Official Luthiers Forum!

Greetings! I am having a wee bit of trouble spraying. I am having a hard time getting a perfectly smooth coat. I am getting what I've heard referred to as a 'pebbly' texture. I've monkeyed with the air pressure/amount of liquid etc but am not having much luck. I am spraying KTM-SV. My gun has a 1.5 mm nozzle, if that's relevant. Any tips would be greatly appreciated.
Thanks

Check out Pheonix Mandolins. Rolfe uses KTM-SV & has a lot of info on his site. (He may also offer tips if you e-mail him).

_________________
Dave
Milton, ON

Disclaimer: I haven't sprayed any KTM-SV, and I've only sprayed waterbornes a couple times.


(Most) Waterbornes dry really fast. It will actually start drying in the air if the gun is too far away from the piece you're spraying. Spraying (anything) too thick can cause a pebbly texture. You may try thinning it a little (with water???) Too much or too little air pressure can also cause problems. The finish needs to be atomized instead of being in big drops. Too much air pressure can cause it to actually bounce off the surface, and cause texture. Too little air is what causes the big droplets instead of being finely atomized. Yoy kinda want a fog coming out of the gun. I would guess that a 1.5 tip is plenty big enough for KTM-SV. If a tip is too big you can usually compensate by either adjusting the fluid control, or not pulling the trigger all the way.
Try this, set the air pressure a little under the max recommend for the gun. On a piece of scrap (or a wall that doesn't matter) barely pull the trigger, just enough for air. Slowly pull the trigger more, and keep pulling more and more as you spray across the scrap. Is there a point where it's.....right? If there is that's where you want your fluid control. If it's bad all the way increase the air pressure, and try the same thing again. Keep messing with the pressure to see if you can find a "happy" place. I've got guns that like a pretty good bit above their recommend PSI with certain materials. If you can't find a "good" place try thinning the finish some, and try again.

_________________
I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

HVLP? Sounds like an air pressure / fluid flow issue. Check the recommended pressure for your gun. Hopefully you have a gauge at the gun. Set the pressure at the compressor reading the pressure at the gun with the trigger pulled (don't set the pressure using a regulator at the gun). Start with the pressure close to the max of what your gun manufacturer recommends then make adjustments with the fluid control until you get what you are looking for.

Ken

_________________
http://www.casperguitar.com

Thanks everyone. I think it probably is just a matter if fiddling with all the dials. I increased the air pressure quite a bit and that seems to have helped. I guess I just need more practice getting the right balance between too little paint (pebbly) and too much paint (runs)...

http://www.newenglandluthiers.org/conte ... inish.html

This is a link that will answer your question. It is by Phoenix mandolins. He says this is an issue with spraying too dry, or too light a coat. It is a tough thing to get the feel for. Poor flow is either too thin of a coat or too thick of material. Make sure that the finish itself is warm, no leaving it in the cold garage or anything, that will mess it up. I find that a hand held shop light is really helpful to see the thickness and flow of the finish, it takes just the right angle of view and light to really see it do its thing when it flows from a million microdots into a smooth pool. I have the light in one hand and the gun in the other so I can quickly add a bit to a light spot.

If your fog gets too light, it does have that drying in the air thing happen. I do spray water base lacquer hvlp. My setup and method to adjust is to leave the compressor high, then with a gauge on the gun I turn it down pretty low, maybe 10-15lbs. With the needle all the way in, or closed, I start to back out the needle, I go a little past where it starts to spray and begins to get a bit splotchy, then I bring the air on the handle up till I get the fog I want. I spray with a 1.0 needle on a Binks gun. I think the 1.5 may be a bit big, so this method may help. I do find that I do not get a good spray if the needle is too closed. I prefer a slightly heavier spray with a faster hand motion to be helpful in getting flow without drips.
Rob

_________________
http://shastaguitar.com/
http://www.kalimbakit.com/
http://www.youtube.com/user/comfyfootgr ... ature=mhee
http://www.facebook.com/robert.renick.7

also, spray so the surface looks "wet".
This with a little methanol, say 2-3%I spray out my gun with methaol then add the waster base finish and go to it

_________________
Greg
http://garibaldiinstruments.com/