Drawbored Loose Tenons for Edge Joining

[Stanley Covington]

Richard Maguire posted an article on his website The English Woodworker about his mistrust of edge joints that rely solely on glue, and how he prefers to add drawbored loose tenons in addition to glue to reinforce such joints.

I will not post the excellent pictures from his webpage to this post, but urge you to take a gander at the article.

http://www.theenglishwoodworker.com/trust-or-reinforce/

It looks like a solid and even decorative way to edge join largish planks, such as thick tabletops, benchtops, and perhaps even some exposed structural applications. The latter is my primary interest.

I have used dowels, biscuits, slips, and even nails for the same purpose, but never a drawbored tenon, and am curious about several points, including splitting, potential difficulty in aligning the plank's top faces, and most importantly, the possibility of such large cross-grain tenons causing the joint to fail with dimensional changes to the boards due to humidity swings and exposure to rain.

Anyone have experience with this interesting joint?

Do you know if it used for shipbuilding?

Stan

[steven c newman]

The Greeks used for their ships.......

[Stanley Covington]

The Greeks used for their ships.......

Steve:

Thanks. Any idea where I can find a reference?

BTW, I used to live in Ohio, and it was said you could stand on a tuna fish can and view the entire state with a strong telescope. Where is the "Peak of Ohio?"

Stan

[steven c newman]

Look up the ships called Tiremes ( sp).....as in the navy from Athens that beat the Persians. There is now a replica of one of their ships in a museum.

Campbell Hill in Logan County, OH. Mad River Mountain Ski Resort is just south of there. I'm in Bellefontaine, OH. You can see quite a ways, from the JVS School located on that hill. Was the site of an Air Force Radar station, and I think one or two of the old Radome bases are still there.

[Stanley Covington]

I will look up the ships. Thanks.

I have been through Bellfontaine a few times. Nice town.

I used to live in Dublin, and later in Galena, a couple of hundred yards East of Alum Creek Reservoir. I wish I was there now to see the dazzling Autumn colors on Africa Road.

Stan

[Derek Cohen]

Stan

My concern with this approach is the introduction of additional stresses into the joining boards. The drawbore will pull the seams together. In a mortice and tenon, this is end grain to face/edge grain. On a tabletop it is edge-to-edge grain. Where there is not a good fit, and the drawbore pulls the seams together, will this introduce stresses that will be forced to escape elsewhere? I ask the question - I do not know.

Usually, when biscuits or Dominos or splines are used to align boards, my practice has been to glue just glue the one side, not both. Dovetails are used to stabilise, not pull together.

Lastly, is there any historical evidence of a drawbored, loose tenon tabletop?

Regards from Perth

Derek

[Stanley Covington]

Stan

My concern with this approach is the introduction of additional stresses into the joining boards. The drawbore will pull the seams together. In a mortice and tenon, this is end grain to face/edge grain. On a tabletop it is edge-to-edge grain. Where there is not a good fit, and the drawbore pulls the seams together, will this introduce stresses that will be forced to escape elsewhere? I ask the question - I do not know.

Usually, when biscuits or Dominos or splines are used to align boards, my practice has been to glue just glue the one side, not both. Dovetails are used to stabilise, not pull together.

Lastly, is there any historical evidence of a drawbored, loose tenon tabletop?

Regards from Perth

Derek

Thanks for the observations, Derek.

If the board's edges are not planed to match for a tight fit, or if the boards were sprung a great deal, then it seems clear the stresses you mentioned might be a fatal problem because the stresses on the pins close to the board's edges will tend to split the boards, especially if there is a gap between the boards that would allow the cracked edge to expand into relieving the stresses.

But if we assume both edges are planed to close tightly, as a good edge-to-edge joint should be, glue is used, and the loose tenons are only reinforcement perhaps intended to keep the boards tightly joined even if the glue fails, then it seems that the stresses might work. And if the drawbore work is done precisely, it seems that would not be a big problem since there would be no large space for the cracked edge to expand into since opposing edges would tend to contain any cracking induced expansion. Does that make sense?

Re historical examples of tabletops, I don't know of any, But I have seen large and heavy oak doors in cathedrals in Europe made of multiple shiplap boards joined with a rectangular cross section wooden stick, as long as the door is wide, and penetrating all the way through each board through aligned mortises/slots cut entirely through each board. The one I recall had 5 or 6 of these horizontal sticks (long, full-length, through tenons?) holding the door together, and pinned at their ends. As a matter of fact, there is a BBC program with Ruth Goodman about building a castle (Guidelon?) in France that shows part of the process of making such a door.

Not sure if they were drawbored or not. Not the same thing as what Mr. Maguire uses, but there are some similarities.

I have always thought it would make a cool table, but the chance has not presented itself. The loose tenons Mr. Maguire uses seem like an interesting alternative.

Stan

[Wayne Lomman]

This is a good concept. It doesn't introduce any different stresses that clamping and gluing any misaligned joint would have anyway. If done poorly, of course it will cause problems, the same way as poor work causes problems everywhere. I'll give it a go for sure. It's the first decent alternative to glue I have come across. Cheers

[Patrick Chase]

The Greeks used for their ships.......

Makes sense as they lacked waterproof adhesives back then. I'm less convinced that it makes sense now, or for less demanding applications like furniture.

[Pat Barry]

A variation on this technique works great for breadboard ends but is totally unnecessary for edge glued boards.

[Patrick Chase]

Richard Maguire posted an article on his website The English Woodworker about his mistrust of edge joints that rely solely on glue, and how he prefers to add drawbored loose tenons in addition to glue to reinforce such joints.

I think that the question one has to ask here is whether his mistrust is well-founded or even remotely rational.

Edge joints consist of a very large long-grain to long-grain interface with ~identical direction. Long<->long grain is basically the poster child application for glue, in the sense that it's the one and only case where it actually performs as claimed/advertised. The fact that the directions are the same (as opposed to something like the cheek interface of an M&T, which is also long-to-long but where they're at 90 deg) means that you don't have internal stresses that accumulate as the wood tries to differentially expand/contract with moisture changes.

His comparison to apron end-grain joints is irrelevant and specious, because such joints are worse in both respects: First, they're end-grain to long-grain, meaning that the glue's bond strength is greatly reduced. Second, the bonded surfaces have different grain direction, meaning that they build up internal stresses as moisture content changes. A purely glued apron joint is vastly weaker than a purely glued edge joint, and that's why we reinforce them as he describes.

I note with interest that the one thing he doesn't say in the article is that he's actually seen a properly glued edge joint fail. This appears to me to be a case of irrational paranoia.

One thing he didn't go into but that is a valid concern IMO is the longevity of common wood glues (PVA) in particular. As I understand it there are concerns about what happens to those after, say, a century or two. If I were going to be paranoid about edge joints I'd worry about glue selection rather than about mechanical reinforcement.

[Stanley Covington]

A variation on this technique works great for breadboard ends but is totally unnecessary for edge glued boards.

Pat:

I don't mean to be confrontational, but is this just your opinion, or have you tried loose, drawbored tenons for edge-joined boards before? If you have experience using this technique, how did it fail to meet your expectations?

Thanks.

Stan

[brian zawatsky]

This technique works great for breadboard ends but is totally unnecessary for edge glued boards.

I agree. Seems like a lot of totally unnecessary work where a glued joint would more than suffice, although I suppose that would depend upon the application.
In shipbuilding perhaps necessary, in furniture way overkill.
I suppose if one had way too much time on one's hands and wanted to make a simple glued panel joint take 5 times longer and much more difficult, this would be the way to go.

[Patrick Chase]

Lastly, is there any historical evidence of a drawbored, loose tenon tabletop?

More to the point is there historical evidence of glued edge joints failing in significant numbers?

Smart and experienced people do irrational stuff all the time - It's sort of a fundamental trait of humanity, from which all of us suffer in varying ways. Historical evidence of drawbored joints therefore doesn't tell us anything about a rational need to use them (after all, there's historical evidence of the extraordinarily high value of both Dutch Tulips and low-tranche mortgage-backed securities). We'd need to have evidence that the glued sort actually fail to justify that.

[Patrick Chase]

Pat:

I don't mean to be confrontational, but is this just your opinion, or have you tried loose, drawbored tenons for edge-joined boards before? If you have experience using this technique, how did it fail to meet your expectations?

Thanks.

Stan

When you're talking about doing additional work above baseline, "will it work" isn't the relevant question. Of course it will. You don't want to overdo the tension when drawing cross-grain, for the reasons Derek outlined, but other than that it's a well-proven technique.

The question to ask is "does it fix a real problem", and that's where I think Richard's piece is extremely weak.

If you like the decorative aspects then you're using it to fix a different problem (appearance rather than strength) and I would have no qualms about that.