Workbench Question

[Cody Cantrell]

I am in the middle of a build right now and have a question? Failure to prepare right? I am building a Roubo bench and am not sure how I should attatch the top. Is there a benefit to the sliding dovetail and Tenon combo versus a drawbored mortise and tenon joint? In Schwarz Workbench books he builds two different versions one with the DT Tenon and the other with a 2 1/2" x 5" drawbored tenon. I have watched a video with David Charlesworth and he says if you have the leg penetrating the top it will only be flat in that area at certain times of the year. As far as ease of construction goes the draw bored tenon seems to be the way to go but thought I would get some other opinions first. Thanks for any suggestions.

[ken hatch]

I am in the middle of a build right now and have a question? Failure to prepare right? I am building a Roubo bench and am not sure how I should attatch the top. Is there a benefit to the sliding dovetail and Tenon combo versus a drawbored mortise and tenon joint? In Schwarz Workbench books he builds two different versions one with the DT Tenon and the other with a 2 1/2" x 5" drawbored tenon. I have watched a video with David Charlesworth and he says if you have the leg penetrating the top it will only be flat in that area at certain times of the year. As far as ease of construction goes the draw bored tenon seems to be the way to go but thought I would get some other opinions first. Thanks for any suggestions.

Cody,

Other than to show your joint making skills or lack thereof there is no structural advantage to the sliding dovetail/tenon and as David Charlesworth pointed out there may be some disadvantages. I've built several workbenches with housed and pinned tenons, one is over 40 years old, and there has never been a problem with stability or strength with any of them. It's a workbench, not furniture. Build it fast, build it simple, heavy, strong and cheap, then go to work making furniture. Of course I must add as with all things wood....YMMV.

ken

[Jim Ritter]

Another consideration is the vise. If you have a leg vise than the dovetail tenon is "best" because the forces of the vise bear on the leg directly and can't shift the top. I still built mine with draw bored mortise and tenon but with a really beafy tenon to resist that pressure. I have twin leg vises on the bench and everything is as square today as when I built it. I think both will work just fine if understand the forces on the bench. If you hang a metal vise then it really doesn't matter in my mind.
jim

[Cody Cantrell]

Jim that is what I was concerned with I will be using a leg vise. The tenon is pretty beefy but it would be pressing against top not the leg.

Ken I feel up to the task it is just not sure if the sliding DT is worth the effort. I probably wont be keeping this bench for myself.

[mike holden]

I am going to suggest that you may NOT want to use the through dovetail/tenon.
I did that, and am NOT happy with it. The top is flat only about two weeks a year; one week in the spring and one in the fall. The rest of the time it is either proud or sunken. Otherwise, I love my bench.

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[Joel Thomas Runyan]

I built mine with through dovetails and tenons--top is 5 inches of yellow pine. The tenons do alternately sink and stand proud with the seasons, but this has affected me absolutely not at all--and I prep all my stock by hand. There just hasn't been a situation in which I found them *really* interfering with my work. However, I make absolutely no effort to keep my bench pretty in the course of regular things, so if the tenons are too proud I take a whole minute to plane them down knowing that the top will catch back up next time I clean/flatten it, which is about once a year anyway. It is far and away the more difficult of the two joints to execute, but has an absolutely ridiculous amount of strength. I don't think a circus elephant could've made my bench rack with the legs alone, much less before I put the stretchers on.

[Phil Stone]

If you are building your Roubo with large legs and associated tenons, there is plenty of holding power for the top, even under pressure from the leg vise. I didn't even drawbore my top to the legs; it is held on by gravity, and plenty of it -- it doesn't move. I wouldn't worry about the leg vise pressing on the top. It won't make it slide if the front leg m & t joint is nice and tight (you can actually build a little slop into the rear joints, to allow for seasonal top movement). I really don't see what advantage the through dovetail tenon brings, other than a nice piece of visible craftsmanship.

[John Sanford]

There is an excellent video out there of a gent gluing up the leg with the tenons incorporated in the glue up, which means that "cutting" the tenon is as simple as cutting the various pieces to the appropriate length before glue up. Obviously not a simple option if you're fortunate enough to have honkin' timbers to work with. One thing to keep in mind is you CAN drawbore the sliding dovetail if you want.

[Warren Mickley]

The Roubo benches are designed so that they can be easily dismantled. All of the pinned joints are accessible from the back so the pin can be knocked back out very easily. A pinned tenon going into the top would have no backside access and would have to be drilled out. One would have to be careful not to mess up the offset of the holes.

Roubo shows three different leg to top joints; none are pinned. First he has a through dovetail and tenon, second a dovetailed tenon going to about an inch from the top (and possibly a tenon as well), and third a hidden tenon. Diderot and Moxon both show a single through tenon for each leg. So there are some historic choices. I would be surprised to see a pinned top joint in historical work.

I have used a bench with through dovetail for all stock preparation since 1979. The seasonal variation has not been a problem. Considering the quality of work Roubo was producing and the care he used to document it, the through tenons must not have been a problem for him either.

[Phil Stone]

The Roubo benches are designed so that they can be easily dismantled. All of the pinned joints are accessible from the back so the pin can be knocked back out very easily. A pinned tenon going into the top would have no backside access and would have to be drilled out. One would have to be careful not to mess up the offset of the holes.

Roubo shows three different leg to top joints; none are pinned. First he has a through dovetail and tenon, second a dovetailed tenon going to about an inch from the top (and possibly a tenon as well), and third a hidden tenon. Diderot and Moxon both show a single through tenon for each leg. So there are some historic choices. I would be surprised to see a pinned top joint in historical work.

I have used a bench with through dovetail for all stock preparation since 1979. The seasonal variation has not been a problem. Considering the quality of work Roubo was producing and the care he used to document it, the through tenons must not have been a problem for him either.


Warren, the beauty of the joint aside, how does a through-dovetail hold the top any more securely than a (non-through, regular) mortise and tenon?

[Warren Mickley]

As I mentioned there were several configurations in historic texts, so analysis is complicated. But keep in mind that with these benches, the top is not sitting on a rigid frame as in later benches; the top is part of the frame. Short tenons will keep the top in place but will not help in rigidity. The longer the tenons, the more leverage (longer moment arm) there is to resist racking. And more surface area for the tenon to work against. A five inch tenon will perform better than a three or four inch tenon.

There are also some considerations with regard to ease of construction. In general it is easier to make a through tenon, working half way from both sides, than a deep hidden tenon. And generally easier to make a through tenon accurately because it can be laid out nicely on both sides which tends to correct for the errors in making deep tenons. A tighter mortise makes for strength.

The subject is complicated, but I hope this gives some ideas.

[Joe A Faulkner]

Technically, my bench is not a Roubo, but has similar features. I used simple mortises in the top, aligning the legs flush with the top. I also have upper stretchers between the front and back legs and ran a lag bolt to keep the bench top snug to the frame. The top is not pinned to the legs, and can be removed by removing a couple of lag bolts.

[Barry Dima]

There is an excellent video out there of a gent gluing up the leg with the tenons incorporated in the glue up, which means that "cutting" the tenon is as simple as cutting the various pieces to the appropriate length before glue up. Obviously not a simple option if you're fortunate enough to have honkin' timbers to work with. One thing to keep in mind is you CAN drawbore the sliding dovetail if you want.

This one with David Barron?


https://youtu.be/cBPxhIjJy7o?t=2m48s

Either way, watching people describe laminations for joints reminds me to listen to smarter people—and tempts me away from practicing M&T as much as I should.

[Pat Barry]

Someday you may want to move the bench to another place, perhaps a new home, perhaps pass it down to someone in your family. I therefore think you should consider a lift off top and forget making any fancy locking sliding dovetail joints. Otherwise, just try and move a fully assembled bench of this type - bring lots of friends. I used a drop on solution with blind mortises and tenons on the top of the legs. It can be removed easily enough but its tight enough so as not to move around while I am working on it. I suppose I could have pinned it somehow but it really hasn't been necessary.

[Brian Holcombe]

Having just made a very similar group of tenons for my bed frame I can attest they are very strong and lock tightly. I'm curious if the historical ones included even a minor taper to them? I made a pretty heavy taper in mine to aide in fitting.

5" tall sliding dovetails combined with 5" through tenons will make for a very sturdy joint. If this bench is ever to move, and everything eventually gets moved....then make it to take apart.

[John Sanford]

This one with David Barron?


https://youtu.be/cBPxhIjJy7o?t=2m48s

Either way, watching people describe laminations for joints reminds me to listen to smarter people—and tempts me away from practicing M&T as much as I should.

Yup, that's the one.

[Curt Putnam]

Warren and anybody else - does the calculus change for split top benches?

[Warren Mickley]

I have not paid much attention to the split top benches, but it seems that there would be crosswise rails at the top of the legs that are important structural parts. However you would still need tenons into the top to resist racking in the long direction of the top. altogether a lot more work.

The thing about the 18th century benches is that they are simple to make. You get nine pieces of timber, make 12 joints and you have a sturdy bench. Although Roubo liked his double tenons, it seems from other sources that most of these benches had a single tenon at each joint. I think Roubo would have laughed at David Barron's design: a lot of extra work to avoid sawing tenons and making mortises.

Here is a plate from Diderot showing a bench with a single tenon through the top at each leg.
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[Paul Saffold]

Split top benches have an upper stretcher. Mine has a blind M&T, 1.5" deep, to join the leg to the top and a lag in an over sized hole to join the top to the stretcher. Any moisture related movement of the top is towards the center opening. My lag is from the underside of the stretcher. I have a leg vise and have not any problem with the top remaining flush with the leg. The M&T is not glued or pegged. I have taken the bench apart and reassembled it easily, which is a big advantage of this style.

Paul