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Painting with a gravity feed spray gun

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  • Painting with a gravity feed spray gun

    Calling on people experienced with gravity feed guns!

    I gave my compressor a trial run today (side note: must stop jumping every time the motor kicks in!).

    I'm having trouble getting used to the gravity fed paint gun:

    Firstly: I've set the output pressure of my compressor to 43PSI as recommended by the paint gun.

    Just for a test, I used some water based undercoat/primer that I had previously diluted for a dedicated spray paint gun that I doubt has as much pressure as this air compressor, so I think thats my first mistake (too thin).

    With the old 'dedicated paint gun' I was using it had a supplied funnel that you used to measure for the right viscosity of the paint. If it took between 25 & 30 seconds to drain through the funnel, it was right.

    How do I do a similar thing with this new compressor/paint gun I have? Is there a rule of thumb for paint/thinnner mix? Someone here suggested that gravity fed doesn't need thinning at all?

    Basically when I painted I found:
    • The needle adjusting screw did nothing noticable.
    • The 'Pattern' knob turned it from being practically a hose (coming out in a very thin but heavy jet that I had to paint from a meter away) to a more narrow jet of mist. I can't quite tell how to adjust from the circle to the oval arrangements with this knob yet.
    • The 'air adjustment' knob was turned all the way in one direction. As soon as I adjusted it any other way, paint would basically 'spittle' out in little blobs that would go about 20cm and then drop on the floor (ie had no force, as if it wasn't being blown).

    With best configuration I was getting too much coverage (runs) and it was going on 'blotchy' like little (overly large) blobs of paint which would run together. Again I suspect the paint was too thin. Here's a photo, but keep in mind this was AFTER sanding it back to re-paint.

    So, does anybody have a similar gun? Any tips on paint thinning and gun adjustment? I want to achieve a fine, but well covering mist as good or better than the pre-packaged paint cans.
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  • #2
    depends on what sort of paint, acrylic, enamel, two pack, they all have different mixing ratios, buy yourself a mixing stick with the paint mixing ratios on it from a automotive paint supplier, or get a viscosity cup and time how long it takes to run through.


    • #3
      Hard to tell, but from that picture it looks like acrylic.

      Many problems with acrylic;

      When thinned too far it runs, when too thick, it splatters.

      Also the acrylic you use is important, the particles in acrylics can be large and clog the nozzle - this may be happening to you. It also dries exttremely fast in the nozzle clogging it up. Residue needs to be cleaned off alll the time - use an acrylic inhibitor which prevents it drying in the nozzle.

      If you can, try increasing the pressure a bit, the nozzle needle should be adjusted before spraying by moving it back to allow a good amount of paint to flow through.
      Also cheap guns can be a real pain to work with. I personally dont like gravity fed guns, i too find it hard to adjust to paint flow required.

      Make sure that the needle and spray attacment are spotlessly clean - any dust or grit will give the results you are finding. Take them out and soak on acetone - this dissolves acrylic particles not just water them down. When you water acrylic down you get water + particles - the particles stay the same size but with more water in the ratio.

      You should be able to run acrylics through a spray gun no problem though. I dont use the funnel test you mentioned - its not perfect. I prefer to mix using a stick, take note of the flow off the stick, it should run freely but not look thin.
      Then i test with the gun, if no go, thin back in the paint holder and try again.
      This is why grav fed guns are a pain - your previous mix stays in the line and can prevent the next mix coming through. Siphon fed guns, you can take the paint holder of easily with no mess and thin back again. try doing that with grav fed!

      Also, make sure you have a GOOD sized compressor - small 2.5hp wont cut it and the flow will judder.
      Supplier of licensed Gottlieb restoration tools.


      • #4
        Wrong paint. Wrong paint. Wrong paint. I think I have mentioned in every build thread that I have done that I use Lacquer. Why are you using House paint?!

        Don't use water based paints. You will never get a good result. I could get a better finish with a foam roller. Acrylic paints need to have stoopid amounts of pressure to come out anywhere near flat. Airless sprayers run @ around 3000psi. You are not painting your house. Whoever told you that you can spray unthinned paint wouldn't know his head from his arse.

        Go and buy some Lacquer (single pack, cellulose) whatever you call it over there. Thin it with up to 80% thinners and then repost the results in this thread. This is the same paint they used to paint your neighbours Valiant and you give some of those old heaps a cut and polish and they will look minty some 38 (odd) years later.

        BTW, I am a painter by trade.


        • #5
          I agree with spacies. Its called Acrylic Lacquer.

          in conjunction with this

          Its used a lot for pc case modding etc. Easiest paint to use and mistakes can be sanded back and sprayed over.

          Man, did you seriously put water thinned paint in your gun?!?

          Arcade joystick is looking great BTW.

          Is that a $20 special from super cheap auto (I saw a nasty logo on the gun).

          Nice gravity fed guns, for home use cost $150 to $200.

          2 guns, one just for primer work and one just for painting.


          • #6
            Yeah you can buy that Septone stuff in standard colours from Supercheap Auto.
            If you want custom colours, then find a paint shop who sells/mixes it.

            Use the budget thinners for cleanup/priming and the good stuff for the top coats.

            Check out the results straight from the gun:

            That machine has not been buffed or clear coated. Nice reflections for lacquer.


            • #7
              I was expecting the comments about Laquer paints (yes spacies, I have noticed ). As I mentioned, I was simply using some primer/sealer/undercoat I already owned, and had used on previous jobs.

              I did get quite good results with the Taxi Cab eventually which was a yellow enamel. Even though I take your point about laquers, I would still expect to get a better result than I was with this gun/compressor, otherwise I wouldn't have bought it and just stuck with the dedicated suction-gun I was already using.

              By the way, this gravity gun was from supercheap yes, but its regular price is $112, as opposed to the $42 for their stock 'suction' gun.

              I can't stand the cleanup of oil based paints, which is why I keep going back to water cleanup.... but I'll admit the Laquer paints sound good. I even tried a spray-can of automotive touch-up paint today (which was a acrylic laquer) and it went on really thick and smooth... I was impressed.

              I assume to use laquer paints, I need an acrylic laquer primer/sealer for the MDF too... is there a particular type I need or do I just walk into an auto shop and ask for a laquer primer?
              My Projects


              • #8
                Try a primer/filler from the gun onto the MDF.

                2-3 coats

                or maybe whiteknight mdf primer first, then 2 coats of primer/filler and then paint.

                try on some scrap and take it from there.


                • #9
                  I agree get some 1K paint (i.e. 1K is normal, 2K is 2 pack paint, with base and hardener)

                  Generally thin it as the manufacturer states, dont think you will need to go to the expense of a visco cup for this application. And some general thinner and you will be set.

                  Once you get it spraying properly just dial it in with the air flow and you will be fine.

                  Oh and if you dont want to polish it at all hit it with some clear once it has flashed off.
                  Last edited by Simon_A; 13th October 2008, 07:28 PM. Reason: Automerged Doublepost


                  • #10
                    Other points.
                    :Compressor to 43PSI" this is not enough.
                    By the time it gets from your air compressor to gun, the pressure will drop.

                    Also very important (well for automotive painting) is water!...
                    Air compressors build up a shit load of heat, moisture in the air evaporates, as the air cools down running out of the line, it condenses in forms water, thus gets in your paint. I've seen it far too often people put the regulators with built in water traps on the compressor, very useless, isn't going to trap any moisture and very inaccurate reading of the air pressure.
                    Personally myself, I run about 5 meters of hose before going to an air trap, then about two more meters before the regulator...

                    Also important is the size of the venturi on your air gun, I think (will have to check) for 2 pac I like about 4mm, and acrylic about 6 mm

                    There is one way to paint house paint through an air gun, that is to heat the buggery out of it, this actually thins it down to paint, still a pain in the ass,,


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