View Full Version : flat top mandolin cave in
I own a Godin A8 E-acoustic mandolin with flat top.
The top ist not really caved in - but also not exactly flat.
When I put a ruler along the top (from neck to tailpiece) it is about 1 mm / 0.04 inches caved in at the bridge.
Is that a normal value for a flat top mandolin?
Thanks
GEH
What type of strings are you using? A friend of mine has a flatiron flat-top and it specified fairly light gauge strings.
.010, .013, .024, .036 (like Martin M400 strings)
One thing about flat tops is that almost all of the support comes from the bracing. I built a stewmac army-navy style kit last fall and used medium strings (j74) which coupled with overly carved bracing resulted in ~2mm of sag. I ended up taking the top off and replacing the main lateral brace with a more substantial piece of spruce.. The old brace was warped into a concave shape from the heavy load. With the new brace it its holding up fine but I only use light gauge strings now as well. Hope this helps, Keith
Luthier
Jun-03-2004, 7:55am
I use a pre-carved arch bracing in my flat tops. #If you have a round or oval hole on the mandolin it may be possible to glue another brace in. #It is a lot of work to remove the top but that is also another alternative. #Can you post a picture??
Don
Sorry... what is a pre-carved arch bracing?
1 mm ist not a big cave.
You only see the cave when you hold the Mandolin flat in front of your eyes.
Maybe a flat top ist always a little bit caved - or not?
This is my main question.
Luthier
Jun-03-2004, 10:51am
I'm sorry for not explaining this better. #My fault. #Picture the back of an accoustic guitar. #It is arched and not perfectly flat. #In order to achieve this concave shape on the outside, the braces inside must be shaped with that arch or curvature. #In the flat top kits that I make, I put the arch in the brace by routing it with that shape, hence the term pre carved arch bracing. #There is always some deflection on the top from the string pressure on the bridge. #It may be very negligible but it is there. The "beefier" the bracing, the less caving in but you then sacrifice sound.
Don
From my limited experiences with both flat tops that a couple of friends own (flatiron and weber y2k) neither had any noticable sag which made me think my version 1 bracing on the kit mando was doomed to ultimately fail. It was very loud with the lighter bracing but now is just moderately loud with a little cleaner tone (less harsh). BTW (Don) the new brace is taller and thinner than the original and both were made a slight arch when installed.
I guess the point I was trying to make is to check that the strings are not heavier than recommended for that model of instrument. Good luck, Keith
PS: Don - I going to try one of your kits next time I build a flattop http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif