Top construction & glue up for a split Roubo style bench

[Mike Holbrook]

Sorry to make yet another bench post but...Rather than continuing to to post slightly off topic discussion on other bench posts I hope to target what seems to me to be a major issue in any bench construction. How good the work surface of our bench turns out is the meat of the project and thus far I have not come up with what I consider to be usable combination of materials and top design. I made a couple trips to Lowe's without finding materials I liked. I did a little calling around to lumber suppliers & searching on the net and came up empty that way too.

I have found in other threads on this site and Blogs by posters here that some have used the surface faces of boards to make the two sections of their bench top. Two 2x12 boards with a space between them comes close to the popular 24" bench top size. Apparently a 1 1/2" bench top can be thick enough for work support but fall short when it comes to holding holdfasts. I have read that blocks placed under dog holes to give holdfasts more to make purchase on, frequently split under the pressure. I have read a little about surface gluing 2x12 boards to make a 3" top but I have not found anyone who has actually done this. I am concerned that hand planing two 2x12s to get them flat enough for surface gluing might turn out to be a tough project with a good chance of being a classic fail. Thus far I have not been able to locate construction grade 2x12 boards that I thought would give me a reasonable shot at success. I think the idea of using 4x4 or 6x6 lumber for the glue up is a good one, but I have had even less success locating suitable lumber of this type. All the boards I find seem to be treated & made from the center of small trees. I just purchased 24 4x4 posts for a construction project and the twist etc. in that lumber was even a problem in the construction project.

I made a few calls trying to locate someplace that had soft maple etc. of a size that might work but so far I have not found anything close.

[john brenton]

I wouldn't mind using 1.5" if I were making a Nicholson as there are supports underneath, but not for a ruobo.

I say just bite the bullet and do two 3" laminated slabs. It's a PITA but the stability will be well worth it. In fact, for a Ruobo I would do two 4" thick slabs. It goes faster than you think, and once you see it coming together you get inspired.

[Jeff Schmidt]

Mike,

Clearly, you have thought things out well and have pursued the reasonable alternatives. I agree to stay away from the 4X4's that are centered on the heart of the tree, unless they are very well seasoned and still straight. Also, in my area, all of the SYP is much too wet and usually warps and twists in the drying process. In addition, the resinous rings of SYP are brutal on edged tools.

One suggestion would be to go to various lumber yards and purchase reasonably dry 2X4's (I personally believe a finished top thickness of ~3.25" is more than sufficient), that have one relatively knot-free edge. So as to not have to hand plane the faces of the 2X4's for gluing, you could take them to a local cabinet shop or lumber yard with a planer, or even find a local woodworker with a planer, and ask them what they would charge to run each 2X4 through the planer on each side with as light a cut as possible.

As far as a Nicholson approach, I saw one where the builder screwed and glued a 2X4 to the bottom of each of the two top 2X12's. These 2X4's were located along the two lines where he expected to place his hold fast holes. The 2X4's were let into to the top supports that run front-to-back. (If you would like picture, send me a PM.) The 2X4's stopped at the inside of the front-to-back stretcher at the top of each leg, so they were not visible looking at the end of the top. I do not think that you would need to face plane these before gluing them for that application.

[Mike Holbrook]

John, I have been trying to locate soft maple, ash or some reasonably tough but not to hard to work wood. I think I can find something that is a less expensive than hard maple but better than construction yellow pine. I guess the question then becomes what size to get. I realize rough lumber may not be dimensioned but since I do not have a planer I may need to find something a little less rough. I may try some of the guys with portable saw mills but I think they deal mostly in green lumber, although I think they have or know places that can dry it. Here the issue is how long do I want to wait.

Jeff, I have been thinking about doing something similar to the 2x12 s with a 2x4 glued & screwed to it but I was thinking about one or two 2x6s. I was thinking about ripping two 2x6 boards a little thinner and glueing them to the bottom of the 2/12s, leaving a small gap for wood movement between them. I am not sure if two 2x6s would stabilize the top or just increase the chances of it warping the top piece out of shape?

[Jeff Schmidt]

Mike, on the Nicholson, I don't think that the top is going to be able to warp much since it is my understanding that the top is screwed to the transverse bearing cross supports from below.

[Mike Holbrook]

Jeff, that is a point that is perplexing me. My idea is to build more of a Roubo bench than a Nicholson. The Nicholson has the large apron on the front of the coplanar legs & top. The bench I am thinking about would have a sliding dead man in place of the apron. Benchcrafted has a plan I like for a Split Top Roubo that is sort of like Schwarz's plan but with a split top. I don't think the Benchcrafted or Schwarz Roubos have the same transverse bearing cross supports as the Nicholson designs. The split top obviously needs some additional support but from what I can see of the Benchcrafted top in their pictures, it looks like there are only two supports on either end of the carcass not the seven that I have seen used on Nicholsons with 1.5" tops. I think the supports on the Nicholson designs may be there not only to support the two halves of the top but also the thinner top. I am not sure whether or not extra supports would be needed if the top were 3" thick or more. The Benchcrafted design uses 8/4 Ash.

[Jeff Schmidt]

Mike, you are correct. You do not need the "transverse bearers" with the Roubo-style if you have top >3" thick, unless you were going to build a very long bench. The same applies to the split top. Look at the Charlesworth bench wherein the two slabs are separated by a tool tray. No mid-bench supports. Of course, his is not a long bench but as long as you are staying 8' or under, you will be fine.

You are right, the Nicholson only uses them to support the thinner top and to provide some additional rigidity. Though loads of woodworkers have built stable 6' long benches with 1.5" or 2" thick tops and no transverse bearers.

[Jeff Schmidt]

Mike, On the Nicholson, I would add that the transverse bearers provide some support for the front aprons as well, particularly when one is using holdfasts in the apron.