benchtop wood expansion question

[C Carruth]

My benchtop is glued up oak flooring, set vertically so the edges face up. I am attached a 8/4 apron all the way around, using sunken carriage bolts to secure versus glue. I have looked at a lot of solutions, but most assume you do not have the top enclosed within another frame. Securing only one side or only the middle of the edge to breadboard end does't seem to be an option.

Question: How do I allow for expasion of the core table top in this scenario, or should I not worry about, given the individual slats are only about 1" thick by 2.5" wide?

[Anthony Diodati]

[Stephen M]

Respectfully... No. The cell of a tree is like a toothpick. When hydrated, it will swell in girth but not length. If the bench is oriented North/South it will expand and contract both east/west and up/down.

To answer the original poster: Don't attach the apron pieces to each other, and lap them (no miter). That is let them just slide past one another. Glue the front and back aprons; bolt the sides. Install one bolt tightly on each end cap. Other bolts should have a sloppy hole to allow movement.

Imperical data: I have gotten through almost 1 full year with a 3"x24" lamidated maple top. Casual inspection show about 1/8" (at the most) in the

24" dimmenson summer to winter. With the tight bolt centered, that's

[Anthony Diodati]

vertically,

North/South

[Stephen M]

Proportionally, I think it's about the same. That is a 1x6 will expand more in width, just because it's 6 and not 1.

As an asside, people here have suggested that that quatersawn boards are more stable. That's a bit misleading. Since interior parts of a tree are generally more dense than the newer growth, this will cause uneven changes in two sides of a board, resullting in cupping of a flatsawn board.

By contrast, a q/s board will expand and contract as much as a flat sawn board, but it will do so (more) evenly with respect to both surfaces, and will be less likely to cup. It will still expand and contract with humidity changes.

-Steve

[jev]

Wood expansion/contraction is measured in 3 directions -

0 Radial ie. sort of across growth rings along radisu from center of tree as for example across quarter sawn board o tangential to the growth rings as for example across a flat sawn board o longitudinal - along the grain

Greatest movement occurs tangentially with the radial movement generally on the order of 30-50% of tangential and almost negligible(fro most cases) along the length.

So, as indicated below, movement across the workbench top cannot be ignored.

If you are >I see what you mean, I thought it expanded more in width, than in thickness,

[Stephen M]

(obviously) I did not know about the radial vs. tangential difference.

Good Info!

Thanks,

Steve

[C Carruth]

That sounds good, except I was hoping to do a nice dovetail or boxjoint on the front corners of the apron. Would it work to do the front with dovetails, and leave the back joints simply buted without glue, allowing for the movement you indicated? I would bolt the front aprons, attach the breadboards as you described, and the back as I indicated? Would that work? Thanks.

Chris

[Stephen M]

Yes. You can only lock the end cap to the top at one point. If that's the front corner, that's fine.