How far do you sand before bending and body assembly?

[cactus bum]

Hi all, My sides and top and back are sanded to 80 grit. I am going to bend sides in a couple of days.
When I make furniture, from maple for instance, I like to raise the grain with water three times or so, sand to 220 before assembly, wax around joints to make cleanup easier, glue up, clean up glue, sand with 220 again and then 320, done. Lutherie is different, I suppose.
How far do you sand sides to before bending? One guitar is mahogany, the other is pao ferro. How far do you sand the outside of the backs? One is mahogany, one pao ferro.
I am especially interested in how far you sand the soundboard before assembly. I don't usually work with spruce and don't want to sand to 220, scratch the soundboard, then have to take more off. I would be especially sorry to sand through the rosette. This guitar building is different in many ways from furniture building, but obviously there are many similarities.
Any opinions are appreciated. Cheers, Cactus

[Hesh1956]

Michael bro this is one of those many things in guitar building where there will be lots of good answers in as much as everyone does what works for them.

Here is what works for me:

Sides:

After thicknessing with 80 grit to .005 more than what I want my final thickness to be I hit them with the ROS with 120 paper to get the 80 grit, drum sander marks out. This is far easier when they are flat. Then I bend the sides.

The insides of the sides will not be sanded again after this. If you look inside of some of the historic and iconic guitars that some folks worship you will see that they didn't even go to 120 grit.

Of course the outside of the sides will get final sanded with 220. Sanding beyond this, depending on what finish that you are using - may - not help with the mechanical adhesion that many finishes benefit from.

Back: Joined at .140 right out of the thickness sander where I use 80 grit again. Once joined it goes back into the thickness sander with 80 grit paper and again I stop about .005 thicker than the final thickness that I want. The next step is to use the ROS with 120 to get the drum sander marks and then I move on to installing the back strip. I am in the minority who installs back strips as one piece prior to bracing.

Tops: Thicknessed with 120 (unless it's a hardwood such as Aussie Blackwood, Koa, Bob Pod, etc. which I have not used on a top - yet). I thickness the top to .140 - .150 and then join it. Once joined I thickness it again with 120 to less than .140ish looking for a clean face with no pitch pockets. Once I have that I install the rosette and thickness the face again but only to take the proud rosette down flush with the top. When I have a clean face with rosette installed all thickness sanding of the top is then done from the back only - don't ask me why..... ^&**&^% pitch pockets!!!!

I used to sand the insides of my boxes to 220 but I don't anymore.

I hope this helps.

[cactus bum]

Thanks Hesh, This really helps. Taking it all down to 120 seems like a reasonable thing to me. I can do that. I guess I am wondering when, if ever, and on what types of wood you would raise the grain with water before sanding. I do this when I want to keep the finish from raising the grain so much.
I have heard the sound is better if one doesn't take the inside of the body beyond 120. Also, I have been told never to coat the inside of the body of a guitar with any finish. Now that I have heard the truth from Heshtone World Headquarters it will become my practice also.
Thanks again Hesh. Cactus

[Allen]

I only drum sand to 80 grit, just a bit more than what I want as final thickness, as Hesh does. Bend, build, bind, then start my final sanding up to 220 - 320. Depends on the wood.

[Nick]

Hesh is right on the money & you won't go wrong by following his methodology. As fars as grain raising goes, personally I raise the grain on all types of timber only if I'm going to stain it. I use waterbased stain on the wood rather than stain in the finish so I don't want furry wood after staining so I'll wet then sand until the grain doesn't raise anymore. If I'm clear finishing I give the wood a wipe over with alcohol prior to putting the first coat on, just to get rid of any waxes, oils and greasy fingerprints that may have found their way on to the wood during building. A quick wipe over with some 120 after this just to get rid of the worst of the fluff then a couple of coats of finish. Then, once there's a base of finish, I'll wipe sand any raised grain. Others will or may do things differently but this is just the way I do it.
As for the inside of the body I always seal it at least. What's the point of sealing the outside surfaces with coats of finish to protect it from climate changes and then leaving bare wood on the inside to absorb humidity? My way of thinking is that you are only asking for the sides or back to split Seal one side of a thin plank and leave the otherside clear and after a while that plank won't be straight.

[Hesh1956]

Sorry Michael I forgot to address the grain raising question.

What our pal Nick said sums it up for me nicely, I only raise grain if I am going to stain so in my case this rarely will mean a neck. In the case of necks I only raise the grain in areas where the end grain shows i.e. the heel area and curves leading to the headstock and the top of the head stock. I think that raising the grain in these areas with three applications of a damp cloth followed when it is dry with sanding makes for a more uniform color once stained.

BTW if you do mix up some stain to say stain a neck be sure to keep some extra labeled and ready in case you sand through during the finishing process. This can be a life saver....

Without meaning to high jack recently I was playing around with egg whites for sizing tops and I noticed that the application of egg white really, really raised the grain and even induced a warp in a top. I repeated the process on scrap (yeah I know the scrap should have been first...) and sure enough the same things happened. Needless to say I was not pleased and don't plan on using egg whites again under French polish.

Something else that you might be interested in Michael if you are into raising grain is baking your tops at 200F for about an hour at least 2 weeks prior to use. After baking the tops feel AND sound when you rub them differently and I would liken it to much like a potato chip feels. The tops have the grain raised a bit and feel very dry to the touch. Although there is much debate over what the benefits, or not..., are of baking tops my own belief is that it stabilizes the resins and pitch to some degree and also slightly changes the molecular patterns of the wood so that they are more resistant to RH changes. I can't prove any of this but so what - I can't even prove who I am some days....

[cactus bum]

Thanks Allen, Nick and Hesh.

Nick, Do you use shellac/sanding sealer for the inside?

Hesh, What color stain do you use for mahogany? I have heard walnut gives a good result. I have never worked with mahogany, at least not to stain. Hesh, do you ever stick a toothpick in the soundboard to see if it is done baking in the oven? My grandma did that.
There really are a thousand ways to do so many things in guitar building, as in general woodworking. It gives us all room to feel what we do is our own. Cheers, Cactus

[Nick]

Yes I usually use a shellac sealer inside the box. The latest build I may use a few coats of danish oil as it really helps accent a curly figure (which is what my inner back is), but the jury is still out on that one. I'll carry out some scrap research first

[Allen]

I use shellac on the insides of all my instruments. 3 coats usually. Enough to seal them up and give them a bit of a gloss. I only and the insides to 180.