High gloss sanding tip - Woodworking Talk - Woodworkers Forum
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post #1 of 11 Old 06-13-2018, 05:00 PM Thread Starter
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High gloss sanding tip

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
High gloss sanding tip-001-wet-sanding-back-french-polish.jpg

High gloss sanding tip-002-wet-sanding-back-french-polish.jpg

Fresh shellac
High gloss sanding tip-003-french-polish-back.jpg

David

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post #2 of 11 Old 06-13-2018, 10:34 PM
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Thanks for the sanding tip. And, congratulations on having the patience and knowledge to know when you’re about to sand through before you sand through.

How about some more pics of that guitar?!? It looks great. I’d be interested to learn more about your build. How did you bend the sides? Hot pipe? Heat Blankets? Other?
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post #3 of 11 Old 06-13-2018, 11:39 PM Thread Starter
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Thanks! Sometimes I have more patience than knowledge. Come to think of it, if my knowledge was greater I wouldn't need the patience so much.

I purposely have not posted much on the build because it's taken a while and I didn't want it dragging out. The sides were bent with a heat blanket and a fixture of my design. You can see part of it on my YouTube channel header. I bent the binding on a hot pipe for the cutaway and headstock and on the fixture with heat blanket for the body. Also bent the lining, which is solid and not kerfed, on the fixture. One of these days I'll post more on the build.

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post #4 of 11 Old 06-13-2018, 11:57 PM
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Thanks, David for a wonderful post. I also would like to see more photos. It seems I have been sanding all wrong. There is a lot more to sanding the way you do it. You must love sanding. I may never sand again.

Don in Murfreesboro, TN.
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post #5 of 11 Old 06-14-2018, 12:28 AM
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Sanding with 220 or 320 grit would be alright for between the coats sanding but not the final coat. It just takes too much sanding to get the scratches out. I wouldn't sand the final coat with anything coarser than 1200 grit.

A french polish is just an application method developed before anyone ever thought about spraying a finish. It just doesn't make any sense to do a french polish finish when sprayers are cheap and easily available. Just spray the finish sanding between coats. Spray the final finish and most of the time you can call it done. If rubbing is desired, sand it with 2000 grit paper, buff it and it look great.
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post #6 of 11 Old 06-14-2018, 01:05 AM Thread Starter
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Nah, takes all the romance and fun out of doing the hand rubbed finish, becoming one with the finish and the guitar and all that stuff, Steve.

David
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post #7 of 11 Old 06-14-2018, 11:58 AM Thread Starter
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Quote:
Originally Posted by Steve Neul View Post
Sanding with 220 or 320 grit would be alright for between the coats sanding but not the final coat. It just takes too much sanding to get the scratches out. I wouldn't sand the final coat with anything coarser than 1200 grit.

A french polish is just an application method developed before anyone ever thought about spraying a finish. It just doesn't make any sense to do a french polish finish when sprayers are cheap and easily available. Just spray the finish sanding between coats. Spray the final finish and most of the time you can call it done. If rubbing is desired, sand it with 2000 grit paper, buff it and it look great.
All joking aside, Steve, it is very different than just spraying the shellac on the guitar. By rubbing I can introduce pumice and wood dust to fill the pores as I am padding the surface. You can't do that when you spray. You could sand the shellac and let the dust fill the pores but I have a feeling it wouldn't be quite the same. You could rub the sanding dust and pumice into the pores after you spray but if that's the case then spraying just wastes shellac with the airborne material so I might as well just do the French polish.

I agree with you that it would definitely speed up the process but this has been nice. No fans going, no open windows, just simply rub the shellac on and wait a few minutes to sand or apply another coat. And yes, it would probably look great if I did as you said and I may do the next one that way, but I wanted to do one start to finish the old fashioned and time honored way of a traditional French polish.

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post #8 of 11 Old 06-14-2018, 09:39 PM
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You're suppose to do all the filling before you apply the finish. If it's an open pore wood you use a pastewood grain filler first. Then if you miss a spot you can dab some shellac on the spot and let the shellac fill the void.

If the fans are a problem shellac dries quick enough you could do it outdoors. I do most of the finishing work I do outdoors. Sometimes if I'm spraying enamel I will do it indoors at the end of the day and leave the building until morning.
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post #9 of 11 Old 06-14-2018, 10:08 PM Thread Starter
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Filing the pores before finishing is an option but the traditional French polish finish incudes filling the pores with the shellac, pumice, and optionally wood dust as you're rubbing the pad on the surface. I chose to fill the pores by that method because I didn't want to introduce a synthetic paste filler. The guitar body is Honduras Mahogany so that's the dust I used. The pores filled very quickly and it looks natural.

The fans aren't a problem. I was referring to when I spray lacquer and having to open windows and turn on the exhaust fan. It's just nice and quiet with nothing but the radio and the subtle sound of the pad on the guitar. I could get used to this if it paid anything - LOL!

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post #10 of 11 Old 06-14-2018, 10:23 PM
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Yes, a grain filler is a synthetic material but you apply it to the wood and rub off the excess with a coarse cloth such as burlap. When it dries there is a light haze of the grain filler on the surface you do a little fine sanding to remove. Once you get to that point everything synthetic is in the grain pores. You don't see it in the finish at all.

Working shellac with a sprayer is very similar to working with lacquer. Lacquer just dries a little bit quicker and you don't start with a sanding sealer.
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post #11 of 11 Old 06-15-2018, 08:17 PM
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Eh, for my money a well done french polish looks better than a sprayed on finish, same with the old-fashioned way of filling the grain. Just because something is more modern or faster doesnt make it any better than the old methods. I love spraying shellac, but if i were making an heirloom jewelry box (or god forbid a guitar), id break out the pads and pumice and go at it with some elbow grease. More than one way to skin a cat Steve, you might like your way but that doesnt make anybody elses wrong

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