Hollow EUB top thickness: Don't need a crack

DavidRN · #1 02-04-2007, 09:08 AM

Hi, been awhile since I have been able to visit the idea of building my EUB. I have decided to go with a hollow body for the upright sound. I still have that Bubinga plank. I thought about hollowing a piece of maple and then using the Bubinga on top and back, about 3/8 of an inch thick, for a real contrast. anyway, I am not planning to carve the top and see no real reason to given the smaller size of the Eub and the Barbara bridge I will be using.

My question is, how thick should the top be before I run into the thought of cracking?

I am also thinking of using spruce and maple if the Bubinga doesn't work. This is probably how I will wind up as I am looking for spruce planks now.

The Messenger starts out as 1 inch thick spruce before carving, I have no idea what the final thickness is.

I do know that the carving of the curve is what gives the top its strength. Just need to know how thick, or thin I can go before I would need to worry about it cracking.

Thanks for the input.

jsbarber · #2 02-04-2007, 09:35 AM

I have an Azola Acoustic Bug Bass, which is hollow (hence the "Acoustic" in the product name). The top is spruce and the ribs and back are ash, if I remember correctly. This instrument has a much more authentic DB sound than the solid body version, IMO. I would suggest you stick to spruce for the top, since that is almost universally what is used for this purpose on not only basses, but cellos, violins, violas..

The thickness of the top will depend on the size/shape of the top plate, and how it is supported. e.g., Are you using a bass bar and sound post?

Hopefully some of the luthiers on the forum will contribute and give you better direction.

Jim

DavidRN · #3 02-05-2007, 10:16 AM

Actually, I hadn't really planned on having to support it at all.
I know the Eminence has a bass bar and post, but, I am not sure about the Messenger. I did speak with John over there, about a year ago, and he didn't relay that he used a bar or post. I got the assumption that he just has a hollow area under the bridge with no support and uses the strength of the 1 inch spruce that he carves handle the load. Not entirly sure on that though.

jsbarber · #4 02-05-2007, 02:07 PM

My Azola has an arched top and is nowhere near 1" thick. It is about 1/4" thick, if that. Not sure if Steve used a soundpost or not.

Jim

DavidRN · #5 02-06-2007, 06:46 AM

I think I figured out how I am going to do it. I am going to do a double top like some of the guitar luthiers are doing now with the NOMEX insert. 76% stronger than just the wood. with 3% less weight.

I have also seen that some guitar makers love bubinga for the sides and back. I may try to do a franot with it too just to see if it will work.