Double top or sandwich top mandola

[WoodyMcKenzie]

I have decided to build a "double topped" mandola after having a very successful experience building a double topped lap dulcimer. I used two layers of sitka spruce veneer with an inner layer of 1/8 inch Nomex honeycomb. I have enough Nomex left over from the sheet I bought from LMI to build a mandola. I have already joined the flat walnut back and will make the sides and neck out of walnut as well.

My intention is to build a top that is arched in one plane by bending thin plywood into a concave form and using that form in my vacuum bag. This instrument might be likened to a flat topped mandolin or guitar family instrument that has an induced arch, but in this case the top can acquire a smooth arch instead of being bent across a brace. If you were building such an instrument, how high would you arch it? Realize that the top is quite stiff, even though the spruce veneers are only 0.050 inches.

I'm also curious to know if any of you have built such instruments. If this is successful, I hope to build CBOMs and maybe a Selmer style guitar this way, if I can find a good source for the honeycomb materials.

Thanks!

Woody

[Graham McDonald]

I would suggest 12-15' radius curve. You can pull a 15' radius braced top in a spherical dome fairly easily with both longitudinal and transverse braces and that might look better than just a transverse curve.

cheers

[WoodyMcKenzie]

Thanks Graham! I have a 15' form that I use for guitar backs, but I was thinking of a more extreme arch that would compare to flat topped mandolins that have the top bent across a lateral brace. I'm guessing that a strongly arched top would be much stiffer and might make for a harder sounding, more projecting instrument. I just wonder how high to go. I have only built two OMs and they are both carved tops with lots of arch so that they look pregnant. I like curves!

Woody

[Graham McDonald]

One idea that occured to me a while back was to mould archtop soundboard for mando family instruments using spruce veneers inside and out and a tapered nomex honeycomb core - thicker in the middle and thinner towards the edges. Someone did suggest that nomex would not be happy trying to form into a dome shape by bending and laminating, and I think I decided it would be entirely too much like hard work http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

I thick a 15' spherical shape would be a stronger and more attractive look than just a transverse arch, but it depends on what the nomex wants to do. Certainly worth trying

Good luck with it

graham

[french guy]

Hey Woody , nice to see you have a project in your bag , good luck , and maybe see you soon . Jean