I'm about to have a go using the gelcoat cup gun for the first time and was wondering where it start with the flow adjustment screw.

I've been doing some "dry" runs just blowing air through it and calculating an appropriate cfm from the compressor pressure drop. I looks like approx 1/4 to 1/3 open would give the specified 5.8cpm @ 80psi.

Is this typical of what others are setting the adjustment screw at?

Any advice would be much appreciated.

There are quite a few variables to deal with so its difficult to give exact settings as much will depend on your compressor and the viscosity of the gelcoat you are using but these are the settings I find work best for me when using GC50.

With the gun assembled but empty and the air flow screw half open fully depress the trigger and set the regulator on the compressor to about 55 psi.
You can now add some gelcoat and fine tune the spray pattern using the adjustment screw on the gun.

The way you spray differs greatly from a conventional spray gun. Hold the gun a good 18" 24" away from the part. Make sure you start spraying with the gun aimed away from the part and feed onto the part, this way you will avoid big blobs of gel on the part as the medium starts to flow. The same applies for when you stop spraying, release the trigger with the gun aimed off the part. Once you start spraying avoid stop/starts as this will again cause blobs to drop on the part.

I would suggest some practice runs. Spraying onto a piece of glass works well and you can practice laying the gelcoat down evenly, ideally 0.2-0.4mm thick. If your using GC50 you have the advantage that it will set hard unlike conventional gelcoats, that way once cured you can peel it of the glass and measure the thickness with a vernier/micrometer.

Hope that helps Warren.

Carbon Copies Ltd

Hi Warren,

Many thanks for all the info. It gives me a very good starting point.

Neil.