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  #166  
Old 01-08-2019, 06:32 PM
ruby50 ruby50 is offline
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Ouch

thanks Tim

Ed
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  #167  
Old 01-08-2019, 07:33 PM
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Tim,
I have always wondered about the grit of sandpaper being used on tonewood. To my way of thinking,320 grit paper is extremely rough and would leave deep scratches, which would then require finer grits to sand out the scratches.

My reference points come from my career in the automotive industry. Various components that have been heat treated for example must be hardness tested to ensure they meet the required specifications. Now, I have considerable experience in polishing small test parts that will be placed under a Microvickers machine for the purposes of determining this surface hardness. These surfaces must be polished to a mirror finish and completely scratch free. I usually start with a 320 grit paper but work my way up to 1200 grit paper and finally a buffing pad to achieve the needed results.

In working with tonewoods, why are you not striving for a completely smooth surface finish before applying the lacquer? Or is 320 grit smooth enough because the wood surface will eventually be covered up? Or maybe it’s because you aren’t polishing the wood surface, but rather leveling it in preparation for lacquer? Sorry for so many questions, but I’ve wondered about this for some time.

Love your threads BTW, especially the engineering that goes into what you do. We’re I ever able to have a guitar built, I can’t imagine having anyone but you build it.



Hi Ron,

Finish “systems” are quite complex and each type requires one to follow the manufacturers directions to achieve the best results.

Bare wood must have a certain amount of roughness or surface texture for the finish to adhere to. Some finishes are more critical than others. Shellac will adhere very well to a very smooth surface, even glass, while lacquer, urethane and poly-urethane will easily delaminate or peel off. The latter three require an abraded surface texture for the finish to grip to.

Polyester will not cure over bare wood and it requires an “isolante” sealer, usually a catalyzed urethane based sealer where the sealer mechanically binds to the wood and the Polyester binds chemically to the sealer. Different finishes types require different sealers or base coats.

Nitro cellulose lacquers can be applied over shellac or a catalyzed vinyl sealer. Lacquer likes an abraded surface for the first coat to bond to and then successive coats of lacquer burns in or melts into the previous coat.

Shellac works similar to lacquer in that successive coats melt into the previous coat. Both of these finishes cure by solvent evaporation.

Varnish is usually applied over a shellac sealer but successive layers will not adhere to the previous layer unless you abrade or sand the prior coat.

Urethane and polyurethane is similar to varnish in that you must sand between coats so the new coat has a toothed surface to mechanically bite into. These two finishes cure by solvent evaporation.

Musical instruments typically use finishes that sit proud of or on top of the wood itself. Penetrating oil type finishes are not usually used on musical instruments because they (can) dampen the wood where as a (thin) finish that is applied to the surface of the wood has less affect on the vibration properties of the wood.

I’m currently using a catalyzed urethane / lacquer top coat which requires a catalyst for it to chemically cure. It requires a sealer or barrier coat between the bare wood , or pore filler, and top coats. The sealer sticks to the wood or pore filler and then the cat/urethane lacquer mechanically bonds to the cured and abraded sealer. You usually apply 3-4 finish coats, wet on wet, in one day so that it burns into the previous coat within a limited time frame. Each coat will burn into the previous coat (IF) it’s applied within the pot life of the catalyzed finish, which is usually 4-8 hours. If you don’t apply the coats within the required time frame then you must sand the previously cured coat.

I sand the bare wood, filler, sealer and finish with a random orbital sander which leaves a very consistent surface finish. If I am staining bare wood then I must sand it to 320 or the stain will reveal the sanding scratches of any coarser grits. If I am not staining the wood, I usually sand to 220 to provide more tooth or surface roughness for my finish system. 220 Random orbital scratches don’t show through the finish product that I currently use. I typically use 320 grit to sand finish between sessions. I could use 220 but it removes more finish and I’m not trying to remove finish but rather trying to build it so 320 provides enough tooth between sessions without removing too much finish.

Sorry for the long reply but each finish system has its own set of peculiararities and may use a different sanding schedule unique to that finish type or system.
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  #168  
Old 01-08-2019, 07:44 PM
FLRon FLRon is offline
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Thanks Tim. Suddenly it all makes sense!
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  #169  
Old 01-08-2019, 07:57 PM
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Originally Posted by FLRon View Post
Thanks! That does help to clear things up. So sanding the wood too fine increases the chance that scratches and swirls wil show through the finish.

Thanks for the link ruby50!
Just the ooposite IME. Coarse sanding scratches will show through the finish more easily. You can get by with coarser grits hand sanding with the grain but random orbital sands in small circular motions so it requires finer sanding grits, depending on the finish system and if you are staining the wood or using colored pore filler.
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  #170  
Old 01-08-2019, 09:51 PM
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So sanding the wood too fine increases the chance that scratches and swirls wil show through the finish.
No, that's incorrect. Just the opposite is true. And with a guitar, I would never consider final sanding to be done by a random orbital; I think most builders will agree it's best to scrape or hand sand with the grain.
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  #171  
Old 01-09-2019, 06:53 AM
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Originally Posted by runamuck View Post
I would never consider final sanding to be done by a random orbital; I think most builders will agree it's best to scrape or hand sand with the grain.
Well to each their own. I feel I have as much or more control sanding with a RO sander than I do hand sanding. Heck, I've burned up 4 or 5 RO sanders in the last 25+ years. I still do a fair amount of hand sanding but that is generally limited to edge and outside corner radii and some inside corner radii on the neck. I use a RO sander on all flat surfaces, top, back and sides.
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  #172  
Old 01-09-2019, 07:31 AM
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Originally Posted by FLRon View Post
Tim,
My reference points come from my career in the automotive industry. These surfaces must be polished to a mirror finish and completely scratch free. I usually start with a 320 grit paper but work my way up to 1200 grit paper and finally a buffing pad to achieve the needed results.

Love your threads BTW, especially the engineering that goes into what you do. We’re I ever able to have a guitar built, I can’t imagine having anyone but you build it.


Hi FLRon,

Thanks for following along with us on this thread. Sorry but I overlooked addressing one of your questions. Finishing wood and finishing metal are two different animals but share some similarities. When you polish metal surfaces you are progressing through sanding grits to remove scratches from the previous grit and as I am sure you know, you just can't take short cuts and skip grits or you'll be unable to remove deep scratches with too fine of grit sandpaper. In simplest of terms, you are systematically removing material from the base metal surface to achieve your final polished finish.

When working with wood we are relying on the top coat finish product to give us the final mirror gloss instead of the wood itself. Yes, the wood must be sanded to a certain smoothness before the finish is applied but its not the wood itself that shines but instead its the finish on top of that wood that gives us the gloss.

BTW, all finishes have a specific gloss rating measured on a scale of 1-100 with the higher number having the highest gloss. Just because a finish might have a flat, satin, semi-gloss or gloss "generic" rating, the OEM has also assigned each finish a corresponding gloss measurement number and you can find that number if you dig into the fine print or make a few phone calls or emails. The catalyzed urethane lacquer product we currently use has a 98 gloss rating which is one of the highest in the industry. I've never seen a 99 or 100 rating on any other products but they may exist? Many finishes are in the low 90s and some polyesters are down in the low 80s due to the higher solids content. Satin products have dulling agents added to the product to retard clarity and light refraction.

Just because a product has a 98 rating its not magically a 98 after its sprayed onto the surface of the substrate you applied it to. To achieve the highest gloss rating of any finish product the cured finish must be sanded in a similar manner in which you prepare metal. We typically sand our current finish with 600, 800, 1000, 1500 and 2000 grits before power buffing with four grits, medium, fine, very fine and hi-polish buffing compounds. Its only then that it has a 98 gloss rating.
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  #173  
Old 01-09-2019, 07:55 AM
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Here I am starting the sanding process of the cured finish in preparation for buffing. I am dry sanding with 600 grit sand paper and if you look closely at the glossy edge of the finish, where the sander has turned the finish white, you will see hundreds of little dark spots.

After the liquid finish is sprayed on the guitar's surfaces it dries with a surface texture that is called "orange peel". The dried finish surface looks very similar to the surface texture of an orange. The amount of orange peel can be minimized by the skill of the person spraying the finish, the quality of the spray gun, the amount of air used to atomize the finish, the velocity of the finish application and the viscosity of the liquid finish. There will always be some amount of orange peel, no matter what type of finish is sprayed. Some finishes will have more orange peel, usually because they dry faster and some finishes will have less orange peel because they dry slower and the finish has more time to flow out. Slow drying finishes are more difficult to spray because they have a greater risk of the finish sagging or running on vertical or curved surfaces.

During the first initial sanding, I am cognizant of the orange peel and my goal is to sand the surface level to remove all of the tiny dark spots or orange peel. Then I know the surface is completely flat.

All subsequent sanding courses are done to remove the previous sanding scratches. For example, after the first sanding session it leaves 600 grit sanding scratches so the second sanding course I would use 800 grit sand paper to remove the 600 grit sanding scratches. The next course is sanded with 1000 grit to remove the 800 grit scratches and so on until I finish sanding at 2000 grit.











Grits 1000, 1500 and 2000 are done by "wet sanding". The sanding grit are so fine on these papers that the sand paper easily loads or clogs up with finish particles and then the sandpaper becomes ineffective. By sanding with a mixture of water and soap, it lubricates the sandpaper and keeps the finish from clogging up the sand paper.
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  #174  
Old 01-09-2019, 10:47 AM
Halcyon/Tinker Halcyon/Tinker is offline
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What brand paper is on your ROS?
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  #175  
Old 01-09-2019, 11:39 AM
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What brand paper is on your ROS?
Hi Ed,
I’m currently trying Klingspor for wood and finish. However, I’ve found that Grizzly gold works better on raw wood and Mirka Gold is better for wet sanding. I also use Abralon 2000 as my last wet sanding course before buffing. I’ve wantd to try 3M plastic film discs for finish but have yet to exhaust my supply of other sandpaper brands on hand. BTW All my papers are hook and loop.

What are your preferences in sandpaper’s?
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  #176  
Old 01-10-2019, 12:10 PM
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Making it all nice and shiny:















Peeling the Frisket film from the bridge gluing area:










Frisket film is .001" thick. The caliper reads .0025" minus .001" of the Frisket film, which shows the actual finish on the top is only .0015" thick. For reference, a sheet of computer printer paper is ~.007" thick.
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  #177  
Old 01-10-2019, 12:31 PM
GaultierRedon14 GaultierRedon14 is offline
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Wow, that is impressively thin, Tim! Looking forward to a super thin finish like that on the upcoming build.
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  #178  
Old 01-10-2019, 02:30 PM
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Great info Tim! I haven't had time for quite a while to review your thread, but I took some time today to read some of your educational info regarding finishing and learned quite a bit.

Your work looks awesome. I hope to get the opportunity to play one of your guitars soon!
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  #179  
Old 01-10-2019, 04:42 PM
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Wow, that is impressively thin, Tim! Looking forward to a super thin finish like that on the upcoming build.
Since this one is coming to a close, yours will begin VERY soon
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  #180  
Old 01-10-2019, 04:43 PM
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Originally Posted by invguy921 View Post
Great info Tim! I haven't had time for quite a while to review your thread, but I took some time today to read some of your educational info regarding finishing and learned quite a bit.

Your work looks awesome. I hope to get the opportunity to play one of your guitars soon!
Hi Mike,
Thanks for stopping by to check this thread out. I look forward to meeting you someday as well and putting one of our guitars in your hands.
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