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Choosing HVLP Needle Size

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Forum topic by Ripthorn posted 06-06-2011 02:06 AM 5740 views 1 time favorited 6 replies Add to Favorites Watch
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Ripthorn

799 posts in 1738 days


06-06-2011 02:06 AM

Topic tags/keywords: hvlp spray spraying finishing

I got a turbine-driven HVLP spray gun a while ago and have started my first real finish job with it. I am currently using Emtech EM6000 from target coatings (waterbase lacquer), but I was wondering, what relationship should there be between finish viscosity and tip size. This lacquer is relatively thin compared to other finishes. I thought that you used a smaller tip for thicker finishes to produce a finer atomization, so I have tried the two larger tips so far (only that many coats) and found that each have laid down too much material (orange peel city) even with the spray control set very low. Am I totally missing the mark here? Should I be using my smallest tip? I was making relatively quick passes, so I don’t think that’s an issue. Any experts out there care to chime in?

-- Brian T. - Exact science is not an exact science


6 replies so far

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PurpLev

8476 posts in 2402 days


#1 posted 06-06-2011 02:10 AM

thinner material = smaller needle size.
thicker material = larger needle size (otherwise the material will be too thick to pass through)

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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DLCW

530 posts in 1408 days


#2 posted 06-09-2011 05:53 AM

I tried that same finish a few years ago and found it to be REALLY sensitive to temperature and humidity. It didn’t matter what tip I used in my turbine sprayer. I either ended up with orange peel or fish eye. I went through the whole process of cleaning and prepping and couldn’t get the finish to cooperate. Talked for a while with a tech rep and still had problems. I finally sanded it all off, got some precat lacquer, shot it on and got a perfect finish first time. Now I use ML Campbell conversion varnish and get really good, durable finishes every time.

-- Don, Diamond Lake Custom Woodworks - http://www.dlwoodworks.com - "If you make something idiot proof, all they do is make a better idiot"

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Earlextech

1024 posts in 1444 days


#3 posted 06-09-2011 12:24 PM

Tip size with HVLP does not relate to material thickness. It relates more to the type of finish you want. If I am painting I use a 2mm. If I am finishing I use a 1.5mm (even if I’m finishing with paint!). Very simple.

All materials sprayed through HVLP should have the consistancy of cream (for your coffee). Remember it’s low pressure, you can’t push really thick materials through HVLP even with the biggest needle.

Don’t confuse the old fashioned high pressure systems with HVLP. With high pressure everything will go through, then you change the needle to accomadate the thicker material.

-- Sam Hamory - The project is never finished until its "finished"!

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MarcusM

36 posts in 1734 days


#4 posted 06-09-2011 01:58 PM

Sam. that’s interesting; would you say that also applies to compressor driven HVLP guns?

Thanks, Mark.

-- Tilbilly Mark

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Earlextech

1024 posts in 1444 days


#5 posted 06-09-2011 02:14 PM

I personally don’t like conversion systems but, yes, if you are spraying at 10 psi or lower it isn’t really about adjusting the needle size, it’s about thinning to the proper consistancy.

A typical two stage turbine produces about 2 psi. Granted, a bigger opening (say 3mm) will allow thicker fluid to pass through, but it won’t atomize it properly. The consistancy of any material flowing through an HVLP gun needs to be that of ‘heavy cream’ and it will atomize. Then you can use the needle size to create the best atomization size for the job at hand.

Remember the important number with HVLP is cfm.

-- Sam Hamory - The project is never finished until its "finished"!

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KnotWright

247 posts in 2241 days


#6 posted 06-09-2011 03:05 PM

If you finish is “orange peeling” it could be that its not getting enough time to flatten out before it drys. In either low humidity, or high temperatures water based finished will dry out faster and cause orange peeling. I have never tried this product in a latex varnish but might be worth a shot. It does a great job with latex paint in helping them lay flat and gives you a little more open time.

http://www.flood.com/paint-additive-solutions/products/view-product.jsp?productId=12

I have not tried water based lacquer, although I do spray a large amount of waterbourne polyurethane varnish using a compressor driven HVLP sprayer. It tends to lay flat without any orange peeling problems.

-- James

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