Viscosity Cups? Swing, Nailshooter?

While we're on the subject.... do you guys use the viscosity cups that come with HVLP guns? Do you know of a good resource explaining their proper use? Many of the sources I've seen on the internet contradicts one another (big surprise!).
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
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On 2/9/2013 11:29 AM, -MIKE- wrote:

I know how to use one, yes ... but I think it may depend upon the cup that is usually provided with the HVLP spray unit, and the particular viscosity table for that cup, which should be in the manual.
I simply dip mine into the product, while still in the can, until full, lift out and count the seconds until emptied.
Mine is calibrated to my unit thusly:
Water Based Paints/Latex: 25 - 60 seconds Oil based paints: 45-50 seconds Primers: 45 - 50 seconds
Also mine holds exactly 1/10th of a liter, so when I need to thin to 10%, 20%, etc. with a product, I have an excellent chance of being close enough, even with a quart.
Simply hold your finger over the bottom of the cup and fill it with thinner of choice to full for 1/10, etc.
Does your manufacturer have a website?
--
eWoodShop: www.eWoodShop.com
Wood Shop: www.e-WoodShop.net
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On 2/9/13 12:16 PM, Swingman wrote:

This is the one Rockler sells... which is the same exact one HF sells, in a different box. http://www.rockler.com/product.cfm?page 469 Yes, I know your Earlex would be a big upgrade. :-)
The manual (on the site for download) says to time until "the first time the fluid stream breaks (not how long it takes to drain the cup entirely)." And it also says the "time for fluid flow is between 8-20 seconds" which sounds odd to me.
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-MIKE-

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Lab grade cup and its proper use:

http://www.youtube.com/watch?v=LJDmQt_xpco

<<Reality is sentence #3>>, starting with "However":
http://en.wikipedia.org/wiki/Ford_viscosity_cup
As I understand it (take that for what it is worth) the Ford Cup was developed by Ford auto engineers in the 30s to assure that their black paint was the right viscosity for their cranky spray machines. They were able to use and batch paint correctly with this simple system as they kept all the note required to record successful spray days that also recorded the existing environment conditions at the time of spraying.
For me, they are a waste of time. ALL approximations used in viscosity cup recommendations are given based on results from lab tests. When will it be a perfect 77 degrees with 33% humidity where you live? Conditions at the time of application never match the data given by the manufacturer, and with temperature being the most influential, their data is of no use.
Many years ago I had this discussion with a paint rep that came out to inspect a finish I had applied. He wanted to know if I had used the cup to determine viscosity. His application data showed all measurements for proper viscosity taken at 77 degrees. During the summer, it may only get down to the upper 80s here, ten degrees hotter than the data sheet, and by noon it is in the low/mid 90s. These temperatures rendered his viscosity tests irrelevant. I sent him packing and got the industrial rep out there and we resolved the problem.
So the point of all that is that temps are the biggest problem for any sprayer. And they are at any time since they affect the viscosity of the materials so much.
A viscosity cup can get you in the ballpark to get going and they are good for that, sometimes when it is cold. If you are spraying at 55 degrees, it is easy to over thin to get the material out of the gun. A viscosity cup is good for that. But past about 65 or so, I wouldn't think of using one. Mix, spray, test on scrap. Record results so next time you will have them at hand.
Since your equipment can be a factor as well, you have remember that, too. Do you have the same tip size on your gun that they used when determining recommended viscosity? Are you using the same air pressure? Are you using a device to remove moisture from the air (a must here with our super high humidity) before it hits the gun? All of those things factor in, and unless your spray equipment is the same as the test equipment used by the manufacturer, you results won't be optimal.
So, after all of that.... find a product line you like that suits your needs and stick with it to learn it. Then mix, spray, test on scrap. Record results so next time you will have them at hand. As I told Karl before he started his plaque, with an unfamiliar product I would buy two quarts of product. One to mix up and test my setup with, and one to open as pristine to mix for finishing. No viscosity cup can match an actual test shot.
Probably a lot more than you ever wanted to know.
Robert
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On 2/9/13 1:07 PM, snipped-for-privacy@aol.com wrote:

Not at all. Thanks for taking the time to present such a thorough opinion.
--

-MIKE-

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