Soundboard too thin?

[colburge]

Hi all,

I have embarked on my first attempt at building my first acoustic using Cumpiano's book and already made a miscalculation regarding the top thickness. I meant to take it down to 120 thou as per the book but it ended up more like 90-100 thou. I wasn't concentrating, and was thinking 120 thou was 2mm even though I knew it was 3mm. I didn't take it all the way down to 2mm, as I wanted to leave my self some room to move, that's why it's around 2.5mm

I know Cumpiano's book says that it is probably too thin for a steel string, so I didn't want to proceed any further with it, if it was just going to cup and fail when strung up. Do you guys think I would be better of starting over with a new top or should I try to beef up the bracing, or just leave it?

I think you would say it is a medium size guitar that I am building as I am not sure on sizing as I drew it free hand per the book, and the soundboard is an inexpensive piece of AA 1/4 sitka.

Thanks

Col

[kiwigeo]

Welcome to the forum Col,

0.120-0.125" is about what I aim for around the bridge area on my steel strings but thickness towards the perimeter of the outer bout decreases and can get down to 0.090" with some tops. Final thickness is governed by each individual top and how it feels and taps as I'm working it down.

On my classicals where I've used sitka I've worked the tops down as thin as 0.080" but there's a bit of leeway for going thinner on a classical due to lower string tension.

On your steel string it's very hard to advise you without having the top in my hands and being able to ascertain how stiff it is and what sort of tap tone its giving. From my experience the bracing as per Campiano's specs is a bit on the beefy side......you may be ok just going with the bracing as is and get away with it. I would consider adding an extra brace along the back of the bridge plate for a bit of extra insurance. If the top is so thin it feels floppy like thin cardboard when you flex it then a new top may be the go. The old top can be used for soundhole patches, back reinforcement etc.

The above is based on my experiences. Others in here will no doubt chime in and their advise may differ from mine.

[Paul Eisenbrey]

The soundboard on my second guitar was also very thin. Right around 2mm over most of it, and very floppy: I had my calipers gapped incorrectly, and failed to double-check . I salvaged it by re-enforcing the soundhole area and putting an extra brace right behind the bridge patch. It worked out pretty well -- the guitar sounds fine.

Of course, wood being wood, your mileage my vary...

Good luck!

--Paul

[Allen]

Really depends on the woods stiffness as to whether it's too thin, to thick, or just right. But only experience will teach you that.

If you are worried about it, then put it aside and save it for a smaller bodied guitar or even a baritone ukulele.

[colburge]

Thanks guys

I may as well leave it and put an extra brace on it as Martin suggests, it is a learning experience after all - if it fails, it fails, and I wont do it again. Ideally I should feel a soundboard that is thicknessed correctly, that way I would know what it should feel like if I ever build another.

Thanks guys, I am going out to the shed now to route a slot for my truss rod and have a beer.

Cheers

Col

[Allen]

Kent Everett has an excellent dvd that shows thicknessing a top using a wobble test to get to that point where you're ready for bracing. Well, the dvd covers a lot more than that. And I highly recommend it for everyones library.

I've used it to great effect on guitars. It is simply running the top through the drum sander and after each pass giving the top the wobble test. It's surprising how just the tinniest bit coming off in thickness all of a sudden takes a top from a board, to something almost musical.....you've got a lot more work ahead of you yet, but it did make a difference in getting that feel on how stiff each board was, and the difference in thickness, even in the same packet of tops.

[Nick]

Kent Everett has an excellent dvd that shows thicknessing a top using a wobble test to get to that point where you're ready for bracing. Well, the dvd covers a lot more than that. And I highly recommend it for everyones library.

I've used it to great effect on guitars. It is simply running the top through the drum sander and after each pass giving the top the wobble test. It's surprising how just the tinniest bit coming off in thickness all of a sudden takes a top from a board, to something almost musical.....you've got a lot more work ahead of you yet, but it did make a difference in getting that feel on how stiff each board was, and the difference in thickness, even in the same packet of tops.

Welcome to the forum Col
I'd second Allens comments about Kent's DVD and all my steel strings get the wobble test as well as flexing to get a feel for how the top wants to move. The Selmer Maccaferri's I build use a 2mm thick soundboard and are ladder braced (a more 'open' style of bracing) and stand up to a string pull of a 670mm scale really well. Admittedly the tops have a three dimensional 'barrel' shape so that gives the top an extra bit of built in strength.
If this was a number "x" build then I'd say use the top and beef up the X bracing height to compensate, but seeing as it's your first and you aren't yet sure about what you are feeling when flexing and taping the top whilst carving the braces, I'm tempted to say put it back into your stash to use a bit further down the line when you have a bit more experience to know what you are looking at. That's how I would do it but somebody like Trevor or Dominic, or anybody that uses Trevor's system, may be able to tell you how to approach using this top now, more confidently by using mathematics and getting the numbers to tell you how it's going to behave or do what you want.

[jeffhigh]

I'm not going to tell you whether to use it or not, but things to consider would be
-How much more will be removed in finish sanding
-how much time and money do you have invested in this top vs total time and money to finish the guitar

[Phil Mailloux]

I'll +1 the Kent Everett DVD too, its been invaluable for making the top on my first acoustic, most of the AA Sitka Spruce (from Stewmac) is around the 2.5mm mark with nearer to 2mm around the edges, I'll let you know how it went when I string it up first but so far with the bracing this thing feels structurally sound.

[colburge]

I'm not going to tell you whether to use it or not, but things to consider would be
-How much more will be removed in finish sanding
-how much time and money do you have invested in this top vs total time and money to finish the guitar

Bugger it, I will just order another top, I want to get it right. I don't want to invest a crazy amount of time building a guitar and have it sound terrible or the soundboard buckle, down the track, it will just p*ss me off. It wasn't an expensive top, but I did spend a bit of time making and installing a rosette which is disappointing.

I think I will go for a higher quality soundboard this time around, now that I have practised joining, and installing the rosette, I am confident I can get it right. I might try and find a local supplier here in Brisbane this time and choose it myself, but I am not sure if there is one, so I might have to wait for the postman again.

Kent Everett has an excellent dvd that shows thicknessing a top using a wobble test to get to that point where you're ready for bracing. Well, the dvd covers a lot more than that. And I highly recommend it for everyones library.

I've used it to great effect on guitars. It is simply running the top through the drum sander and after each pass giving the top the wobble test. It's surprising how just the tinniest bit coming off in thickness all of a sudden takes a top from a board, to something almost musical.....you've got a lot more work ahead of you yet, but it did make a difference in getting that feel on how stiff each board was, and the difference in thickness, even in the same packet of tops.

Welcome to the forum Col
I'd second Allens comments about Kent's DVD and all my steel strings get the wobble test as well as flexing to get a feel for how the top wants to move. The Selmer Maccaferri's I build use a 2mm thick soundboard and are ladder braced (a more 'open' style of bracing) and stand up to a string pull of a 670mm scale really well. Admittedly the tops have a three dimensional 'barrel' shape so that gives the top an extra bit of built in strength.
If this was a number "x" build then I'd say use the top and beef up the X bracing height to compensate, but seeing as it's your first and you aren't yet sure about what you are feeling when flexing and taping the top whilst carving the braces, I'm tempted to say put it back into your stash to use a bit further down the line when you have a bit more experience to know what you are looking at. That's how I would do it but somebody like Trevor or Dominic, or anybody that uses Trevor's system, may be able to tell you how to approach using this top now, more confidently by using mathematics and getting the numbers to tell you how it's going to behave or do what you want.

Thanks, the DVD might be something I look at if I decide to build more guitars down the track, along with other books.

Cheers

Col

[Lillian]

Col, I understand you not being comfortable with the top and wanting to go with something you trust Just don't toss the top. There's nothing really wrong with it. And who knows what you'll want to do in a few months. You might decide to make another guitar, maybe a smaller bodied guitar. Maybe an OO.

[kiwinoz62]

Col,
Get the Kent Everett DVD (Re: my post The Gallery #2 Completed) you won't be disappointed.
I learnt the hard way.