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Thin a top

I built this mandola a few years ago from a nice Cohiba box. Turned out well; the neck is bolted-on and it's held the tension of the full eight strings for several years.

I've started in improving it, however. I've removed the glued-on copper-wire frets and I'm going to install real frets.

I would like to experiment with thinning the top down. It's solid cedar, and about 7mm thick. I do have it cross-braced.
I'd like to take that down to about 4mm to see if the sound improves.

I don't have access to a surface planer... I considered just putting sheets of sandpaper on a glass surface and starting to sand, but that's going to be tedious.

Anyone suggest a more efficient method?

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Permalink Reply by Mark Werner on August 20, 2017 at 5:44am

Good advice. I was considering "scalloping" the braces with my Dremel, but an overall taper might be better.

Right now, I'm doing the frets, when I get those in I'll likely finish up the top and string it up.

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Permalink Reply by Taffy Evans on August 20, 2017 at 12:44pm

Yep I would agree with Ron regarding braces.

If you recall I suggested removing those existing braces and replacing them after thinning the whole top. You mentioned that they are glued with a strong glue, but it is easy to remove them. I would chisel or plane down close to the glue line, then route the glue off with the raised area of timber down to your desired top thickness.

To help with the replacement of the braces maybe a bit of background will help.

Cross braces in an instrument are normally fitted as structural support, and carved down so as to enhance top movement but not lose their supporting strength. In order to support the downward pressure on the top the cross braces should go all the way to the sides, and are glued to them. In order to give the top the ability to vibrate/flex the braces are thinned strategically at their the ends.

An important part of cross braces is the joint where the two arms cross, this has to be tight.

I have shown two of a few different styles of bracing I have used, the small top area means less braces are needed and they can be light. Both these styles produced great sounding instruments. I have since gone lighter on both styles.

The bracing subject is far more involved than can be covered here, and involves many other factors that must be considered.

Mark I would suggest, if I may, that you could do a great experiment by tapping the top close to your ear, hanging between thumb and finger, I would expect it to sound dead with not much ring to it. Redo the bracing as mentioned and as you carve them tap and listen, that response will change, should come livelier and more musical. Sorry to ramble on.

Cheers Taff

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Permalink Reply by Kigar on August 20, 2017 at 3:19pm

Hi Taffy,

In both pictures you added a layer of material around the sound holes, can you enlighten us as to the reason? Cosmetic, structural or ? Thanks

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Permalink Reply by Taffy Evans on August 20, 2017 at 4:12pm

Hi, as the tops are solid cedar, not ply, and about 2.5mm thick that is a very fragile area so I reinforce the top with a very thin venneer cross grain to the top.
Taff

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Permalink Reply by Mark Werner on August 20, 2017 at 11:38pm

Remember, in this case I'm dealing with the tension of a full set of 8 strings on this instrument.
I'm erring on the side of sturdiness! This mandola is several years old, and it's shown no sign of the bolt-on neck loosening or of any collapse with the existing top, which is about 7mm thick.
Sound has always been at best, adequate.

I'm a bit afraid of pushing the boundaries on this one, so I plan to reduce the top to a total of around 3-4mm, and just thin and taper the existing bracing.
Easy enough to disassemble at some point if I want further experimentation.