Popular Post difalkner Posted June 13, 2018 Popular Post Report Share Posted June 13, 2018 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). Wet sanding Fresh shellac David 5 Quote Link to comment Share on other sites More sharing options...
wdwerker Posted June 14, 2018 Report Share Posted June 14, 2018 I haven't heard it stated that way before but it is definitely true. Skipping a grit is not a good idea. It take 6 to 8 times longer to remove the scratches when you skip a grit. I charge 35-40 % more for a high gloss finish because every tiny flaw turns into a obvious crater ! It always takes far more finish, time and abrasives to achieve an acceptable appearance. 2 Quote Link to comment Share on other sites More sharing options...
Coop Posted June 14, 2018 Report Share Posted June 14, 2018 I’ve always done what I saw and read and used the pencil lines and when they were removed, I considered myself done. And in doing so, each progressive grit usually takes me half the time of the previous. Now you’re telling me I need to spend twice the time behind that exciting dust producer? I shall play like I never read this. 2 Quote Link to comment Share on other sites More sharing options...
wtnhighlander Posted June 14, 2018 Report Share Posted June 14, 2018 I'm with Ken, at least in regards to sanding bare wood. Each successivly finer grit seems to take a little less time than the previous grit. Maybe the reverse is true for sanding a finish? Quote Link to comment Share on other sites More sharing options...
difalkner Posted June 14, 2018 Author Report Share Posted June 14, 2018 I think it depends on the finish you'll be using and the type of wood. Successive passes with finer grits do take less than the coarser grit but it's the only surefire way I know to remove the scratches left by the coarser grit. When I do the Walnut trophies, for instance, and shoot them with clear Nitro I can see scratches if all I did was sand with 120 and give a token pass with 150 or 180 grit. But when I step through the grits 120/150/220 on bare wood I almost don't need to do anything with the finish except spray it on and let it dry. And it must make a difference because the trophy shop I do these for always comments on the finish being better than anything else they get from other guys who do work for them. David 1 Quote Link to comment Share on other sites More sharing options...
wtnhighlander Posted June 14, 2018 Report Share Posted June 14, 2018 Interesting. My observation is that when using the pencil line method to determine when the full surface has been sanded, the lines disappear a little more quicky as I step up to higher grits. But I usually start at a lower grit (80, most often), especially on panel glue ups, to be sure any joint irregulaities are smoothed out. Quote Link to comment Share on other sites More sharing options...
Brendon_t Posted June 14, 2018 Report Share Posted June 14, 2018 9 hours ago, K Cooper said: I’ve always done what I saw and read and used the pencil lines and when they were removed, I considered myself done. And in doing so, each progressive grit usually takes me half the time of the previous. Now you’re telling me I need to spend twice the time behind that exciting dust producer? I shall play like I never read this. Well I think we already already pressured a Domino in your shop. Why not add a CT Vac and 6" ec ? The missus wouldn't mind.. Quote Link to comment Share on other sites More sharing options...
Coop Posted June 14, 2018 Report Share Posted June 14, 2018 I'd like to think that but the truth is, she wouldn't know! I would probably disguise it as garage door repair or something similar. Quote Link to comment Share on other sites More sharing options...
wdwerker Posted June 14, 2018 Report Share Posted June 14, 2018 You already have the CT vac Coop. A ETS 150 sander really is an excellent way to sand. The 3mm orbit does super fine prep for finishing. The 5mm orbit version cuts a little faster but can leave barely visible fish hook lines. With finer grit paper I can't see them with my ETS150/5. I've got both sanders & 2 vacs to speed up all the sanding before we can finish a job. Sorry for the high jack, we return you to your regularly scheduled program, back to Davids high gloss guitar ! 2 Quote Link to comment Share on other sites More sharing options...
difalkner Posted June 14, 2018 Author Report Share Posted June 14, 2018 No problem on the high jack! LOL! Now I'm going back out to the high gloss guitar... David Quote Link to comment Share on other sites More sharing options...
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