This project represents several firsts for me -
1) First acoustic guitar from scratch. I've replaced tops, backs, bridges, saddles, nuts, done inlay, repairs, etc. but this is the first one from scratch - resawed the wood, bent the sides, etc.
2) First time to do a French polish from the start and not just a repair.
3) First time I've made this many mistakes in a project and kept going, trying to figure out how to successfully fix what I've done and trusting it's still going to work out ok.
So here's the sanding tip I learned a long time ago and I have no idea if it's something I read, something I figured out, or even if it's common knowledge - It takes twice as long sanding with the next grit as you spent sanding the previous grit.
What do I mean by that? If you're sanding a finish, or even bare wood, with say 220 grit and you move to 320 grit, then if you sanded for 5 minutes with 220 then it's going to take 10 minutes of sanding with 320 to remove all of the 220 grit scratches.
Right now I'm wet sanding the guitar that has a very thin film of shellac and when I wet sand with 320 it takes no more than a minute to do the back twice. When I switch to 400 I sand for about 2 minutes although I don't time it. Basically I sand the back twice, wipe the slurry off, blow it dry to see if I have even coverage of sanding, and then switch to 400 and do the same thing. Only now with 400 I do the back about 4 times. When I switch to 500 I'll do it 8-10 times. When I get to 600 I'll be doing it at least 15 times. By the time I get to the 1200/1500/2000 I'll probably keep going until it looks right and then switch to Micromesh.
I haven't made it past 500 yet because I keep seeing where I'm getting too close to burning through to the Mahogany so I've had to stop and shellac again several times. So when I get to the finer grits it's necessary to judge how much finish is left so I don't go through on the polishing later.
Anyway, it's a sanding tip I've passed along to lots of folks so while I'm waiting on shellac to dry it seemed like a good time to post this (only takes a few minutes to dry before I can sand again).