Reading your info, you appear to have a lot of experience.
What I don't understand is what am I doing wrong if I shoot with shellac
successfully with an hvlp gun. I don't have a problem cleaning.
Just throw alcohol thru, open the valves to throw a lot of alcohol thru
and your done. I don't use brushes to clean, I just run it through. When
I reload it melts any light coating that might be there.

So what am I doing wrong?

On 11/22/2011 2:33 PM, wrote:
On Nov 22, 1:21 am, wrote:
I am admittedly a newbie to HVLP...

I have read that a viscosity cup is useful (if not necessary) in order
to select the right nozzle size and to know how much to thin the liquid
being sprayed.

Googling I saw Ford and Zahn viscosity cups of various sizes... which
left me confused about what type of cup I would want for "run of the
mill" HVLP spraying where I might want to spray anything from shellac to
lacquer to poly (oil or water) to latex paint...

Could someone point me in the direction of what cup (or cups) I might
want to get for such purpose?

Also any recommendations for specific cups or brands?

Thanks!

First, spraying shellac from an HVLP rig is suicide. You can get the
finish out of the gun, but keeping it clean during a shoot and
cleaning it afterward is a huge, time consuming waste. I would look
at a a CAS gun or an old high pressure rig to do that.

Second, there is a lot of information on this group starting years ago
about HVLP spraying, gun set up, etc. You can easily search this
group from he

http://groups.google.com/group/rec.woodworking/topics

I have had several Ford cups, and have never used any of them. Why?
Because every gun shoots differently the way you set up your spray rig
will change that even more. Ford cups are made to provide guidelines
for spraying, not parameters set in stone. The only exception to that
would be folks that shoot high end finishes in a controlled
environment such as upper end car finishers, airplane finishers,
chemical coating specialists, etc. where all other aspects of the
application environment is controlled.

The Ford cup and its brothers are simply one more thing to learn. The
Ford cup only measures viscosity, nothing else. Not one other thing.
So even if you have the material set up right, it won't help you with
how that works with your tip (say a 1.3mm vs. a 1.5mm), your turbine
(if a true HVLP) and how that output works with your gun. It is a
guideline because in HVLP you throw droplets of material thinned for
application, as opposed to material that was marginally thinned and
"atomized" when shot out of a high pressure rig. The Ford cup is an
artifact from a different type of material application.

Your best bet (to me, always) is to buy the finishes you want to learn
to shoot and experiment with your gun and thinning mixtures. Spent
$50 on finish and thinner and mix up some sample batches of finish to
shoot. Record time of day, temp, humidity, and of course, your
mixture. If you have multiple tips, write that down along with the
gun settings. If you are using a CAS gun, then write down the
compressor psi settings at the compressor and at the gun. On my old
Fuji gun it didn't have anything on the fluid knob except the
knurling, so I took a three cornered file an put a notch in the knob
at twelve o'clock for reference. That way I knew exactly what to
record.

After you spray enough, you will pick up the characteristics of the
gun and the materials you shoot and will be able to use the equipment
without too much fuss. So practice, practice, practice.

Most of the time you can get good results right off the bat with
today's finishes. But repeatable, great results are from learning the
craft, no different from learning woodworking or brick laying. You
have to invest the time and money.

Robert