primer generally sprays well through a 1.7-1.8 tip size. A high build
primer needs to be sprayed through a 2.0 tip size. Primers can be
thinned with urethane-grade reducer, but adding too much reducer cuts
the film build. If it becomes necessary to add a lot of reducer to get the
primer through the gun, then it is time for a larger tip size.
Color is less sensitive to tip size than primer, but it is still important.
Most vehicle projects get painted with base coat/clear coat or single-
stage urethane (there’s not much enamel out there any more). Most
urethane colors will work well in the 1.3 to 1.5 tip size range with a
little adjustment to the rate of reduction. There is some difference of
opinion on tip sizes for various clear coats. Since viscosity of clear tends
to have a pretty wide range, there can be some trial and error involved.
That being said, a 1.3 or 1.4 tip size is a good starting point to get the
best atomization. Many clear manufacturers have tip size
recommendations right on the product.
The most common paint guns are gravity feed (cup on top) and siphon
feed (cup on bottom). Pressure-pot paint guns are less common, but still
have their uses. Gravity-feed guns come in regular and HVLP (high
volume, low pressure) styles. With HVLP guns, the reference to high
volume is serious. These guns can shoot some serious cubic feet per
minute (12-16 CFM).
This is an old Sharpe siphon-feed
gun based on the famous “Binks #7” design. It is fairly easy to
service, but part kits for these styles are growing less common.