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So what's the thinking ..very smooth or fairly rough inside the guitar..also smooth or rougher for glueing braces. Anybody?

Can you explain your question a bit more?


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Wondering if I sand the inside and braces with 1600 grit and get it lovely and smooth wether this improves sound or should it be rougher to excite the soundboard more..

Also does glue bond better on super smooth or slightly rougher surfaces

If it matters at all, the difference is very small. Do whatever's easiest/most fun for you.

For me, that's plane/scrape the plate, carve the braces with chisel and finger plane, and call it done. Less dust that way.

I'll go along with that. I finish the inside with a very sharp scraper. There's more than enough dust in all the other processes.

Haha fair enough maybe I'm overthinking it.. Can't help thinking even if it's a very small difference it could be worth the dust

What do you guys think about glueing smooth or rougher for best adhesion

I go up to 220 on the drum sander...

You deffanatly want smooth glue surfaces. The joint should be as much wood to wood contact as possible.

I use a Cabinet scraper to dress the glue surfaces just prior to gluing.

Some people sand the surface, Not sure if it really matters, but I will choose a scraper over sandpaper every time since I don't like to create any more dust than I have to.

Besides scrapers just have a much more tactile feel and sound than sandpaper

Bob

Cheers bob .. Your probably right the titebond seems to stick like a bad memory ..prob overthinking it all

I sand to 150. Going to 1600 might bea good selling point though!

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Pat

I believe in smooth surfaces overall and smooth glue surfaces, too, but the best way to achieve the glue surfaces is a sharp scraper. Then you have freshly cut wood as a gluing surface. As for everything else inside the soundbox, I make it as smooth as I can with sandpaper, scrapers, etc. Sweep and vacuum out all the dust. Dust and debris (and perhaps even a spider nest) will eventually accumulate inside a guitar, but I believe that funky stuff is less likely to stick and settle onto a smooth surface. Benedetto goes so far as to shellac and then lightly sand the interiors of his boxes (after his braces are mounted), but I think he is somewhat outside the norm when he does that. Very many people here look a long way forward to the day when they might have to re-glue a brace or whatever. They don't want anything like shellac or other finishing materials on their potential glue surfaces. My personal opinion is that old glue would need to be cleaned off anyway, so the surface is already contaminated with old glue and there would be no shellac in the gluing area to worry about, anyway. If it's not contaminated with old glue, it's probably contaminated with oxidation and dust. I'm just saying most old guitar interiors would need to be cleaned up before repairs could be made--even if you were cleating a crack. I'm not telling you to finish your interior. But I am telling you I think you ought to make it smooth.

I think you'll get several follow-on responses now saying: "DON'T FINISH YOUR INTERIOR". Remember, I did NOT advise you to finish your interior. Just make it smooth.

I always seal the inside surfaces of my mandolins and my archtops with shellac. As Benedetto says "the sealer is needed to help prevent a sudden absorption or loss of moisture" . It is a little effort but well worth the trouble.

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http://www.cushmanguitars.com/.

A man who carries a cat by the tail learns something he can learn in no other way.
Mark Twain

Years ago Sergei de Jonge wrote an article for Guitarmaker, it was fall 1999. In it he talks about the effect of how smooth or rough the interior surfaces are on the tone of an instrument. He says that Patt Lister did an experiment where he could modify the interior surfaces after the guitar was strung. When the interior was smooth and lacquered it sounded too brash, very trebly with no warmth. When rough it was too bassy. Sergei says "If I want a guitar to sound brighter I make the inside surfaces a bit smoother. If I want more warmth I leave them less smooth" He prefers 150-180 grit for a classical and 100 grit for a steel string. He also says that he used to scrape the inside surfaces but he prefers the less brash tone of a sanded surface.

Aside from aesthetic issues, why do you think it would matter? I'm assuming you must have some premise or you wouldn't be considering it.

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Jim Watts
http://jameswattsguitars.com

Someone's has been smoking the drapes again and not sharing....

Maybe it's time to take a guitar and do some blind listening tests....

Choice A could be the guitar as is and choice B could be what it sounds like after being strapped in a paint shaker with 1,000 single edged razor blades in the box....

It may be that no one could tell a difference but it sure would be fun to watch the thing implode in the paint shaker... Anyone want to donate one of theirs for the experiment?

Seriously so you mean that informal competition that I have been having with Lance all of these years to see who is more anal about sanding and smoothing inside the box has been a boon to our trebles and a bust for our bass????

Really seriously I know some folks finish inside the box. I'm not keen to do this being a repair guy too because I doubt that interior finish slows the ravages of RH swings much at all AND in terms of serviceability if someone has to reglue a brace someday or cleat a crack they are going to have to be removing finish inside the box with limited access physically, etc.

Also and this has been discussed before if you look at some of the iconic instruments it's not uncommon to see saw marks, rough surfaces, etc. inside the box. It worked for them!

It's been said here before what whom ever decided that guitars have to be smooth and shiny should be dug up and shot. If you guys start finishing the insides too we will just have to dig up that guy again and shoot him twice...

I think 1600 is a bit over the top. I just scrape mine. I cannot for the life of me think of any mechanism that would cause a rough inside to be more bass and a smooth inside to be more treble.

Archtops are different in that they have but 2 braces on the top. Flattops are a repairmans dream. Neck resets, loose braces and lifted bridges. Archtops don't often need these repairs so sealing the inner surfaces is unlikely to affect a repair. Sealing the inside protects the glue joints from moisture. This is a good thing when using HHG. I also seal all my flattops and some of them are over 15 years old now and I haven't had 1 loose brace or any cracks so far. The braces don't have sealer under them only over them. I have built more than 50 so far without any repair other than a stripped truss rod. As far as iconic instruments I think those built by Bob Benedetto qualify. Bottom line is anytime there is a problem that needs repair you will probably be the one doing it. So do what YOU think is best. I think any difference in sound is very minimal. I know most builders don't seal the inside so we know it is not necessary.

_________________
http://www.cushmanguitars.com/.

A man who carries a cat by the tail learns something he can learn in no other way.
Mark Twain

And I was hoping that someone would pass some of those drapes my way...

We see over 1,100 instruments in our shop annually and every single one of them was made by someone who is not fixing it themselves.... Of coruse this includes hobbyist instruments (danger Will Robinson...) to some of the biggest names in the biz. So I don't agree that because we make em it's a given that we will be fixing them. Stuff happens and there are a lot of geezers in the trade too, I know.... I am one....

I'll always be singing the praises of servicability because, well.... it's my nature.... I don't see any real harm in finishing inside the box beyond what I mentioned above and the need to remove finish if any repairs are needed. No biggie.

But I do dispute the notion that a couple coats of shellac is going to prevent damage from drying out. RH by it's very nature permeates surfaces and although finishing the inside may slow the process I can't see the slowing being more than a couple of hours max.

Also no biggie and I'm always the one to advocate thate folks do exactly what they wish. Just thought though that some would find it interesting that servicability is a worthy criteria to consider in how and what we build - always.

Lastly - we see some instruments that the maker has finished the insides too. It never looks good to me, the inside finish, and can and at times does look rather amaturish IMO. Maybe it's time to market a robotic micro-buffer-drone that we can set free inside our boxes to buff em all out....

We have a kind of sort of pre-war Martin, very nearly pre-civil-war that is (Eric.... ) in here for a complete restoration. Looking inside the thing is pretty interesting at least to me. If anything smoother than 120 was ever used on this one it's fooling me... The hand work is beautiful though especially the ice cream cone neck heel and the slots for the tuners. Those guys were skilled and it shows.

No finish on the inside though and let's see by my count this one has made it about 140 years now and soon will be good to go for another 30 or so.

Ideally a perfectly smooth surface is best for a good glue bond. The old idea of roughing up is surface to key the glue in was mistaken. However, if you smooth to the point of burnishing the wood cells closed - either with a dull scraper, plane etc, the glue will not be great either. Sanding to about 220 works well for me, and most folks I think.

AFA the sound, I agree 100% with Sergei DeJonge. There actually is a surprising difference in reflectivity depending on how finely a wood surface is sanded (or finished). It's enough that an audible difference would be expected. I saw some data on this 10 or 15 years ago that opened my eyes. It's not going to change how much a soundboard is "excited", but it will change the degree to which high frequency sound is absorbed or reflected before bouncing out the soundhole.

Subjective A/B tests would IMHO be a waste of time, and lead to arguments. If anyone is really curious, it would be reasonably easy to devise a reflectivity test with a prepared wooden board using basic audio test gear.

Thanks for the replys..will probably sand with 220 then glue...would expect the back bracing to be the most responsive to sanding as it deflects the sound out to the soundhole.. that said the braces must act like baffles even if there super smooth ..so cant imagine a brash sound from an un lacquered interior

Ahhh what have i started here still none the wiser.

As mainly a builder of F holed instruments, I know I won't be doing any repair by reaching in the box, as my hands are too large to fit in. If there is a problem inside the box it would have to be opened up to do any kind of work so it is less of an issue for an f holed instrument.

_________________
http://www.cushmanguitars.com/.

A man who carries a cat by the tail learns something he can learn in no other way.
Mark Twain

Really? That is not what many luthiers think how a guitar works.

Ok barry new to building..perhaps you can educate me

I'd say you're speculating about chimera. As a new builder you're probably better off focusing your attention on the foundations of how guitars do what they do. I suggest you get the Gore/Gilet books. They are very technical, but very very instructive.