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Yankulele
05-17-2016, 04:02 AM
I wonder if builders would be willing to share their technique for finishing out nitro. I have my first two ukes to be finished in nitro hardening up now. I sprayed three coats over pore fill of CA in one (walnut) and shellac in the other (cherry), sanded with 400, then sprayed three more coats.

After 10-14 days, I plan to finish sand and rub out. I have the Micromesh papers in both the squares and the discs for the ro sander. I'm a little too scared to use the RO, because I'm afraid I'll cut through on the edges.

Would working up from the 2400 through the 12,000 and buffing with Meguiar's fine cut cleaner seem about right? The micro mesh works wet and dry. Any reason not to use it dry?

Thanks,

Nelson

mzuch
05-17-2016, 06:34 AM
I always wet sand on nitro, never dry. And I've never used a RO sander, which I fear would be too aggressive. I level sand (by hand) with P360 between build coats. When the final coats are on and cured, I use P1000, then P2000. I then buff with the fine Maguires polish and again with Maguires swirl remover. (I don't use micromesh so I don't know what the equivalent grits are.)

Moore Bettah Ukuleles
05-17-2016, 07:51 AM
You're on the right track Nelson, especially if you're building single ukuleles. I find using the RO sander to be about 4X faster than doing it by hand and the finish looks better as well. The problem with hand sanding is picking up stray pieces of larger grit or other contamination, producing long, deep scratches that won't show unit you progress to the higher grits. With a ROS the scratches made by sanding are tiny little circles, easier to buff out. An ROS is faster but that also makes it more dangerous. In either case it's important to keep your environment as clean as possible when sanding and buffing finishes. I have dedicated sanders that never see wood, only lacquer, and are sealed in plastic bags when not being used.

BTW, I believe that 2400 micro mesh is equivalent to about P800. NEVER sand any finsh dry. To flatten, I'd rather start with something finer, say P1000 or even P1500 (Micro Mesh= 3200). I don't care for the cushioned (cloth) backing of MM for flattening, preferring a more rigid paper like Mirka. Mirka papers are excellent, very consistent, long lasting and will not pill if you add a few drops of Dawn detergent to your water.

You talk about six coats of lacquer total but that really tells us nothing about the thickness. That will vary depending upon the brand of lacquer, the ratio of reduction, and your technique in spraying. If you've got orange peel you'll be sanding more of your finish. I like my final coats to build up to about .006" which will sand down to about .004" when I'm finished. Many sand-throughs can be eliminated by spraying your corners first, then spraying the overall instrument. Sharp edges do not like to hold lacquer and this method makes sure you'll have adequate coverage on those critical parts. Also, never sand your edges, they'll take care of themselves. I power sand all my finishes using either Abralon or Trizact (after first hard blocking with 1000) up to P5000 before buffing (two compounds) and rarely have a problem with sanding through. They say that is your butt isn't clenched all during the final sanding process, your finishes are probably too thick. :) You're working right on the edge all the time.

Power sanding lacquer is wonderful in a production environment and I wouldn't do it any other way. If you are building the occasional instrument and have more time than experience you might be better off doing it by hand. Good finishes are an art that is only learned through lots of practice. It's by far the hardest thing I do. Good luck.

Beau Hannam Ukuleles
05-18-2016, 06:05 AM
Chuck,

Which RO wet sanding hook n hoop papers are you using??- i cant seem to find any Mirka ones that aren't foam backed.

Perhaps Abranet HD??
http://www.mirka.com/en-US/us/abrasives/abrasives_by_substrate/#/Lacquers

Yankulele
05-18-2016, 11:19 AM
Thanks Mzuch and Chuck.

I will do the first one by hand, and then see how brave I feel for the next one. I do have a lot more time than experience, so I guess I will continue to trade the one for the other.

As far as my lacquer build, I don't know actual thickness. I am using Cardinal gloss, diluted in a 2:1 ratio (lacquer:thinner) using the Cardinal lacquer thinner. My last couple of coats went on wetter than the first, and flowed out nicely with little orange peel and no runs.

Do you mic your top before and after spraying to gauge how thick your finish is?

I think I will start with 2000 wet/dry on a cork block with soapy water (is Palmolive ok?) and see if it is aggressive enough, and then work up.

Thanks again,

Nelson

Beau Hannam Ukuleles
05-18-2016, 11:33 AM
To cut back the first coats, and knock the top off the other coats use something like 320, 400, 600.

2000 grit is for the final cutback just before buffing.

Yankulele
05-18-2016, 12:39 PM
Thanks Beau. I used 400 between the first three coats and the next three coats. It's pretty smooth now, after the last three (six total), and my thought was to cut back with the 2000 and then buff. Although, I do have some 3000 I could use after the 2000 and before buffing. Not sure if that is an extra, unnecessary step risking burn through.

Nelson