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Hey y’all I’m Greg and I got an OM kit from Stew-Mac. I have built a semi hollow 12 string from the fret wire and a Les Paul from Stew-Mac that I’m finishing the black lacquer now. I have looked through several pages and haven’t found this topic so I may be stressing over something that’s not important. I got the kit in yesterday and as I’m looking at the top and back they are very rough. I’d say they were sent through a wide belt sander with about 50 grit. Should I bring the inside down to 220 or 320 before I start bracing the top and bottom. Will the rough interior dampen or affect the tone. I have watched the video through the top and bottom glued to the sides and they say nothing about it and the instruction booklet doesn’t either. Thanks for any help.

don't sand past 220 if you sand too fine your finish won't stick.

That's a good question about the sanding the inside. I sand both sides of the top and bottom to 220. Sides too. I don't know if a 50 grit inside surface would effect the sound but I like to have a smooth surface for gluing the bracing and a smooth inside is nice and neat.

Additionally, the smoother surface will trap less dust and make it easier to clean through the soundhole, after the guitar is completed. I don’t know if a dirty interior is a detriment to the sound, but it won’t help any.

I'd be inclined to sand it down so when you look at it your reaction isn't "Somebody should have sanded that."
#180 would probably be quite adequate.

Check your thickness, too. As a general guideline, he top ought to be in the neighborhood of 0.110" thick, the back and sides more like 0.090". Sand one side (the outside) down so it cleans up completely and all roughness is removed, then see how much you need to take off the inside to get the thickness you want.

I sand to 220g, inside and out.

Thanks for the help. I wanted to sand it but wasn’t sure if I should.

Yes - please sand to 220 or 320. Better for gluing and cleanup but also you will see it through the soundhole

Well I have the bracing on the top and bottom and have the top glued onto the sides. Everything has been going pretty smooth so far and no problem other than needing more time to work on it. I sanded top bottom and sides to 220 and it looks good.

Good for you....making progress.
Any pictures?