My experience spraying finishes.

[Rob Young]

I got ford #4 cup. Any resources I cold read through how to use it? Well, how to measure is pretty straightforward, but understanding what needle/nozzle combination to use depending on measured viscosity to use is not obvious.

The manual for my HVLP rig has a chart that gives starting points (key thing is starting points!) for #4 cup time and N/N combinations.

I think you mentioned having a Qualspray gun?  That should have a similar table or Jeff Jewitt should have one on his website somewhere.

So from memory, the numbers may not be correct, if a quick test of my finish shows 35 seconds out of the #4 cup I go to my chart and it suggests that the 1.3mm N/N set is good for 30-50 sec then that's what I'll start with.  If I was close to 50, I'd probably thin just a touch rather than move to a larger N/N size.  I don't get hung up on the test temperature except that colder == slower and hotter == faster flow from the cup.  But if the temperature is comfortable for me, it is probably comfortable for the finish formulation and things will be good enough.

And you may have already noticed that not every finish manufacturer gives viscosity in relation to the #4 cup.  There are conversion charts around for the different methods.  Google can cough them up pretty easily.

[Rob Young]

Lol, It was in the book. Right by the warning label "WARNING This book may cause paper cuts. Don't look into the spritzy end of the spray gun"

In my building, there are several labs with rather powerful research lasers.  Somebody had these stickers made up once:



And I just found a few on-demand printing places that sell them.

[jteneyck]

There is a chart on Jeff Jewitt's website showing the recommended needle size for different viscosity finishes.  It's buried in the article on spraying paint, so it's not so obvious.  Here is a link: Link When I used a gravity feed gun, none of the WB finishes I used would spray all that well through a 1.4 mm N/N.  They typically had viscosities in the 50 second range and I had much better results with a 1.8 mm N/N, or I had to add 5 or 6% H2O to lower the viscosity enough to use the 1.4 mm.  But with the pressurized Qualspray gun I now use, I use a 1.0 mm N/N for most all the WB clearcoats I spray.  The finishes atomize so much finer with that arrangement and, as you might expect, the quality of the resultant finish is much higher and easier to achieve.  I'll never go back to a gravity feed gun.  

John  
[url=http://homesteadfinishingproducts.com/wp-content/uploads/2014/05/paintspraying_ver3.pdf][/url]