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I am flying blind on this one. Helping a friend put together a mandolin that he started twenty years ago. His workmanship is very good but his book/plans do not include top thickness. I do not want to spoil his good work by making the top too thick or too thin. If I have a range, I can help him to produce a decent sounding instrument on a long-delayed project.

My best guess is 90-100 thou.

Any help would be appreciated.

Bob

I'm not pretending to be an knowledgable , I've only built three, but my tops were .110ish Sitka. One perfectly flat, and two with a very slight radius, ladder bracing on all three.

They are all tolerable for tone, but need a firm strum to produce volume, and then they sound kind of harsh. I think I would go thinner if I did one again.

Ray:
Thank you for the comment.
It makes my 90 to 100 thou a reasonable number if a tad thin.
He is using ladder bracing and will likely glue it in my go-bar deck using 25 or 15 foot dish.
I may recommend a 1/16" maple bridge patch for safety.

Bob

The tops on my flattop mandolins are 3mm thick. I use European or Engelmenn Spruce, or King Billy Pine tops.They are X braced with carbon fibre reinforcement and are radiused with a 15ft radius. Bracing is more important than thickness because it is the braces that provide just about all the structural strength. Just an X is not sufficient, mine are braced similar to a guitar, but without the tonebars and with additional bracing under the tailpiece tp stop the top folding in under the tailpiece. The X and the cross brace are carbon fibre reinforced. There is no bridge patch. Flattop mandolins have a nasty tendancy to fold in around the soundhole, so the challenge is to have the thing strong enough so it won't fold up, but at the same time to be flexible enough to sound good. Experience has shown me my system works. The mandolins are stable, they stay in tune, there is hardly any sinkage in the top when the strings are installed, and they sound great. Not as refined sounding as my carved top mandolins, but are noticably louder and with huge ring and sustain, and most important sound clean, unlike a lot of other flattop mandolins. You can play them real loud with no loss of sound quality. People seem to like them. They are fun to make and play.

Do you have a pic of your bracing?

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Doug

Don't let fear or common sense stop you from trying to build something

I have finally seen the book that he is building it from. The book calls for 3/32 (94 thou, 2.38 mm). They use an X brace with three tone-bars and two side braces. There are two transverse braces, above and below the sound-hole.

We have sanded the sound-board to 95 thou.
This week's project is to profile the neck and prepare the Spanish heel.

Thank you for the help.

Bob

I have only made one mandolin it was a flat top with a fixed bridge (no tailpiece) so the forces on the top are different. I has an x brace and one tone bar (neither of which I would call beefy). I'll have to measure the top thickness bit it is likely around 0.1 - 0.12". It is holding up to string tension just fine.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Picture and more info here -

http://www.anzlf.com/viewtopic.php?f=1&t=4932

I have now made about a dozen of these mandolins, and around 150 carved top mandolins.

I intended to measure the soundboard thickness on my flat top (mentioned above) but I can't fit my calipers in the little sound hole without taking all the strings off. I did find a picture of the bracing. Remember this is a glued pinless bridge not a floating bridge with a tailpiece. The bridge plate is very thin and light. The braces are just less than 1/4 inch wide and 1/2 inch tall at the X and taper down fro there. The top is domed to whatever dome I use for guitar tops (I have never measured my dish in terms of ft radius but it is based on the deflected arch recommended in C&N). Once strung, the soundboard did rise in the bridge are, but not my much. The geometry worked out pretty much as I planned which was good because I was flying by the seat of my pants, and wasn't 100% sure I was bracing it well enough. . .



Here you can see that bridge belling was not really an issue.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Mandolins with a fixed bridge are a completely different animal. The forces on the top are quite different, and they will sound different. Mandolins usually have a floating bridge and a tailpiece, so the force on the bridge is a downwards force only. The tailpiece has a rotating force from the pull of the strings. A fixed bridge mandolin, however, like a guitar has a rotating force on the bridge, and there is no tailpiece. The bracing and thickness of the top need to reflect these differences so if your mandolin has a floating bridge, a fixed bridge design is of not much help. The bracing of a floating bridge mandolin needs to resist the tendancy of the bridge to sink into the top, and also to resist the tendancy of the tailpiece to rotate into the top. These are the most common failure points of a mandolin top. Either the top sinks, or the top breaks or bends under the tailpiece. On the other hand, a fixed bridge mandolin or guitar top will tend to sink in front of the bridge and bulge upwards behind the bridge.

Thank you for the details. Your help has been really useful. This is not an ukulele and eight steel strings makes me nervous.
I would feel safe using Bryan's bracing pattern using a 1/16" maple bridge patch and a wide tail-block with a tailpiece. The sides and back are plenty thick.

Bob