In this month’s FWW article on the tilt top table, the author says that the sliding dovetail (used to join the legs to the pedestal) is the “traditional and most effective” joint. I understand the traditional part, but I’m not clear on why it is the most effective, e.g. I thought that mortise and tenon joints are always the strongest.
I also noted that Norm (NYW) used the sliding dovetail joint on his recent dining room table and reinforced it by adding metal straps on the bottom (between the legs and pedestal)- would an M&T joint also require that extra reinforcement?
Thanks in advance for your comments.
Replies
I think that clamping the tenoned leg to the round bottom of the leg could be a problem. The sliding dovetail requires no clamps. I always use a sliding dovetail with a slight taper.When it goes all the way in it is tight and needs no clamps.The down side is that if for some reason a sudden jolt applied to the leg could split off the side of the leg and post. I don`t know why this would happen,but anything is possible. The brass plate set in the bottom of the post will prevent this.Thank you,Mr.Croney,where ever you may be.Work safely ¬¬¬¬¬¬¬¬¬¬PAT¬¬¬¬¬¬¬¬¬¬
Edited 10/21/2004 3:41 pm ET by Pat
Norm always uses metal to reinforce his joints..."and now I'll add a few hundred nails just in case...blam...blam...blam...blam...blam...blam...blam..." I bet he wears both a belt and suspenders.
Am I alone in this? I never jam nails into my joints, never. Furthermore, I have never had a failure either. In fact when I do repairs for people I always find joints held with metal fasteners fail long before the glue joints, am I right?
All those nails in what look like very fine & tight joints cut with the best machines on the market seem to indicate a lack of confidence on the builders part. Perhaps the nails/brads are used to reassure those without the skills or tools to construct such fine joints that work can proceed. Hard to imagine one of those half hour shows spending time on showing how to correct a poor joint, or making a new piece to replace on that did not turn out quite right. I bet many of use have lost our cosntruction schedules when we blew a mortise or tenon or cut or whatever, and had to do additional piece(s) on a project.
Charlie,
To start with a smart alec remark, the reason it's traditional is that it's the strongest.
Here's why I think it is stronger in this application. The weight of the table will tend to push the dovetail more tightly into its socket. The flare of the dovetail keeps the mating surfaces of the joint in contact as the legs try to splay further apart at their feet. The tendency of this force to split the shaft is effectively overcome by fastening a three legged "spider" to the underside of the shaft and legs, for insurance. The use of the spider is traditional also; I have an early (1740ish) Pennsylvania tip and turn table that has its original wrought iron spider, the legs of which extend several inches down the underside of the legs. It's attached with hand forged nails. When I restored this piece in the early '70's, I didn't bother trying to take the base apart, because it was as tight as the day it was glued up.
In contrast, a mortise and tenon joint (or dowels) will tend to be pulled apart by the forces applied to the joint. There typically isn't enough room in this area to allow for long and strong tenons, and the geometry of the leg entering the cylindrical shaft doesn't lend itself very well to pinning the joint either. It's the same reason you wouldn't mortise a drawer front and tenon the drawer side.
I've seen the mortise and tenon joint recommended for tripod table legs in one of Gottshall's books, but have only seen it on one rather crudely made, "country" table brought to my shop for repair. It too had split out at the base of the shaft, after its leg joints had been "pinned" with several 10d nails.
Gottshall theorizes that the mortise and tenon isn't used in this application because of the difficulty in clamping the curved, shaped leg, and recomends leaving the leg's outer surface flat at the time of glue-up, and shaping it later. Of course, clamping these legs in the course of a repair is just as problematic- it is worthwhile in my opinion to have a thought for the poor guy or gal who will be restoring our stuff 100 yrs from now. Why make it harder on them?
Regards,
Ray
To All,
Ray in the preceding post, explains clearly why a dovetail with a metal spider on the bottom is traditionally used for this application.
The leg to pedestal joint is fairly unique in woodworking design, it is one of the few joints that has considerable tension on it rather than compression or twisting forces. Most wood joints don't resist resist tension well, dovetails being one of the best under tension, but their shallow depth and end grain in the tails still makes them relatively weak for an application as demanding as the legs of a pedestal table.
Adding a spider at the bottom of the post, right where the stress is the greatest, is an elegant and highly practical solution to getting a strong joint in a difficult location. It is definitely not, as some have implied, made necessary by poor joinery.
The advantage of using a spider has been proven in use over several centuries. The sliding dovetail joint, with a metal spider, was commonly used by the Shaker cabinetmakers on their justly famous pedestal tables, which is about as good an endorsement for this joint as you can find.
John W.
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