Thickness of woods for top, sides and back

[Pablo]

Hi to you all.
I've just started working on my first project. I have a few doubts regarding to the thickness of the woods that are used for the top, sides and back. To be more precise, I'm interested on HOW you reach the desired thickness.
First of all, I must say that I don't have a plane sander. I've seen that most luthiers use it for this purpose, but unfortunately I must think of other options right now.
1) The woods I bought are about 3,5mm (.140 inch) thick. I'm planning to sand them down using a hand held sander and a little help of a belt sander. But I'm afraid of ending up with an uneven thicknes troughout the board. I have a thickness indicator I could use to rectify this. But, it can be quite hard to sand every board using that technique (even though I'm willing to).
2) Other option, is to pass them through the planer (obviously, taped over a thicker piece of wood) The thing is that I don't really trust my beloved woods to the jaws of that machine (even though it's blades were sharpened lately). Maybe the blades are a little misaligned and the wood would come out uneven. And being such a thin wood, it could chip out and ruin it. I dont' know. Maybe I'm being over-protective. I would like your oppinion on this.
3) Sand them by hand.
I must claryfy that both the top and the back halves have already been glued together and passing them trough the planer is not an option now (due to it's with). I've already started sanding them by hand. Nevertheless, I'm interested on your oppinion for further proyects. Plus, I still haven't set hands on the sides (and I'm seriously considering passing them trough the planer).
I would like to know aswell how fanatic (as we say here) should I be regarding this issue. I know that the with of the boards (particularily of the top) makes good part of the sound profile of the instrument. But maybe I'm being a little obsessive...
Thanks for your help!

Pablo.

[tippie53]

If you don't have a thickness sander you can use a hand plane or a hand scraper, A hand belt sander may get you close , you just need to be careful
Side thickness .085 to .095
top .110
back .110 to .100 depending on species. Stiffer the thinner

[B. Howard]

I do all mine with a #3 Baily bench plane. I have it set up as a mild Jack plane. It's quick efficient and QUIET. Doesn't polute my lungs and shop with dust, nothing but curls to sweep up when I'm done. It's a little more physical work but honestly doesn't take any longer than the multiple passes through a thickness sander to do the same. Do not try and do it with a thickness planer, the wood will most likely shatter and become very pretty toothpicks.

[Pablo]

Just clarifying John's post: stiffness is a function of thickness (cubed, if you want to mathematical). If you want a piece to be LESS stiff, make it thinner; MORE stiff, leave it thicker.

A small change in thickness can translate into a big change in stiffness! In my building, the thickness/stiffness of the soundboard is the single most important variable in determining the tone of an instrument. Because of the importance of this relationship, most luthiers use the most precise method they can beg, borrow, buy, or rent to thickness the plates. While luthiers historically planed to thickness, for us (untrained, unskilled) it's better to use a thickness sander.

A hand-held belt sander is not a substitute!

Thanks for the explanation!
Just for the record, I do not have a hand-held belt sander.
I don't know how it is called in English, but is a Makita square-section vibrating little sander (I think you call them "for finishings").
Plus, I do have a belt sander, but it is not hand-held.
Nevertheless, I get the idea. I'll see what comes out...
Thank you

[Pablo]

I do all mine with a #3 Baily bench plane. I have it set up as a mild Jack plane. It's quick efficient and QUIET. Doesn't polute my lungs and shop with dust, nothing but curls to sweep up when I'm done. It's a little more physical work but honestly doesn't take any longer than the multiple passes through a thickness sander to do the same. Do not try and do it with a thickness planer, the wood will most likely shatter and become very pretty toothpicks.

I'm interested. I have the same plane.
Anyway I'm worried about the same thing: keeping it even (I guess it's a matter of experience -which I do not have-). How do you know when you've reached the desired thickness? Do you use a dial indicator or some kind of instrument? Or you just do it by eye?
PD: I'll take your advice on the thickness planer. Thanks!

[tippie53]

I think my thickness sander is faster than a plane but I agree , there is a satisfaction in learning to use one. Also it is musical to hear the shearing of the curl off the wood. Be sure that it is well sharpened and set up. A skill well worth learning.

[Kevin Sjostrand]

Hi Pablo,
I know that little sander is slow, but you can accomplish the task with it. I did 4 guitars that way. On the back and side wood use 60 grit to start and work up to about 120 until you are at your desired thickness. Just check it regularly with your calipers and you can keep it quite even, plenty good enough. On the top wood I would start with 80 grit and work it up.
Just stay at it. I have spent a couple of hours doing mine in the past. It can be enjoyable, just dream of how your guitar will look when it is all done while you are sanding, and it will be over in no time.

Kevin

[B. Howard]

I take a few measurements at first, but once I've I establish how much I am planing off with each pass it's just a matter of calculating how many passes I need to take. And yes John your sander is most likely quicker, especially on the plates. But it is still way louder and dirtier and it goes pretty quick with a well tuned and sharpened plane once you find the rhythm of the work.