stop e. Rout the pins.
13-24Transfer the joint layout from left to right(as for 13-8 to 13-11) and place the rightend r of the top tail board against the rightside stop f. Rout the tails.
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13-25Place the right side r of desk against theright side stop f. Rout the pins.
13-26Note: If, in the slant-front desk example, thepins were in the desk top and the tails in thesides, then all the parts would be routed inthe opposite ends of the jig to those shownabove.
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