Deflection Tuning

[mandomaniac]

Hey Folks,
Wonder if anyone has any followup on the deflection tuning jig ? There was a discussion some time back and Scott even reposted some pics. I was definitely taken by this approach....and would love to see what results are out there now. It seems like FrenchGuy had one 'up and running'....not sure who else.....anything to report that might help the rest of us?? Seems like a great way to put a top 'in the ballpark' and then fine tune from there. The consistency 'top to top' that it seems to offer was what struck me. Any info on your experiences would be appreciated!!!! Thanks....Tom

[Michael Lewis]

There is an article in American Lutherie about the mandolin making class Don McRostie taught at the American School of Lutherie in Healdsburg. There is a good photo of Don's deflection stress set up. It is different than the one in the previous Cafe thread in that it adds pressure to the top with a lever, not strings.

[french guy]

Indeed, I tested clearance on a top by reproducing a tool similar to that of mandoluthier1. this mando has been string up in the white for last Thursday and I must say that I find it very powerful.( the most powerful that I 've never built) . but I also changed other thing which must, each one, to influence this change. in particular, I built an ebony bridge nonadjustable and lighter than the traditional Gibson brige, (10 gr., for the mine instead of 15 gr. gibson model). I had as noticed as on the very first mandoline that I built, the direction of the wood of the tonebars was horizontal whereas the known plans recommend a vertical wood direction, I think that the horizontal direction gives sufficient rigidity but more flexibility and thus perhaps a better attack, but I am not a specialist on the matter, just a point of view. This mandoline is a form C instead of F5 thus there is less of wood in the design. the truss rod is out of carbon fibre Plus of lightness. ON THE WHOLE this mandoline weighs 850 grams whereas my 4 preceding constructions weigh 950 grams. Therefore, to summarize, much parameters evolved/moved. I think for the next one, if however I launch out in the construction of next, I would assemble neck, rim and top together, and I would make a system which will compensate the absence of the bottom, in this way I would have the exact position of the strings and the exact pressure of the strings on the top what will have to make it possible to approach the balance of the top in a more precise way.
All I've to do now is meet mando player around me for having their opinions and compare with others mandos.
For resuming , I will never build a mando without using this process now .

[mandomaniac]

FrenchGuy.....can you share the deflection of the top when under full tension of strings? Or if you have used a given weight, I can calculate at least an approximation to compare to. My jig tests top under full tension...all strings tuned. Using break angle and total of string tensions, downward pressure can be determmined. Thanks...

[french guy]

Mandomaniac,
Yes I've used the full tension of strings , strings tuned .
I've installed two calipers on the bridge and start to tighten the strings , then the top move down . I think it was
due to the edge not tonebars for the moment.
The move down was about 1 mm . If your top is more stiff maybe the caliper don't react.
Then begin to work slowly on the two tonebars with gouges.
Personnaly , I have stopped the working when , during the work , the calipers begin to react again . So I think that if you use the same break angle , the same strings guauge , you will have a top in balance between its own force and the force exerted by the strings.
Hope it can help .