Popular Woodworking – August 2019

58 ■ POPULAR WOODWORKING

Flexner on Finishing

PH

OT

OS

BY

TH

E^ A

UT

HO

R

A spray gun is a tool that turns

a stain, paint, fi nish or other liquid

material into a fi ne mist—a process

called “atomization.” It then propels

the liquid onto a work object. Spray

guns vary in type and quality, but

each is designed to produce the fi nest

atomization possible for the money

in order to create a minimum of or-

ange peel (a three-dimensional eff ect

caused by the fi ne mist not totally

fl attening out on the surface).

All spray guns will spray all stains,

paints and fi nishes, and all stains,

paints and fi nishes can be sprayed

through all spray guns. The quality of

atomization produced by any spray

gun can be improved up to the capa-

ble limit of that gun by increasing air

pressure, thinning the liquid, or both.

(It takes less air pressure to atomize

a thin liquid and more air pressure to

atomize a thick liquid.) Generally, the

more expensive the gun within each

spray-gun type, the better the gun is

capable of atomizing.

Compared to rags and brushes

(the other common tools used to

apply stains, paints and fi nishes),

spray guns transfer the liquid faster

and leave a more level surface, but

they cost a lot more and create more

waste because of overspray and

bounce back (the spray bouncing

back off the surface). This waste has

to be exhausted for health reasons

and to keep it from settling back on

the work. The equipment for accom-

plishing this adds to the cost.

Nevertheless, the increase in

speed and degree of levelness make

a spray gun an essential tool for pro-

duction situations and a defi nite aid

in non-production situations.

Compressor or Turbine

There are fi ve large categories of

spray guns:

1. Conventional—operated off of
   compressed air from a compressor.


2. Conversion HVLP—operated off of
   compressed air from a compressor.


3. Turbine HVLP—operated off of
   air from a turbine.


4. Airless—operated off of a high-
   pressure pump.


5. Air-assisted airless—operated
   off of both compressed air and a
   high-pressure pump, it produces
   a more orange-peel-free surface
   than the airless alone.

1

2

3

4

Spray Gun Basics

By Bob Flexner

How to choose a spray gun.

2-4 The three primary spray-gun

confi gurations are a cup under

the gun, a cup on top of the gun

and a separate pressure pot that’s

attached to the gun by a hose. The

fi rst and second confi gurations can

be powered by a compressor or a

turbine. The pressure pot for the

third has to be powered by com-

pressed air.

1 The two primary sources of air

for a spray gun are a compressor

and a turbine. Besides size, the key

difference is how much air pressure

each produces.