Sliding Dovetails, When to Use Tapered or Straight

[HomerLee]

Is there a rule of thumb regarding how wide a board can be when using a straight sliding dovetail and when to use a taper? I realize at some point the straight dovetail becomes almost impossible to assemble.

[hbmcc]

HomerLee said:

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Is there a rule of thumb regarding how wide a board can be when using a straight sliding dovetail and when to use a taper? I realize at some point the straight dovetail becomes almost impossible to assemble.

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When it's impossible to assemble, try tapering.

This same question came up recently....

[EricU]

I think most people give up on straight dovetails after just 2-3"

[rwe2156]

EricU said:

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I think most people give up on straight dovetails after just 2-3"

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Yup. Its almost impossible to get them in after the glue is on.

[JimReed@Tallahassee]

I like sliding dovetails and I like T&G joints. I think they are very similar in function. Both of them make tight long joints that are able to keep their strength while moving. Glue for a joint like this is contraindicated. A sliding dovetail is intended to slide and glue prevents that.

How long the joint is varies with the project and the joint must be adjusted for length. Just like T&G, dovetails need room to move. Accordingly, the pieces should be constructed with sufficient slack. Longer joints need more slack because of irregularities in the wood. Sometimes wide boards bow and that can put incredible pressure on the joint.

As with all joinery, strength results from opposing forces. Sliding dovetails are pretty weak by themselves but can be very strong with used with other joinery techniques.

I made a walnut bonnet topped cradle using the Norm's NYW plan as a guide. The floor was T&G and the runners were sliding dovetails with an arched brace. Twelve years, multiple moves and two kids later, and the runners are still solid.

Sliding dovetails can add strength and beauty to your project. Good luck with yours.