Structural Overkill? (EUB related, copied here)

[ii7-V7]

I'm going to begin building an EUB once I get a few more components. Right now I'm in the planning and drawing stage. The design that I'm going with is similar to, but not a copy of, the bespoke basses with the two long pieces of wood running perpendicular to where the top would be. These connect the neck to the endpiece. The bridge will press on these two supports. Check out the photos of Bespoke Basses at http://www.bespokebasses.co.uk

I'd like to keep to weight as low as I can while still maintaining structural integrity. The question is can I get away with using two 1"x4" pieces of Poplar? Would I have to go thicker, or should I go with a stronger wood such as maple? I'd like to avoid overkill and I think that two pieces of Poplar bearing the weight across its short face should be plenty strong enough.

Chad

[Francois Blais]

I'm copying this thread in the Setup & Repair forum where there are several luthiers lurking.

[Thor]

I would be concerned about the side to side flex of the
poplar. Particularly in the area shown where is it drilled out
just below the end of the fretboard.

That being said, the Bespoke has at least 4 manual attachment
points that I can see, as well as a fairly large
block at the endpiece. Also, the 'wings' that the bridge
sits on add to the structural rigidity of the side piece.

The quickest way to test this is to take 2 pieces of poplar,
drill the 4 holes, insert a dummy block at either end and see if
the test assembly is rigid enough to appear to perform satisfactorily.

FYI Poplar (yellow) has a density of 30 lbs per cu ft.
Maple has a density varying from 35-44 lbs per cu ft.
(Source: Pocket Reference from Abbeon Inc. )
Both are listed as a medium hard wood. But apparently the
maple will be 20-50% heavier.

The stuff is really not so expensive thay you can't afford to
test it out. Worst outcome is that you have to switch
to maple. I would fabricate it just enough to do the test
without investing time in any other aspect. Once I was
decided on that, then I would move ahead.

[ii7-V7]

Well I wasnt going to drill the holes in the side like the Bespoke bass. I also will have a larger support area at the bridge. Looking at those basses gives me confidence that what I'm designing will work.

I like your suggestion of trying a test with with Poplar. You're right poplar is cheap enough that if it fails I will have learned something and I won't be out much money. Any idea just how much pressure the strings put on the bridge? Would hanging the appropriate amount of weight be a fair test.

Chad

[Thor]

I have no idea how much force is exerted. Someone like Ken Smith may be able to tell you that. I suppose if you took a
hanging scale and saw how much weight was required to
pull a D or A string off the bridge and multiplied that by 4, you could approximate the weight required.

However, since that force is exerted from 'side to side' of the
piece of poplar, I would not be overly concerned about
movement in that direction. I would be more concerned about
stability from 'face to face' of each structural piece, for lack of a better term.