High gloss sanding tip - Router Forums
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post #1 of 34 (permalink) Old 06-13-2018, 04:01 PM Thread Starter
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Default 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

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post #2 of 34 (permalink) Old 06-13-2018, 05:02 PM
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Hmmm...
In effect you're saying that each time you sand you're taking everything down to the level of the bottom of the deepest scratch.
My attitude, reached after learning from drywall finishers, is that you remove the high spots...and that's a bit subjective...then fill in all the low lying landscape with the next coat. All scratches disappear until you start sanding again; this time with a finer grit.
A different approach, with the basic difference being that the depth of finish is building up in thickness, not being reduced to very close to what it was on the previous coat.
I'd love to hear from any of the car restoration guys here; what's your process with multiple lacquer coats?
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post #3 of 34 (permalink) Old 06-13-2018, 05:10 PM
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As a side note, in the Drywallfinishing final practical exam up here, the students aren't allowed to touch the project with sandpaper* until the final coat of mud is dry. ie the approach that I described above. Each successive coat buries the low lying faults.

* not suggesting that's a perfect analogy; just a different perspective.

Last edited by DaninVan; 06-13-2018 at 05:12 PM. Reason: added text
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post #4 of 34 (permalink) Old 06-13-2018, 06:01 PM
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Quote:
Originally Posted by difalkner View Post

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.



David
....and thats the key to success David.... knowing exactly where you are at within the process!!! Messing up at this point can be fixed, but not without alot of work. Pay very close attention to almost every single detail, every scratch, every low spot, every high spot, the edges, the curves, the pressure on the sanding mediums and for me, most importantly every "reflection". In the picture I added, I'd give the job an 8 outta 10. The reflection is the tell of the tape. This particular job was finished off with Minwax rattle can lacquer, a wet sanding schedule very much like what your doing and then I used Griot's Garage car polishes. Prior to using the Griots product, I used McGuiars car polishes.

Beautiful job thus far David....
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post #5 of 34 (permalink) Old 06-13-2018, 06:04 PM Thread Starter
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Kind of the same thing, Dan. I use the 320 to level the surface, even though it is very flat and level now but I make sure there aren't any shiny spots I've missed. The 400 makes the scratches even finer but if you don't do it enough then there are deeper scratches that the 500 or 600 has trouble removing. If you use the next finer grit to remove the 'coarser' grit scratches it just takes longer until they're all gone. In this case with a high gloss sheen the scratches from the 320 would show if I didn't remove them with the 400. The 400 scratches would show if I didn't remove them with the 500, etc.

So what I've found is that it takes roughly twice as long with the next finer paper to remove the scratches from the coarser paper. Whether you're sanding 100 grit on bare wood and going to 120 grit or sanding with 180 and going to 220 and on to 320. People have asked me how long on each grit and the general guideline I've given is what I've stated here - about twice as long on the next grit as you did on the previous grit.

David
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post #6 of 34 (permalink) Old 06-13-2018, 06:09 PM Thread Starter
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Thanks, Bill! And that's a beautiful chess board - wow! I'll be using Meguiars once I finish with the Micromesh papers.

Another good tip on sanding is get the edges right and the middle sort of takes care of itself. All too often the edges are the indicator of a good finish job. It's easy to work on the easy middle part for finer sanding but people are afraid of burning through or rounding edges and a lot of finishing jobs I've seen show that people stayed away from the edges for that reason.

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post #7 of 34 (permalink) Old 06-13-2018, 06:13 PM
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@DaninVan

I'll just give you my own perspective and try to answer your query... You're pretty much spot on with the "scratch" concept. You take out the bigger scratches with smaller scratches. With a mirror finish such as David's, you're taking that scratch pattern down to the point of not being able to notice the scrach's at all. And you keep on going from there. You're not only working the finish, you're also working the wood as well. Not only does the laquer have its high/low spots, but the wood itself has em. Once you get to the point that you are satisfied with the wood you move onto the finish. But even the best prepped pieces of wood will have its own high/low spots when you are attempting to achieve this level of a finish. Now you can either work those first few coats of finsih back down to the high spots in the wood and build up the low spots in the lacquer or avoid going back down to bare wood and just work on building up the low spots in the lacquer. Personally I find larger flat panels MUCH easier to deal with than those such as David is working with here. Curves, bends and bows all add to the difficulty of creating a surface that just flows smoothly and evenly. This is where I've come to rely on the reflection. The crisper and the sharper the reflection the closer you are to where you wanna be. Hope that kinda sorta maybe helped..
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post #8 of 34 (permalink) Old 06-13-2018, 06:15 PM
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David...

DO NOT give the car polish a try until you have tried it and experimented with it. I'm sure I don't have to tell ya how I know this *L*

"..... limited only by imagination"

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post #9 of 34 (permalink) Old 06-13-2018, 06:18 PM
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I've never heard of using such fine grits. I would use a card scraper to get a near perfect, high gloss surface. All that sanding has got to raise the grain, and you're going to lose a LOT of wood in the process. A card scraper requires a bit of practice, but makes a beautiful surface.

The more I do, the less I accomplish.
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post #10 of 34 (permalink) Old 06-13-2018, 07:02 PM
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David... are you block sanding or just using your hands?

"..... limited only by imagination"

"Just smile and wave boys, smile and wave"
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