Viscosity Cup Questions

[Rich P]

I recently picked up the HF HVLP two gun set and while it comes with suggestions for viscosity it does not come with a cup.

After some poking around on the net, seems there are two common types of cups, Zahn and Ford.. Within these types there are "sizes" which correspond to the relative size of the hole and the viscosity of the material to be sprayed (so it does not take more than a minute or so to empty). The Zahn cups are supposedly much more expensive than the Ford type but I have no idea why. I did find one source that provides a table to cross-reference the readings from the two systems.

Initially I'm going the be spraying oil based enamel.

So,here's the questions:

1. What measurement system does HF use in their guns?

2. Is there any reason why I should spend lots more for the Zahn? (It looks like the Ford #4 is fairly common.)

3. HF does not seem to sell their cup any longer. (The one pic I found here in a post appears to be a Ford-type.) Are there any other good sources for these puppies?

[Rich P]

Since nobody here chimed in I sent an email to HF tech support asking which type of cup I should purchase. Their reply came back as promised within 24 hours. Here it is...

"Any viscosity cup will work for this application."

This was after I had explained that there were different measurement systems based on the type of cup. Meantime I looked at all of their HVLP manuals and the only one that mentioned a measurement system referred to "DIN" and I have seen a DIN cup mentioned somewhere.

I figure at this point I'll pick up the Ford-4 version, get a reading and do a test application...then thin if required, measure again and do another test. Once I get it dialed in I will have a reference point for future applications and have something that will hopefully be repeatable.

[paintandbodtman]

viscosity cup

Most paint manufactures will have a recommended flow rate for their products based on the type of cup used.If you have never used one after added the reducer to your paint you dip the cup in the paint and then start you stop watch as soon as you remove the cup from the paint and stop the watch as soon as the stream of liquid breaks that gives you the flow rate in seconds. Hope this helps


Wayne

[Rich P]

Wayne,

Thanks for the inputs. I actually called a local auto paint store yesterday asking about a cup and their response was "we have not carried those in years...everything is pre-mixed". For someone new to spraying, I can see what folks may get put off. For example, you mention "flow rate" which I guess is the seconds it takes to empty the cup but if one is not in the business it is not clear.

Since I'm not spraying automotive enamel I feel a need to thin my Rusto product down to some viscosity that might work. I found a 4mm "DIN/Zahn/Ford equivalent" cup on eBay for around $10 delivered. All calls to local sources for a cup have come up empty (even SW).

I'll be spraying Rustoleum primer and hammered and will try to post my results for others who might be interested, time permitting. The label info on the Rusto products does not offer much help.

Why can't this be easier? If it were just a sheet rock wall I would say "it's only paint" and can be easily done over but this is enamel on metal and I'd like to get it right the first time.

Rich

[Tom Slick]

could you measure and note the visc. then test to see spray characteristics, adjust then repeat until you get a good spray pattern?
No real need for charts and being scientific. In theory you could drill a hole in a dixie cup, measure the time it takes to empty as a baseline and adjust from there.

I can tell you that the painting dept. where I used to work measured everything by weight or volume. None of the materials were thinned unless they needed to change the flash time. In fact most materials specifically recommended against it.

[Rich P]

Tom,

I thought about your dixie cup suggestion and decided that for $10 I'd spring for the real thing. Hopefully it will be easy to clean and last for a while. The Rusto hammered product specifically mentions thinning for spraying which is one reason I'm gnawing on this bone. OTOH it also says it can be brushed, but where's the fun in that!

Rich

[master53yoda]

here is a site that has cups available.
http://www.finishsystems.com/fordzahncups.html


I bought a small plastic funnel that holds about 3 ounces and installed a brass nut with a 3/16 hole drilled in it in the tube. the funnel works better then a flat bottom cup would because of the taper of the bottom of the container. I used Tom's method to get a calibration for my guns. also the thinning requirement is not the same for the gun and the paint pot that i have. the pot has to be a little thinner to get good coverage.

the difference between the ford and the other cups has to do with the smoothness of the cup walls and the accuracy of the orfices. In laboratory use the need for accuracy is far greater then what we would ever see in painting and the cups used are far more consistant one to the other.