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?
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 here:
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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.
Shellac's about all I spray, and always with an HVLP rig.
Until a year ago with an el cheapo ($150) Campbell-Hausfeld rig; now with an Earlex 5000 SprayStation ... still mid-level or below.
I usw two cups: one filled with the shellac cut I'm spraying; the other filled with alcohol for gun storage between coats.
Between coats I simply switch cups, slosh the alcohol around good and spray some through the gun. When I'm ready for the next coat, I simply switch out the cups.
The only time I contemplate suicide is during the sanding leading up to breaking out the spray unit ... and even that has subdued somewhat with my Festool sanders/vac combo.
I tried spraying shellac out of my Fuji four stage, and about halfway through a large kitchen of cabinets I had large icicle looking things coming out from around the fluid passage, just around the super fine air holes. I had been spraying for about 20 minutes straight and shot about quart and a half of material. I got splatter. I got pissed off.
I stopped, cleaned the gun, and it did the same thing. I had it on low pressure, and was spraying straight sanding sealer, so I the viscosity wasn't a problem. Someway, between me and my setup the shellac fired off too fast. I can't seem to get the mix right for my HVLP, and actually, not even close.
It is exasperating, since I can easily spray BIN which is no more than a pigmented shellac. A call to the manufacturer of BIN was no help; they told me they had "proprietary conditioners" in the BIN mix that allowed me to spray it so easily. What makes that more maddening is that Zinsser makes both the shellac and BIN and they still couldn't help me.
Oddly, I can easily shoot shellac out of a CAS gun, including when mixed down to sanding sealer cut, so I don't worry about it. But out of a true HVLP, it's voodoo to me.
Now that sounds really simple. Suspiciously simple. Any offerings to those Cajun folks in your heritage... maybe a chant or two you aren't sharing? =3D^0
If you would indulge me, how big are your spray projects? Are you spraying out enough material all at once to dump the gun? How big is your cup? What size air cap are you using, and what cut do you shoot? IIRC, the Earlex is a two stage unit, no? Are you controlling the air flow or are you wide out?
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 do> >> I am admittedly a newbie to HVLP...
Obviously, if it all works for you, nothing. End results of finishing are subjective, and if you are happy with your results and method of application, don't change anything.
FOR ME, shellac didn't get it done. I am not sure if I spray too long (literally spraying out a quart cup before stopping), or of when spraying cabinets the blowback didn't contribute to my unsuccessful attempts. Maybe it was all of that.
I did that when I thought priming was necessary. Now I spot prime only, and use the finish material as a primer and top coat as recommended by better finishers than me. No problems since.
That doesn't mean I am not still puzzled and annoyed by my lack of ability to solve the problem. To me, I should be able to spray a solid 30 minutes and blow out a couple of quarts before I have to worry about any material's behavior.
I have seen Karl's work ( da Swinger ) up close and personal, and his quality of work and and scope of projects are just about as good as it gets. He is the shellac master, no doubt. His projects (and Leon's too, by the way) tell their own story of their mastery of wood craft and finishing. Karl has long been a fan of bug spit, way back to O'Deen's days here.
But, me and shellac don't see eye to eye anyway. I tend to think in commercial terms, and that means hard finishes that don't need any kind of maintenance. Shellac isn't abrasion resistant, is provides no color protection, it isn't cleanable except with a damp rag, it isn't heat resistant, and provides little water resistance.
While many tout its ability for easy repair if damaged, it won't be so easy if you are using a tinted shellac, shellac that is naturally colored (orange, amber, etc.) or shellac over stain. Shellac will bond with the stain in most cases, and pull up the color with the finish. Good luck matching that! Of course, clear shellac is a snap to repair unless it is on some old antique which you shouldn't be refinishing anyway.
Seriously, there aren't many hard fast rules to finishing. I have said it before and will repeat it, most folks learn finishing by folklore. They will try something traded in idle conversation with someone at Woodcraft on a Saturday sale before they will sit down and research out the process for themselves.
So if your processes and materials are working and you like your end result, don't change. You have reached the goal!
Not all that big ... this is about as big as they get:
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furniture sized projects ... I leave the kitchens, and most of the client's who want a lacquer finish, to the pro's ... but I do spray all my personal projects.
What size air cap are you using, and what cut do you
I generally shoot shellac with 2.0mm air cap and a 1 1/2 -2# cut, but don't get real fussy measuring.
I do get fussy about the humidity and which alcohol I'm using when it's high (99% isopropyl), otherwise I just use denatured from the Borg.
IIRC, the Earlex is a two stage unit, no? Are you controlling
Just turn her on let'r rip.
When it comes to spray finishing I operate on the "ignorance is bliss" principle (the less I know the less I have to fuss with settings and the less I'm befuddled) ... I turn it on, adjust for the pattern I want, adjust the material flow and distance (on a piece of scrap) to my suiting, and wave away (using my politically correct, well practiced waving method, which apparently also has the pope's blessing because it comes out good ... AAMOF, I no longer feel I need to say a rosary before pulling the trigger!)
Dood!, I'm a simple man ... no complications please!
I do agree if it works you have reached your result. I think you missed one of the amazing things about Shellac. It pops the wood. Better than most other forms of finish. BTW I also french polish, so I am not limited to spraying it. I love it for its ease of use, no VOCs.
I don't know if you are still following this Karl, but I have been away on bidness that couldn't wait. So.... a 2mm aircap, eh? The one specified for latex, and heavy paints? I would never have tried that. Literally, never. Sometimes I do great thinking out of the box, and as in this example, I just don't.
Sometimes, that's the best way.
I always like the process to be as simple as possible. That's why I try new finishes. The easier the application and more dependable the outcome is for me determines if I will learn to use it.
Indeed... I have seen the work. Excellent work, excellent finish on it.
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