Knock-Down Roubo Bench

[andy brumenschenkel]

I am in the process of building my bench and have run into a small snag. So far I have the top glued up 25.5" x 84". The original design was to do dual through tenons into the table top for the legs, and pegged tenons for the stretcher-leg connections. This is in a basement shop and the doorway at the top of the stairs is 29", hence why I sized the top width so. I am worried about being able to turn a corner to get it into the hallway to be able to get it upstairs.
Does anyone have any good experience with making the leg-top connection removable?

[Jim Matthews]

Rather than a sliding dovetail joint, consider modifying the connection.

I would suggest a standard tenon, with some sort of mechanical fixture to draw it tight.
This is an excellent question; regarding real-World limitations of stairs, doorways and turning corners with heavy stuff.

Something like this (http://www.rockler.com/product.cfm?page=349&site=ROCKLER) would allow you to snug down the top, and keep it tight with Seasonal changes.

[Wilbur Pan]

My Roubo bench was originally designed with drawbored non-through double mortise and tenon joints to connect the top to the base. Once I got all the double mortise and tenon joints fitted, I realized that the top of a Roubo bench is heavy enough that gravity would hold the thing in place. Three years of use so far, and there are no issues with the connection.

As far as I can tell, the worst case scenario is that I'll have to drawbore the joints at some point in the future. But I'd bet that I won't have to.

[Steve Voigt]

Hey Andy,
I have a Roubo-ish bench, 24 x 88. I used normal rectangular tenons on the ends of the legs, and blind mortises on the underside of the bench.
On the vise side of the bench, the tenons are snug in both directions. On the back side, the tenons are snug from left to right (to help resist racking when planing), but they have over an 1/8" of slop from front to back, to allow for wood movement. It's worked--the top has shrunk, exposing the tops of the legs in back, but the legs in front are still nicely flush with the top. I'm not very aesthetically happy with the shrinkage in back, but at least I know my reasoning was sound.
I also installed upper stretchers between the legs from front to back (but not from left to right) and ran lag bolts up into the top. The clearance holes for the bolts are slotted, again to allow for wood movement. I keep the bolts snug, but not super-tight. I'm not even sure they're necessary, but I can't resist structural overkill.
The only thing I'd do differently is to leave about 3/16"-1/4" overhang in back, to plan for the inevitable shrinkage of the top (inevitable, that is, if you're using home center SYP or similar, which isn't quite dry).
Couple pics below; the second one shows the stretcher to top connection.

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[Andrae Covington]

Does anyone have any good experience with making the leg-top connection removable?

The top of my bench is held in place by two dowels. As Wilbur indicated, gravity will keep the top from flying away.;) All you really need is something to keep it from sliding. I took a circuitous path of methods that included stopped sliding dovetails, but ended up returning to the dowels. I have suggested in a previous thread that the double tenons don't have to be glued, so the top could be pulled off later.

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[Paul Saffold]

My roubo ( http://www.sawmillcreek.org/showthread.php?183190-My-split-top-finished ) is a split top which requires a upper stretcher to support the top. Tenons on the legs into the top are not glued nor draw bored. The weight of the top holds it in place. Each half was about 85 pounds if I remember correctly. A lag screw through the upper stretcher with an elongated hole, towards the inside (away from the leg) allows movement towards the center.

Steve Voigt's method of the oversized mortice on the back of the bench is what I would recommend for a single slab top. I would not recommend dowels in place of tenons. Some have used them without problems but others have found them to be inadequate. They have eventually allowed the top to move under pressure from a vise and the top and leg are no longer flush.
Good luck with your bench. Building one is a great learning experience.
Paul

[andy brumenschenkel]

Thanks for all of the information from past experiences. I had originally thought about continuing with the tenons without glue, but was worried about the racking associated. My plan was to do dual tenons, but I'm thinking that if I need to remove the top that will make it tough. Should I do just a large square tenon, or rectangular. If I do rectangular which direction should they go, long side front to back or side to side?

[Jim Koepke]

My intuition suggest that a rectangular tenon should be in line with the long dimension of the bench.

jtk

[Andrae Covington]

Thanks for all of the information from past experiences. I had originally thought about continuing with the tenons without glue, but was worried about the racking associated. My plan was to do dual tenons, but I'm thinking that if I need to remove the top that will make it tough. Should I do just a large square tenon, or rectangular. If I do rectangular which direction should they go, long side front to back or side to side?


My intuition suggest that a rectangular tenon should be in line with the long dimension of the bench.

jtk

http://d2amilv9vi9flo.cloudfront.net/wp-content/uploads/2010/10/RouboLegDetail.jpg (http://www.popularwoodworking.com/techniques/joinery/a-j-roubos-sliding-dovetail-tenon-joint)

The main purpose for the double tenon, specifically the front sliding dovetail tenon, is to lock the front edge of the bench to the front face of the legs to keep them aligned. When the tenon or dowel or lag screw is set back from the face, even an inch, changes in humidity will cause misalignment sooner or later, as Paul Saffold noted. At times my top has moved back from the leg as much as 1/16". I fussed about it at first, and drilled new dowel holes and planed to realign them. Then they moved again. I gave up. It doesn't keep me awake at night, but if maintaining that planar relationship is important to you, then you probably want to proceed with the sliding dovetail tenons at the front.

[andy brumenschenkel]

I really like the idea of the sliding dovetail tenon, for some reason I'm nervous about the front edge breaking off if that joint isn't glued. Is this justified?

[Andrae Covington]

I really like the idea of the sliding dovetail tenon, for some reason I'm nervous about the front edge breaking off if that joint isn't glued. Is this justified?

Hm, I can see your concern. You didn't say what wood you're using, but I know from experience that douglas-fir is brittle and splintery, my workbench has taken some abuse along the long edges. On the sliding dovetail tenons, I think that once the joints go together, the sharp corners are protected enough that they wouldn't split off, unless you hit them just right with a wayward chisel or something.

[Wilbur Pan]

The main purpose for the double tenon, specifically the front sliding dovetail tenon, is to lock the front edge of the bench to the front face of the legs to keep them aligned. When the tenon or dowel or lag screw is set back from the face, even an inch, changes in humidity will cause misalignment sooner or later, as Paul Saffold noted. At times my top has moved back from the leg as much as 1/16". I fussed about it at first, and drilled new dowel holes and planed to realign them. Then they moved again. I gave up. It doesn't keep me awake at night, but if maintaining that planar relationship is important to you, then you probably want to proceed with the sliding dovetail tenons at the front.

Your experience aside, I wouldn't say that this is a universal issue. The legs of my workbench are attached to the top with double tenons, with the first one set about an inch back from the front face of the leg, and I haven't had the issue with misalignment with seasonal changes that you are describing.

It may be that I oriented the 4x4's that I used for the top so that I essentially have a big quarter sawn slab. It may be that the wood I used is particularly well behaved. But for whatever reason, I don't think that the issue of the front edge of the top moving out of plane with the front face of the leg is a universal one.

[andy brumenschenkel]

Well I have taken a mix match approach. I am going to use single rectangular tenons 1.5 x 4.5, oriented with the length of the top. In order to add some stability over time, I am going to add a single drawbored peg through the front of the bench. This will give me all the strength I need and help with racking. I figured I will have to drill out the peg when it comes time to move it, but I'm liking this option.