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While leveling nitro (not pure, has some alkyd and acrylic resins too) I have absolutely zero luck using faster grits (P 800 or 1000 of several brands, micro mesh 1500 to 2200) without scratches. I've been very careful to constantly have plenty of soapy water on the surface, that the pressure is very low and that the abrasive does not clog (very often rinsed and checked). Lacquer seems cured enough (waited 2 weeks or even 7 same result) and i can't scratch it with the nails.
Papers are soaked in advance and i tried several types of pads or just fingers.
I then continue with p 1500, 2000/2500 or mm 3200 and then it machine buffs beatifully (medium fine extrafine colortone compounds then swirl remover by hand) but under close inspection there are hundreds of leftover​ scratches.
They are deep enough to require very lengthly sanding with p 1500. The medium compound has no effect even when leaning hard on it for minutes.


What i finally managed to do without scratches is to simply start from 1500 (sunken pores) or even 2000 (nice areas). It requires a fair amount of elbow grease but especially with 2000 it seems 100% safe and in the end faster than going back to fix scratches and rebuff.

Perhaps i should try a coarser compound than the colortone medium. Menzerna medium?

Thanks for any suggestion!

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Before anyone suspects I have two left hands, this is the reflection I am getting, flat as a mirror. But at low angle viewing the scratches are obvious.

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And another problem I have is that the fine compound very easily piles up on the lacquer. Then I need to do some elaborate scrubbing with a cloth to get rid of it. Extra fine seems OK but I rub it very gently. Do I have too much fine compound on the wheel? Too much pressure? The medium doesn't pile at all even if i rub very hard or overload the wheel.

Thanks!

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I'm sorry I cannot help you because that would be perfectly acceptable to me, in fact I'd be thrilled

I feel your woes, I hater finishing the finish

I can't help you at all. I've been finishing guitars for over 50 years with nitro and lately I get the same results you do. I think it has something to do with the modern finishes (additives) proscribed by the greenies and epa. Your finish looks good and I suspect your customers will be happy with it.

I'm with JF; I would love to have a finish like that. I do admire your pursuit of perfection Alexandru - I'm sure that explains the beautiful results you are getting,

I keep working on my finishes (french polish) until I find myself going in circles and not improving the product, but each guitar moves that point forward a bit
Mike

Not sure of your complete process --- but I was getting those pesky defects until I started leveling with nothing more course than 600 grit --- I am talking about between coats leveling not final polishing. In others words when I used a grit progression I was getting those mystery defects I assume because I missed some scratches by moving to the next grit too soon.

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Ken Cierp

http://www.kennethmichaelguitars.com/

I have also gone to using nothing finer than 600 grit for leveling early coats and am trying to level my final coats with 1000 or finer. Of course then I get impatient and end up with the tiny scratches. If I can get by with only 1000 or above after the final coats it does seem to come out better, but then the better it looks the more he little flaws stand out. I'm beginning to think I must come to the point of an acceptable finish rather than the best finish I can possibly get.

Kent

I dont wet sand nitro anymore since i started using Super Assllex. I just start with there 600 grit stuff and go up to their highest, about 1600 i think. It cuts quickly and leaves shallow scratches.

But i suspect my eye is not near as keen as yours

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Joe Beaver
Maker of Sawdust

You could try wet sanding with the 3M trizact sanding discs. They are generally used by auto finishers, but I have used them on solid surface materials and lacquer finishes. Some people use them for polishing plastic headlight covers.

I think you're just expecting too much. Hardly a git I finish doesn't have some minor, minor "scratches" when looked at at an angle. When I get reflection like you have in the pics I consider it done. And done well. And I should add that I used to be bothered by them but I don't anymore.
Finally- good job!

Thank you! I am excited about the gloss, just that seeing scratches is equally letting me down I managed to get to terms with the imperfection I had on french polish, but nitro is new to me. Sprayed 4 guitars, finished two by hand and the buffer came a couple days ago.

In between coats I sanded every 2 coats, dry with Abranet 240 after the first few and then 400 before the final 2 coats. I might very well have grit or dust embedded in the lacquer. Evil grit scratching seems especially noticeable with micromesh. I start with 1500 (which is in between P600 and 800) it goes well then I can distinctly hear haaarsch haaarsch. Before posting I was suspecting that these coarse abrasives simply have the occasional bad grit on then. I can accept that on a cheaper wetdry paper but on micromesh? So again, what if it is gunk that deposits when spraying. My spray room is dirty and dusty (I have the drum sander there and so on). However, why it does not happen if I start with 1500 or 2000? They should eventually free up whatever is bad within the lacquer too.

I could do the pre-final level with finer (Abranet 600, or even 1000 paper) but these clog too easily. I was afraid to use soapy water - can the soap residue ruin adhesion? Perhaps best is not to level in between at all. I spray thin and wet, shouldn't have any adhesion problems even if it dries overnight in between coats.

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Some progress i think. This morning I started again with rough MM 1500, but rather than going back and forth (or God forbid in circles) I sanded only in one direction. Drag, lift, reposition, drag etc. I think this way whatever scratcher is there tends to stay towards the outside of the sanded area instead of being constantly agitated in the middle. Perhaps it is wetsanding 101 but I don't think i saw this stressed out in tutorials.

Then I followed with MM 1800, 2400, 3200, 6000 (pretty fast, a couple mins each). Less than 1 min on the wheels and it is glistening and free of problems.

This was just a smaller area on the sides, the real test will be on the back, fingers crossed.

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, fingers crossed.
Best tip I had (from Mario Proulx) was sanding at 45 degrees, then at a right angle to that (45 other way), with the last grit along the grain.
This lets you see when you have sanded out all the scratches from the previous grit at each stage.
But I suppose everyone finds their own way.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Yes changing direction with the next grit is great for revelatory purposes. In college, when preparing metal samples for microscope analysis we were thought to go through every grit and cross the previous untill all marks were gone.

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Try starting with a finer grit. I start with 3200 mm to get it close to level with a few shiny spots left and then move to 3600 and work all the way up to 12000. I don't use a powered buffer. It is a lot of work, but I like the final result.

I think Ken is right. Sanding to a uniform 1000 grit from 600 is something that will mostly show when you go to 1500. I used to double sand after about 2000 grit when the shine starts and just like that, the scratches start to appear. That is when you realize that you have not fully sanded at 1000 grit. It's just a matter of going back and sanding the scratches out. Sanding and buffing is not a straight thru shot.
As far as when to quit sanding, yes, some like to stop at 600 and buff, but I did it to 4000 grit and buffed. Less dust when wet sanding and less buffing dust.
Something else to consider...you will never achieve a "perfect" finish.

Alexandru,
Just noticed the bottle of 96 proof. Are you using that for the wet sand?

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Joe Beaver
Maker of Sawdust

Is this for a customer or for yourself? If for yourself are you going to ever play it or put it in a glass case and display it. Because five minutes after you are finished getting a finish even God would be envious of it will get a scratch and you will have put too much time into perfection that will not last.

Just my two cents worth.