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High gloss sanding tip

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Forum topic by difalkner posted 06-13-2018 08:18 PM 336 views 0 times favorited 6 replies Add to Favorites Watch
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difalkner

121 posts in 1929 days


06-13-2018 08:18 PM

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

-- Nothing to do with woodworking at all, just our music at church (I'm the guy with the Koa Takamine) - https://www.youtube.com/channel/UCSpLecPAn4AJEp6qHC7C44A


6 replies so far

View lew's profile

lew

12102 posts in 3782 days


#1 posted 06-13-2018 09:34 PM

Thanks for the tip!

That’s going to be a beautiful guitar when it’s finished!

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View difalkner's profile

difalkner

121 posts in 1929 days


#2 posted 06-14-2018 03:24 AM

Thanks, Lew! It’s been a fun project that I want to repeat another 15-20 times, sans mistakes, of course.

David

-- Nothing to do with woodworking at all, just our music at church (I'm the guy with the Koa Takamine) - https://www.youtube.com/channel/UCSpLecPAn4AJEp6qHC7C44A

View johnstoneb's profile

johnstoneb

2942 posts in 2199 days


#3 posted 06-14-2018 05:52 PM

True French polish does not require sanding.

-- Bruce, Boise, ID

View difalkner's profile

difalkner

121 posts in 1929 days


#4 posted 06-14-2018 06:53 PM

I’m sorry, Bruce. I’ll throw it away…

LOL! Learning, simply learning, and I’m not French so it’s gonna take a while.

David

-- Nothing to do with woodworking at all, just our music at church (I'm the guy with the Koa Takamine) - https://www.youtube.com/channel/UCSpLecPAn4AJEp6qHC7C44A

View Rich's profile

Rich

2998 posts in 616 days


#5 posted 06-14-2018 07:13 PM

What a beautiful guitar. That’s a good example of using sapwood for a dramatic effect. I really like it.

However, I do have to take issue with the premise of the thread. I haven’t found that sanding twice as long is required going from grit to grit. Perhaps if you went straight from 80 to 600, you’d be at it a long time, but if you don’t skip grits, you are removing finer and finer scratches with finer and finer paper. That sounds pretty linear to me. Besides, once you get into the finer grits, I think it’s time to switch to hand sanding with the grain where scratches aren’t much of an issue.

Here’s a quote from Tim Inman’s book The Art of Classical Furniture Finishing that’s similar to what you’re saying though, so there is something to it:

“My Dad and my Grand Dad both told me that if I went across
the grain one time, then it took 20 times with the grain
direction to fix it.”

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View difalkner's profile

difalkner

121 posts in 1929 days


#6 posted 06-14-2018 08:52 PM

Thanks, Rich! When I cut the pieces off the slab of Mahogany I couldn’t wait to bookmatch them because of the sapwood. A friend, who didn’t know any better, asked if I planned to stain that and see if it would blend in to match the rest of the guitar. I explained that look is desirable and he was surprised.

I like your quote. Obviously my tip isn’t a hard and fast rule but more a thought to keep in mind so we (I) don’t just give the finer grits a light whisk and call it good. Let them do what they are designed for and get a better look with any finish you use.

David

-- Nothing to do with woodworking at all, just our music at church (I'm the guy with the Koa Takamine) - https://www.youtube.com/channel/UCSpLecPAn4AJEp6qHC7C44A

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