Mandola top thicknessing

[sprucetop1]

Just carving the top for a scratchbuilt copy of a Gibson H1 mandola. I'm trying to get the thicknessing similar to oval hole A style mandolins I have already built....i.e. approx. 3mm. minimum in the recurve, centre thickness 4-5mm. with a slight increase in thickness along the string line from tailpiece to fingerboard. The top will hopefully graduate nicely from recurve area to the top centre.

Is this an ok plan for a mandola top of this (oval hole) design, or should the top be slightly thicker? Anyone have any thickness data from an original H1?

thanks.......John

[peter.coombe]

A centre thickness of 4-5mm is way too thin for an oval hole mandola, they need to be built a bit thicker than a mandolin. 4mm is likely to end in disaster. I don't have an original, but I do have one of mine here and it is 6.5mm in the centre, and no thinner than 4mm in the recurve under the tailpiece, rest of the recurve is 3mm. I would not go thinner than 6mm in an oval hole mandola, but the final thickness will depend on the individual piece of Spruce.

[sprucetop1]

Peter.....many thanks for your top thickness information, and I will take your advice. Do you also graduate the mandola backs a little thicker than mandolins ?

John

[Bernie Daniel]

Sounds like you have the information you need. I'll just mention that Roger Siminoff sells an H-4 and H-5 mandola kit. It seems like there might be plenty of information on that topic from his place as well -- his specs would be very similar to Gibson?

[j. condino]

Gibson H1, serial number 61938, FON # 11864 ( approx 1921-1923, depending upon the source you use to date it)

Top thickness: 2.45-3.3mm@ recurve (avg. 2.7), 4.7mm at center just in front of the bridge, 4.2 mm behind bridge.

Back thickness: 2.7-3.1 mm@ recurve, 4.2mm at center , 4.7-4.8mm right around
tailpiece area.

Shallow, flat arches; medium recurve.

oval soundhole= 70mm x 42 mm

ribs= uniform 2.3mm thick, 43mm ( 1 11/16") tall ( ribs only, without top and back).

'Hope that helps!

j.
www.condino.com

www.kaybassrepair.com

coming this month:
www.blueridgeschooloflutherie.com

[draino]

What would be the theory behind needing a thicker top plate for a mandola? String tension should be similar -- maybe even less. I guess the bending moment trying to fold the instrument in half would be greater because of the increased scale length, but the difference seems pretty small -- not sure exactly what the tailpiece-to-tuner distance is on a Gibson style mandola, but shouldn't be that much longer, considering the scale is only ~2" longer.

[Bernie Daniel]

What would be the theory behind needing a thicker top plate for a mandola? String tension should be similar -- maybe even less. I guess the bending moment trying to fold the instrument in half would be greater because of the increased scale length, but the difference seems pretty small -- not sure exactly what the tailpiece-to-tuner distance is on a Gibson style mandola, but shouldn't be that much longer, considering the scale is only ~2" longer.

Little wider across the top along a line with the bridge base too -- this lager expanse seems to be a real problem for mandocellos -- maybe not such a big deal with mandolas?

[fscotte]

Longer span requires thicker wood. Think floor joists - the longer the span, the wider the floor joists are needed.

[draino]

I dunno. The overall string tension on a Gibson-style mandola appears lower than on a mandolin, so it seems like that would counter-balance that slightly increased span. Also, my understanding was that the bigger structural issue for mandolins is the tension trying to fold the instrument in half, not the downward force on the center of the top. A floor joist doesn't experience that kind of force.

[fscotte]

There's quite a bit of downward force on a mandolin bridge, I think around 50 lbs, depending upon many factors. Not sure what the force would be on a mandola bridge, but if it's 50 lbs, and it has a flatter arch, then I'd say it'll need to be thicker. Lots of factors to consider but a floor joist example just shows how making the span longer requires more strength.

[sprucetop1]

THANKS to all for replies.....especially grandcanyonminstrel for the H1 mandola specs. They are exactly what I need. I am not qualified to comment on string tension/loading on a mandola built to an H1 design, but the spruce I am using (European) is, I estimate, on the lightweight side of average so a slightly thicker build is perhaps indicated. I plan to increase the size of the transverse brace (compared with a mandolin brace) as well. However the instrument ends up, it is certainly an interesting project and the more challenging without an original H1 to examine.......John