Workbench base question (again)

[Michael Hammers]

After thinking about some previous posts on the best way to incorporate the bench leg assembly to the top I am wondering of a better avenue to take. I re-read Chris Schwartz article on the roubo bench because I like the shear mass of the roubo bench. (see this link for what he says about the very subject of movement ect. )

http://www.woodworking-magazine.com/blog/An+Update+On+The+Roubo+Bench.aspx

After studying the Landis book, Sam Allen's book and several years of FWW and Woodworking mags I still am undecided on the base. Chris touts the benefit of the slight A-frame construction of the legs.
Bob Smalser brings some undeniable facts about wood movement and joints though.
So my thought is to just simply build the base with trestle feet and basically a trestle top with which to register the bench top on dowells. In a sense the top would nearly "free float" on the base.
My top is 4 1/4" walnut so the mass itself should take care of the top moving around.
Any thoughts?

[Robert Rozaieski]

Exactly what I did for my bench. The top is 2.5" thick birch and it didn't move even before I added the dowels. I had some of that non-slip drawer liner stuff that looks like the router/sanding mat material between the bench top and top stretchers. The bench top just sat on top of the base that way for months before I actually got around to adding the dowels. Eventually, I removed the non-slip stuff and added a single 1-1/4" dowel in the center of each trestle top and it's held up just fine. I think I drilled about 1" to 1-1/2" into the trestle and the top.

[Hank Knight]

Michael,

My experience is like Robert's. My bench top is 3" thick maple and very heavy. It sits on the base (trestle top) with no mechanical attachment. I planned to attach the top to the base with two clips made of 2" aluminum angle, lag bolted to the base, with one lag bolt each into the center line of the top. But the top hasn't moved in over two years, so I haven't bothered to bolt it down.

Hank

[John Harroun]

Regarding the Roubo style bench of WW magazine, I think the slight A-frame aspect achieved through contraction of the top is over-hyped. Plus, I think its important to keep the bench front (legs, apron, etc.) as square to the top as possible.

Even with a full 1/8" shrinkage on each side, the legs would be only on the order of a quarter of a degree off vertical. With such a slight angle, not many horizontal forces (e.g., forces from an agressive jack planing session) would be projected downward through the legs to the floor.

If an A-frame is desireable, the book Planecraft provides some examples. If I recall correctly, David Charlesworth's bench also has this feature.

IMHO, Christopher Swingley's Roubo style bench design (link below) is a nice one as it avoids the wracking. The top is firmly engaged with the base at the front, but dowels in slotted holes towards the rear of the bench allow for contraction and expansion. This design could easily be scaled up to more beefy proportions.

http://www.frontier.iarc.uaf.edu:8080/~cswingle/woodworking/images/new_workbench.pdf

With regard to the Roubo bench, has anyone here tried those fancy dovetails?? I'd love to hear about how they were accomplished.

A less aggressive design might involve a square through-mortise in the top. Such a mortise could possibly be built after placement of the top (without its front laminations) on the base. The procedure would involve waxing the tenons and shoulders (which extend from the front legs) and adding laminations to the top that snuggly surround the tenons. Laminations would be added until the front of the top is aligned with the front of the legs.