Spray help

[CEPenworks]

I have been spraying for several years now but have never been satisfied of the results. Here are a couple pictures of my latest attempt. I am using an LVLP Qualspray QS-600 gun. This is a gravity feed. In these pics I was spraying GF's exterior 450. It has a viscosity of 82sec in #4 ford cup. I was using a 2.5mm needle, had the air at 2 turns and the media at 3 turns. The pressure at the gun without the trigger pulled is 20psi. With the trigger pulled it drops to about 0psi. I also have a problem with the air cap getting coated with material while spraying. I try to regularly wipe off the air cap while spraying but stuff still builds up and I have to use my fingernail to remove dried material to keep the air holes on the horns from clogging. Any tips to getting this to lay our better will be appreciated. Years ago when I started spraying I got a mil gauge to test my film thickness. If I sprayed it as heavy as the manufacturer suggests it runs on vertical surfaces. One other thing I had read was you should open up the material screw so that the material flows with a stream away from the air cap not running down the front. I can do that with something like shellac but with any clear that I have tried to spray it always flows down the air cap.

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[jteneyck]

I have been spraying for several years now but have never been satisfied of the results. Here are a couple pictures of my latest attempt. I am using an LVLP Qualspray QS-600 gun. This is a gravity feed. In these pics I was spraying GF's exterior 450. It has a viscosity of 82sec in #4 ford cup. I was using a 2.5mm needle, had the air at 2 turns and the media at 3 turns. The pressure at the gun without the trigger pulled is 20psi. With the trigger pulled it drops to about 0psi. I also have a problem with the air cap getting coated with material while spraying. I try to regularly wipe off the air cap while spraying but stuff still builds up and I have to use my fingernail to remove dried material to keep the air holes on the horns from clogging. Any tips to getting this to lay our better will be appreciated. Years ago when I started spraying I got a mil gauge to test my film thickness. If I sprayed it as heavy as the manufacturer suggests it runs on vertical surfaces. One other thing I had read was you should open up the material screw so that the material flows with a stream away from the air cap not running down the front. I can do that with something like shellac but with any clear that I have tried to spray it always flows down the air cap.

If there is finish filter inside the gun pull it out and throw it away  Filter the finish when you add it to the cup and then don't worry about it.  3 turns on the fluid screw sounds like way too much for a 2.5 mm needle.  I recommend you turn the air screw wide open.  It's a useless feature so I bypass it by setting it wide open.  Something is amiss if the pressure drops to 0 when you pull the trigger.  The air screw may be the culprit, or maybe the fittings or air line coming to the gun are too small, or maybe the pressure regulator is bad or too small.  I typically set my Qualspray gun at 29 psi with the trigger pulled.  It only drops a few psi between trigger off to trigger pulled.   

You need two regulators, one at the compressor set at 90 psi and another within 20 feet or so of your gun to regulate the final pressure.  You need at least a 3/8" hose in the system.  1/4" fittings are OK at the gun, but 3/8" is much better upstream.  This is especially important if you are using a small compressor which I suspect might be the case if you have a LVLP gun.  

John

[CEPenworks]

John,
Thanks for the response. Removing the filter in the gun was one of the first things I learned so I have never used it. I will check my pressures again. I do have a regulator on the gun. When I talk about the air screw I am talking about the fan control not the air volume screw. Do you usually run the fan control wide open?

[jteneyck]

John,
Thanks for the response. Removing the filter in the gun was one of the first things I learned so I have never used it. I will check my pressures again. I do have a regulator on the gun. When I talk about the air screw I am talking about the fan control not the air volume screw. Do you usually run the fan control wide open?

I later wondered if you really meant the fan control.  With my Qualspray gun I set the fan knob at 1 turn most of the time as Jeff recommends in the user's manual for the gun.  That normally gives a wide fan on all but the highest viscosity finish. I almost never change the fan width after I get a good pattern.  So how do I get a good pattern.  I set the fan at 1 turn, set the fluid knob at 1 turn also, then shoot a very short burst on a sheet of Kraft paper or cardboard from 10".  I open/close the fluid knob until I get the most uniform pattern I can.  I normally set the inlet air pressure at 29 psi with the trigger pulled, so that's not a normal adjust for me, and I only change it if I can't get a uniform pattern by adjusting the fluid knob.  I've found that for low viscosity products like shellac and dyes that 20 - 25 inlet pressure works better, so that's where I start now when spraying those products.  

I'll go back to your pressure regulator.  If it's dropping off more than 3 - 4 psi when you pull the trigger something is wrong.  If it's dropping to essentially zero, something is really wrong.  

John