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I want to build a split top Roubo bench. I plan on using Douglas Fir. My question is, would I be better to laminate the top in the usual fashion or would it be better to have a solid chunk of wood that is 4” thick x 12” wide? It would certainly be less work that way. Are there disadvantages to a solid piece like that?
A laminated top should be a bit more stable, especially if the solid top is flatsawn. It's hard to find a rift or quartered piece that large, although it is possible with Doug Fir. With a laminated top, you can take a bunch of flatsawn boards and put them together edge-up, yielding a more or less quartersawn plank. You can also pick and choose the laminates to eliminate knots in the surface, whereas finding a big slab of Doug Fir that is knot-free on one side may be difficult. If you want square dog holes in the top, that is much easier to do with a laminated construction (although you could just laminate a couple of pieces onto the edge of a slab).
It is a lot of work though to prep all of the laminates, and the glue-up is stressful. A solid top looks nice, too.
Larry, I know nothing about Roubos and not much about Douglas Fir but I do know that a single, solid 4"x12" chunk of hardwood wood can warp and sometimes crack with seasonal movement, worse if it's not completely dry inside, less if it is quartersawn. Laminating from thinner pieces allows you to start with dry wood and as each piece supports the others warping is minimized or eliminated. I built a 2x4' table like that from hard maple decades ago and it is still flat. Douglas Fir may behave differently than other species, perhaps it is not a problem, I haven't built things other than structural.Quote:
Originally Posted by Larry Wilson
JKJ
About 4 years back I built my bench from Doug Fir, using some 4 x 6 timbers that were re-purposed. Getting edges and surfaces flat, square and straight (and old finish) took some material off, so I ended up closer to 3-3/8 th x 5-1/4 wd. I only needed 4 of those to make the top wide enough. That greatly reduced both the prep and laminating process. The top has stated very stable since in my garage shop area. Of course those timbers were about 50 years old when they became the top, quite dry. Still, you can readily find 4 x 6 and larger timbers as standard structural timbers, with plenty to pick through to get the type cut, and reduced knots that you want. Consider this variation in the approach.
A Roubo bench has a top that is about 22 inches wide and 6 to 12 feet long, with the most common being 9 feet. The top is a single piece of wood. Roubo recommends beech or elm, pith side up. In the 18th century guys would have thought it odd that anyone would cut the wood up only to glue it back together again.
I had a friend who used a single piece of Douglas Fir that was about 4X18X144 for his bench top. It wasn't new when I first saw it in 1978 and still good when I last saw it around 2010. With a laminated top there is a chance of delamination over time, especially if the bench gets a lot of pounding like mortising and such.
If it were me and I wanted a proper thick Roubo top, with a compromise of ease of work, expense, time, cracking etc., I would go with 4 x 6 on edge so you have 6 boards to buy to get you a top. By the time you plane stuff square and flat, you will be down to about 5". The limited laminations will be easy to glue, but you will get the heft and look more like a single slab. You can also select some better cuts. I have a 'solid' sycamore top that is two pieces, but to do over again, I would have cut it apart and done in 6x6 ish pieces. Ultimately, it is square and stable, but that took a while.