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Two quick questions:

1. How close do you thickness your top on a thickness sander to the final thickness to consider final sanding? Specifically, if you are shooting for a finished instrument with a top to 2.1mm at the thickest, how thin would you go with 120 grit on the thickness sander?

2. How fine do you sand the inside of your tops?

Thanks,
Chuck

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Chuck Kish

Assuming my rosette is in, I thickness sand with 180 to within .005 of the target on my drum sander and block sand with 220 inside and out before bracing. Then I sand with 320 after the binding and purfling lines are scraped before finishing.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

Chuck;
Final thickness should not be determined till the top is on the guitar.
Otherwise your making a factory guitar.
Of course you do want to make a too thick(stiff) or thin top(loose).
Start with a set goal and LISTEN to the top as you flex & tap it.
Then when it's a guitar WITH binding you can voice(thin)
The top.
Mostly on the edges!
Hey were close !
Let's get together and talk shop!
Mike

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Mike Collins

I can't agree that final thickness should not be determined until the top is on the guitar. Some people do it that way but it's not the only or necessarily the best way. Thicknessing earlier certainly does not mean that you're building a factory guitar.

I do completely agree that tapping and flexing and listening to the top is crucial at all phases of construction. Making a pretty top is secondary to making a responsive, good sounding one.

Thanks for the input. With more experience, this will all be more routine. I am looking for a general idea at this point. To complicate things, I am building a Selmer style and about to bend the pliage. If the top were flat, it would be easier to thin later. The plans I have show the thickest part at 2.1mm. I have thickness sanded to about 2.5mm now.

Looking for a ballpark rough pre-assembly thickness at this point.

Hi Mike, I have been wanting to contact you for some time. Spoke with your wife at the Woodstock show -- sorry I missed you there. Would love to pay you a visit. I'll PM you.

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Chuck Kish

I know im a newbie , but 2.1 mm seems to thin to me , is that REALLY the standard we should be shooting for on a top ?

I am working on one right now and my rough thickness is 4mm , I look at 2.1 mm and think that looks like paper to me .

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The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
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Well Wud; 4mm is thicker than I have ever gone at assembly. (I'm one of those guys that do some final tuning by sanding the top after assembly.)
.125" is about as thick as I go, as a starting point before assembling the box. That'd be for a larger guitar or a not very stiff top. Depending of stiffness & instrument size, I go as low as .095". Sorry, I still don't speak metric...

LOL Actually i dont speak metric either , .125 was what I was aiming for as finished thickness . Is that to thick ? I am doing a Mini Jumbo basically .

_________________
The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

2.1mm sounds quite thin to me as well, but possible depending on the piece and the skill of the builder. I certainly wouldn't expect a plan to suggest going that low.

I'm only on #3 (all standard X braced), but I've been working around .110-.120" rough thickness so far (looks like that's around 2.8-3.0mm). Stiff enough to tolerate a little noob stupidity in brace carving, but thin enough that it has some good flex before bracing. The one I just strung up a week or so ago sounds quite good, around .120". The bracing is very light, so it's good evidence to me that stiffness of the soundboard as a whole is more important than stiffness of the unbraced plate. But I plan to start pushing it thinner as I build more and get a better feel for flexing braced plates.

I finish with a scraper on the inside. Nice smooth surface for gluing, and no need to worry about what it looks like (corduroy effect versus raised grain lines). Same for rough outside, then final sand to 320. Hard to judge exactly how much the final sanding will take off... especially if it gets dented at all after the rough thicknessing, and needs things steamed out and then sanded smooth. Another reason for staying on the thick side, until I learn all the ways that dents happen
I think ideally I would leave less than .005 for final sanding (that's a pretty big difference when you get below .090), but I'm not sure if I'll ever get THAT good at protecting them.

Of course doing some final voicing after binding is allowed too, but I'd rather not plan on taking much off at that point, since I can't easily judge how thin it's getting other than by sound... which doesn't tell me so much about structure.

I thickness sand with 80 grit. Subsequent sanding takes off about .25-.3 mm unless I'm trying to thin more.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

I too go 80 grit on the drum sander until it feels right / sounds right. Although this guitar will mark my first foray into flex testing and data. I'm so excited to get to combine two of my favorite things, Excel and guitar building.

There is some additional thinning that occurs cleaning it up by hand, and I assume that varies, but I haven't measured it. For consistency, I suppose I ought to get some higher grits for the drum sander, but I haven't.

And as to final thickness, my first guitar, due to Operator error, has a top that is mostly 1.5-1.75 mm, and as thin as 1 mm in the upper bout. It's been 3-4 years now and so far it hasn't ripped apart. It's got a belly and I'm scared to put on anything heavier than 0.011s, but it's got a sweet tone.

If I ever figure out who that guy "Operator" is, he's getting fired. He sure screws up a lot of stuff around here.

Mike

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Mike Lindstrom

Mike , I think he's moonlighting here as well .

_________________
The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

So Howard, with that in mind, do you assemble the box with the parts thickness sanded to 80 grit, or do you prep fine sand each part before assembly?