Tapered sliding dovetails

[DaveR]

Hi folks.
I like using sliding dovetails to attach table tops. I don't particularly like the "Oh curses, my joint is binding before it's fully seated" moments.
Reasonable suggested solution: tapered sliding dovetail.
However, something perplexes me about them - once the joint is closed surely it can only shift in one direction - i.e. Expand OR contract - depending on which end is fixed. If the wider end is fixed, the top would be able to expand - creating a loose DT. If the narrow end is the one that's fixed the top could contract - again resulting in a loose DT- but not expand from its starting dimension.
How do you folks get round this, or, more likely, what am I missing??!
Many thanks,
Dave

 

[Just4Fun]

What do you mean by "fixed"? Do you mean glued?

I have only used tapered sliding dovetails on a couple of projects but on those I didn't use any glue or other fixings. I just found the joint holds itself together perfectly well without. With the whole of the joint length free to move as it wants to I would not expect any movement problems. Nor have I had any movement problems but my projects are relatively recent (within the last 2 years) so it may be too early to claim success on that.

 

[thetyreman]

I've only used it once on a coat rack project, it's important to have a bit that's loose or it'd be close to impossible to knock in place, so about 2/3rds of it are under tension, designed so you can knock them out again. To attach table tops I use turnbuttons.

 

[dzj]

Best not to think about it really.
If you are using a batten to affix a tabletop (grain directions at 90 deg.), then don't do tapered DTs, but regular ones (slightly loose-fitting).
If their grain directions match, then go for the tapered variety.

 

[AndyT]

As far as I know, there are two main sorts of tapered sliding dovetails.

One is a variant on a plain housing joint. Typically used on the end of a horizontal shelf where it meets a vertical bookcase side. Grain direction is the same on both pieces so shrinkage will match. There's no reason not to glue the joint.

The other is where a batten is tapered in the width and along its length, so it can fit into a matching doubly tapered groove. Typically used to try and keep a glued up panel flat. Found on drawing boards, chest lids and small tables. Grain direction on the batten is at 90 degrees to the grain of the panel.

Historically, not used much in English furniture as it was in continental Europe. (In Germany they developed special planes for the purpose.)

I think this must be the sort you are thinking of but I've not seen them holding a table top to its frame. Buttons, metal brackets or screws in oversized holes are the normal methods for that.

If the long battens are what you mean I'd leave them unglued but expect to knock them tight if seasonal changes made them loose.

 

[Chris Knight]

This issue of Fine Woodworking has an article on sliding dovetail battens (cleats as the Muricans call them) for tabletops.

#213–July/Aug 2010 Issue. You will probably need a digital sub to download the complete article.