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To modern eyes, old-school workbenches look like they are going to self-destruct.
The legs are tenoned into the benchtop (which moves with the seasons). And stretchers (that don’t move) are tenoned into the legs. Something has to give, right? Otherwise your benchtop will be cleaved asunder, creating a “split-top Roubo” a la naturel.
I’ve dealt with this issue in several ways.
1. I have ignored the problem. I just glued and drawbored everything up tight on the French-style bench I built in 2005. The result: The legs pivot a bit on the lower stretchers as the top expands and contracts. There are a couple small gaps on the shoulders on the end stretchers. No other problems to report.
2. I altered the mortises in the benchtop. On a couple workbenches I’ve made the mortises in the benchtop that receive the rear legs a little wider. And I didn’t glue the rear legs into the benchtop , I just pegged them in place. The result: The top moves. The base doesn’t. No real problems here either.
3. I’ve bolted the top to the base. This is the modern solution. I used tight holes at the front of the bench and reamed-out holes at the rear. This forces the wood movement to the rear of the bench. When the top moves, it shifts where you don’t see it. The only issue here is I wonder about the long-term lifespan of the hardware.
And now I’m pondering solution No. 4 for the workbench I’m working on now. Here goes: On the end stretchers I’m going to glue them into the front legs, but I’m going to leave the tenons into the rear legs loose.
I was inspired to do this by Roubo’s plates. Last night I was looking over all the A.J. Roubo volumes (yes another high time at the Schwarz household) and noticed that Roubo shows the front stretcher clearly pegged into the legs, but it doesn’t look like the end stretchers are pegged into the legs.
This got me thinking.
The other thing I’m considering is stealing a trick from the Hall Brothers, who built almost all of the Greene and Greene furniture. They made double mortises in some legs. So the tenon and the shoulder are buried in the leg. If I do this little trick, I’ll never have an open shoulder.
Yeah, it’s fussier than is probably necessary. But I’ve wanted an excuse to try these ideas out.
– Christopher Schwarz
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Hi Chris,
I’m going with Item No.1. The Roubo-Schwarz bench that I built a few years ago expands and contracts like an accordian with the seasonal changes here in mid-Wisconsin. Even so, it’s the flattest and most solid surface that I’ve ever done any woodworking on. I built it out of white ash and had fit the tenons into the bottom of the bench top in the middle of May. Didn’t get back to it until a nice humid day in June and could not get the legs out of the mortises for few weeks. The humidity dropped and I was able to wiggle them out. When I had everything fit and ready to assemble I carried the legs and strechers into the a/c in the house for the night. The next morning I could have thrown the things into the mortises from across the garage. Went together quick and was amazed at how solid it was after driving home the last draw bore pin (went with 1/2″ dia to tie the legs to the top). Now a big-time draw bore fan. Also, I had left about a 5/16″ radius in the four corners of each mortises in the bench top, figured it would hurt. Haven’t had any issues, knock on wood. Hey TSJones99, my brother and I built both of our benches at the same time over a 5-6 month time frame and it was a lot of fun. If you don’t have Chris’s book, get it. I probably read the thing a half a dozen times over a couple of years before we made the trip to the sawmill. You’ll really enjoy building and using the bench. Really like the tips and comments noted above.
Kirk
Can’t help but think that the Roubo bench top was cut from a single piece of wood, through the heart of the tree. Essentially making the top quarter sawn. The expansion would be up and down rather than front to back, particularly where the slab meets the tenons. That would put little or no tension on the lower stretchers.
Chris,
Thanx, as always, for helping me decide what to do. I’m in the process (still at it after a year) of building a copy of your Holtzapffel (hope I spelled tht correctly!) bench, and was trying to decide how I wanted to attach the top. With the vise I have I wasn’t sure the down ‘n’ dirty lag bolt method would work, since the top stretcher would interfere with the vise workings, and I’m still a bit unsure of chopping out one inch wide mortises, since I don’t have a powered mortiser. After much gnashing of teeth and rending of garmets I have decided to use your brace-and-bit method, with paring chisels to clean up the walls. Now I have the key to the actual attachment, as you stated in method #2. I’ll make the rear mortises a bit wider and just peg the joint, thereby eliminating any worry of the top bowing or cracking due to movement. Maybe by the time the October WIA comes around I’ll have the bench finished, and can show you pictures of the result. And maybe we can share a draft!
Thanx again,
Stuart Hough
I’ve gone with solution one. I just created blind mortises into the bottom of my bench top and the tenons rest up inside them. I didn’t even peg them or "stretch" them or anything fancy. Because the top is so heavy (approx 140 pounds by itself), it hasn’t moved with anything I’ve tried so far, and I’ve also seen no evidence of cracking. (knocking on big, heavy hunks of wood)
That double tenon does look like a cool technique, if a bit fussy. I’ll be curious to hear how it goes.
Chris,
I love the double tenon. I have been using it recently to attach legs splayed legs to chairs and stools that have an irregularly shaped shoulder. With the shoulder recessed it adds strength to the joint taking loads off of the "small" tenon and it covers over any up cosmetic "angular inaccuracies" that might have stacked up during assembly. This seems like the perfect application.
cheers,
Niels
I use a single 1/2" lag screw through the top of each end stretcher into the bench top. I could have just as effectively used simple dowel pins a la Frank Klausz. Bolts through the bench top and/or multiple fasteners/elongated holes seems like overkill to me.
Also, very interesting interview re "Sawing Basics" on the Lie-Nielsen YouTube channel.
You sir, are a gentleman and a scholar.
and awesome in a truly geeky way. (which is high praise in my book)
Thanks for sharing all your research and thoughts on this, it’s fantastic.
I am beginning to sense that making this bench is not for wusses and/or beginners.
The rule is you need to balance the strength of the tenon and its mortise.
Normally a good balance is to have your tenon thickness equal half of the the thickness of the tenoned piece. So a 5"-thick leg should have about 2-1/2" of tenon thickness. You can distribute this 2-1/2" among two (or more tenons).
Hope this makes sense.
Chris,
Thanks for sharing your three tips to keep benches from exploding. I will remember these along with never putting forks in the microwave.
About the double mortises, what are the requirements on the sizing of the second mortise? I have not read anything on this variation on the mortise in use much so I was wondering if there is general rule to its size.
Thanks
Chris,
This is another of your great postings on the workbench theme. One of the reasons my new bench is going to have a (deliberately) split top is too distribute seasonal movement over two 12" widths rather than one 24" span. I like the idea of a reversible planing stop / tool holder in that gap, ala Jameel’s travel bench. In a knockdown version, as mine will be, dividing the top mass into two parts will make an impending move much easier,as well.
I don’t recall any of your designs utilizing a split top; but I think you mention in your book not liking tool trays and such. If I ultimately don’t like the two piece design, I can join the halves together and add a lamination or two.
Michael Brady