Loose sliding dovetails in winter

[Winston Chang]

While I was working on the table, I found this article in FWW by Andrew Hunter about attaching tabletops this way.
https://www.finewoodworking.com/2010/06/03/better-way-to-attach-tabletops

In it, he writes:

This taper eliminates the precision needed to fit a straightcleat and the need for glue. With no glue, you can remove thebase from the top if needed, and if the fit of the cleat loosens due to wood movement, you can tap it back home or remove and shim it if necessary. I’ve never had to do either because I start off with very dry wood and use quartersawn lumber for the cleat.

Now that I look at it again, I realize that the quartersawn part is important -- the wood that I used is cherry, which apparently moves twice as much in tangential direction compared to the radial direction.

For now, I may shim it with wood shavings or paper and see how it holds up after another year of changing humidity.

[Andrew Seemann]

I dug out that copy and took a look at the article. I don't know that I would call it a "better" way to attach a table top, maybe a different way, and subject to some limitations. FWW did some Cosmo-style headlines back then. That was about the point I canceled my subscription.

The climate thing plays into this again; he works out of Gardiner NY, and while not coastal, definitely milder than MN. Quartered wood would have helped, although it may or may not have helped enough. Trying paper shims and seeing what it does over the next year isn't a bad idea.

[Brian Holcombe]

Fantastic work! Was it assembled by sliding the battens into the top, and the putting that assembly on the legs?

Thank you, yes that is exactly how it functions.

I don't taper my battens anymore, I just size them to compress slightly, wax and fit. I agree with using quarter sawn but my issue with tapered battens is that they push the wood movement to one side and so half the batten is always loose (if the entire batten isn't already loose).

I dug out that copy and took a look at the article. I don't know that I would call it a "better" way to attach a table top, maybe a different way, and subject to some limitations. FWW did some Cosmo-style headlines back then. That was about the point I canceled my subscription.

The climate thing plays into this again; he works out of Gardiner NY, and while not coastal, definitely milder than MN. Quartered wood would have helped, although it may or may not have helped enough. Trying paper shims and seeing what it does over the next year isn't a bad idea.

I can't speak with Andrew specifically but here in NJ we deal with plenty of that issue. Only saving grace is that old houses sometimes leak enough and used radiators. Newer houses with forced air heat are brutal on furniture in these climates. He's not far from me relatively speaking and I'm certain that his environment also deals with these same issues.

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It's my opinion/experience that a sliding dovetail batten is not enough to hold up a table and keep it from racking. Heck, if you lean really heavily on one side of that table it may lever the leg enough to simply pop the wood right off the bottom between the top of the dovetail and the end of the board. It's not that strong.

The goal of dovetail battens, in my opinion, should be to help keep the table flat and allow it to move, that is all, it should be minimally structural.

Single dovetails, which is what a sliding dovetail batten is, are lousy against racking forces, they're basically a short splitting wedge attached to a huge handle.

[Derek Cohen]

Very interesting comments, Brian. This topic is of particular relevance for me as my current build plans to use tapered sliding dovetails to anchor the base for angled staked legs. I would not be overly concerned about this if the piece lived in my home, since Perth does not have a humid climate. However, it is going to live in Sydney, where no doubt there will be wide temperature swings and high humidity in summer.

What do you and others suggest: non-tapered sliding dovetail, ensure it is quarter sawn, and additionally secured with screws (with elongated slots for movement)?

Oh, the added base for the staked legs is necessary since they cannot go directly into just a case. The underside of the case needs to be built up in thickness. The sliding dovetail kills two birds with one stone - adds to the thickness and provides stiffness. It has to move as it is across the grain of the case, otherwise one could simply glue and screw a brace.

Regards from Perth

Derek

[Brian Holcombe]

Yes, that’ll help and I’d be tempted to add a stretcher, something that looked proper with staked legs.

[Tom Bain]

Brian — Do you happen to have a photo with the top on the table? Would be great to see the finished piece.

Here is a table I made over the summer. The sliding dovetails went in tight, they were about 40" wide and that was some work!

The tenons go into the table top, the sides of the tenons are made with clearance for seasonal movement but the large faces which bear against the end grain in the mortise are made tight (compression fit).

This table is rock solid, myself and my client pushing against the side could not get it to budge. The majority of that strength is in the tenons which enter the top, the table was merely strong prior. The dovetails do help but they're not relied upon to prevent racking movements.

[Brian Holcombe]

Thanks, Tom. Not yet, next time I head out there to that client’s location I will bring photo equipment.

[Lee Schierer]

I would guess that you didn't know the exact moisture content of the maple when you made the table. If your moisture was not at equilibrium with your environment then your problem could be due to normal shrinkage. Since the table is new and this is the first winter, I would wait and see what happens in the coming summer. If it is still loose, then the simple solution is to add a shim to tighten up the dovetail. If it tightens back up in the summer then it is strictly seasonal wood movement and you may have to look at a different solution. It might be worth while to determine how much further you would need to slide it together for it to be tight and seasonally adjust the table or add a smaller shim so you can keep the legs "centered" more closely with the seasons