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flow coat for nitro
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=13809		 Page 1 of 1
Author:  BTucker [ Fri Sep 28, 2007 4:05 am ]
Post subject: 

Ok, my first question!


For any of you guys using McFadden's or similar nitro...after much trial and error, I have started thinning my nitro in order to get less orange peel.  My last guitar was sprayed with a mix of approximately 2/3 nitro to 1/3 thinner and reducer.  I understand that you can use a flow coat to get the sanding scratches to melt in, but have yet to use one.  If any of you guys use a flow coat, what ratios of thinner/nitro/retarder (if any)/ are you using?  I know you have to be very careful to avoid sags or runs doing this, but I am thinking of trying it in order to lessen the drudgery of wet-sanding before going to the buffer.
Author:  Brad Goodman [ Fri Sep 28, 2007 4:13 am ]
Post subject: 
Hi Brad,
I use about 10% lacquer thinner and I don't get any (significant) orange peel-so I would start looking at other reasons for this.
Some factors are:
the gun
the air/material ratio
the air pressure
the distance of the gun away from the guitar
etc.
I used to thin that much,but found I got finishes done faster and better with the thicker lacquer.
Good luck,
Brad
Author:  Barry Daniels [ Fri Sep 28, 2007 4:52 am ]
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One way to minimize sanding scratches is to spray a couple of thinned coats after the final level sanding. After letting this cure, start sanding with only fine papers so there are no deep scratches. I usually start this sanding with 1000 grit or so.
Author:  Bruce Dickey [ Fri Sep 28, 2007 5:10 am ]
Post subject: 
Brad G.,

What size tip you using? I like what you are saying here.

Brad T.,

No, I haven't tried a flowcoat per se, but I must be close to it, because I have gotten runs and sags. I just don't have much in the way of sanding scratches wetsanding with 600, 1000, and 1200 before buffing. They just kind of go away. What's your top grit?
Author:  BTucker [ Fri Sep 28, 2007 6:03 am ]
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I had been spraying all my coats (6) uncut, letting cure for a couple of weeks, then wet sanding beginning with 600, 1000 and 1200, then buffing on the wheel  After doing this a few times, and making adjustments in technique, gun settings, experience, I managed to get rid of a lot of orangepeel.  This mahogany one I am doing by spraying 6 coats which are cut in with 1/3 thinner, and I immediately noticed a reduction in orangepeel.  I knocked it down level with 320 dry, then shot 3 more coats cut as above.  Of course, the scratches dissappeard until the thinner flashed off, but I am pretty sure it will level without going through. Prolly shoulda used 600. I did buff one on my handydandy Stewmac buffer one time with coarse and fine compounds after only wet sanding with 600 and the scratches came out, but it was a lot of work, and increased the chances of burning through around the edges.  The gun I am using is an older Sharpe hvlp (the kind with the pressure fed cup). 


I am sure most of my issues are because of me and not the gun.  I was just thinking that carefully shooting a flow coat would help get the finish closer to level than I have achieved so far and reduce the wet sanding process.
Author:  Barry Daniels [ Fri Sep 28, 2007 6:57 am ]
Post subject: 
You should strive for no orange peel when spraying. Usually, cutting back on air pressure will help.
Author:  Brad Goodman [ Fri Sep 28, 2007 7:32 am ]
Post subject: 
Bruce,
I don't know the size of the tip on my gun-it's not an expensive gun.
Over the years I have gravitated towards larger guns with a wide fan.
Author:  Bill Greene [ Fri Sep 28, 2007 12:49 pm ]
Post subject: 
[QUOTE=BarryDaniels] One way to minimize sanding scratches is to spray a couple of thinned coats after the final level sanding. After letting this cure, start sanding with only fine papers so there are no deep scratches. I usually start this sanding with 1000 grit or so.[/QUOTE]

Ditto. This jives with what my guitar teacher does. Usually 3 very thinned coats after the final level sand, and at that point he can start the wet sanding with either 1500, or 2000...OR, go straight to the buffer with medium, then fine. But those last 2-3 coats are thinned solely with acetone to it flashes off very quickly. Worked really well on the one I'm finishing up now.

Bill
Author:  BTucker [ Fri Sep 28, 2007 1:39 pm ]
Post subject: 

[QUOTE=Bill Greene] [QUOTE=BarryDaniels] One way to minimize sanding scratches is to spray a couple of thinned coats after the final level sanding. After letting this cure, start sanding with only fine papers so there are no deep scratches. I usually start this sanding with 1000 grit or so.[/QUOTE]

Ditto. This jives with what my guitar teacher does. Usually 3 very thinned coats after the final level sand, and at that point he can start the wet sanding with either 1500, or 2000...OR, go straight to the buffer with medium, then fine. But those last 2-3 coats are thinned solely with acetone to it flashes off very quickly. Worked really well on the one I'm finishing up now.


Bill, how much acetone are you mixing with the lacquer?  That's my goal...to eventually be able to pretty much go straight to the buffer.

Bill
[/QUOTE]

Author:  Bill Greene [ Sat Sep 29, 2007 1:25 am ]
Post subject: 
Brad:

It's a lot. Probably 40% acetone, at least. It runs quickly off the stick, and it flashes so fast that it's dry to the touch in a minute. But I do need to add this: he's very, very, almost insanely picky about the pore fill, which makes the first two level coats (which are spray, dropfill if needed, level with 320, respray, level with 600) much easier, as it eliminates any sagging, and minimizes the need to drop fill. So by the time you get to the flow coats, you're just down to the pretty stuff...the hard work is done.

On my recent guitar, although I "started" wet sanding with 1500, I could have started with 2000 and it would have worked fine...just used up a bit more sandpaper and elbow grease. And a buddy swears he can start there with the buffer and a medium compound, and move straight to a fine compound, and then do minimal touch up with polish...but I haven't seen it yet. I'm only on my second build.

If you'd like, next time I talk to him I'll get the "exact" ratio. Not a problem.
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