HVLP spray gun in Model Aviation column

Actually, I found the gun at Harbor Freight here in Richardson after I saw the same model at Bill Wilson’s shop. I recommended it to Doug Moon and all the guys on RCOnline. Al Rabe saw our thread and had me pick one up for him when I went over to his house to see his new Mustang. He sent that gun to Frank McMillan. The article followed, obviously, with the Brad Walker reference omitted, of course.

Scott,
Is this unit of the smaller touch-up gun variety in size? Or is it a full size gun? Just wondering is all. How are you mixing your paint? I've found that with HVLP that I'm mixing lots more thinner into the ratio in order to get the material to flow out. I believe this is one of the requirements for a good finish before any buffing/polishing is started. Over on the RCO forum a pro-auto painter vet relates stories of not being able to get as good a finish with HVLP versus siphon feed guns (from the git go, ..there is a learning curve) , perhaps due to the change in technology, and the need to really thin the paint.

I shot clear coats a couple days ago, ..the mixture was over 75% thinners to get the best gloss I've had yet to date. I think I could have gone even higher in the thinner ratio, but kinda liked what I was getting so did not.

What I liked about the HVLP: I was shooting indoors for the first time with the gun, ...no cloud hanging in the air over the subject target (given the relatively "dead air" of indoors), much less over spray (which of course is the design intent).

With the thinner ratio way up, as was my mixture, I was only putting on coats that would end up containing a thickness equal to 25% of the total dope mixture sprayed. This I would think would equal to a very thin coat, all things being normal, as the bulk of the mix flashes off. This would also relate to the lack of material waste which is a big bonus, but I'll be using more thinner stock in stead, as a result of HVLP use.

Given the high ratio mixture I've also found that you need to put on what looks like a very wet coat for best results. I'm still learning here but this is what is working for me. The auto painter vet mentioned above relates that he thinks it's not worth the time trouble or cost of going HVLP given the learning curve, and lack of use the equipment will actually get in the hobby use environment(used once or twice a year depending on build rate). I have to disagree, I think the system is worth using, and learning to use correctly, ..but there is learning to be done.

Also I tip of sorts: Many of us are PAMPA members, and read "Crash Repair" as put together by "Mr Gloss", Windy. I think that he uses siphon feed spray, but am not sure of this (don't recall him saying which system is in use). While taking notes on his technique regarding the use of thinner/dope/retarder mix ratio's in a pervious posting, I noticed that in Stunt News he states a starting mixture ratio of 50/50 dope/thinner, and then adjust from there for best results. I've found currently, as noted above, that this albeit, a starting point is not what I need for HVLP use, ..to even start at. It can be higher on the thinner side to start, then continue to adjust upward for best results. I'm shooting Brodak by the way. It may be a point to include on all finishing discussion in future to include what system is being used, siphon, or HVLP. All mix ratio inf. will be effected by the system in use. I'd not like to try shooting a 70% thinner mixture through a siphon feed gun, ..don't know what the end result would be, runs perhaps?

The gun I'm using looks very much like the one pictured in the link, but mine is a full size auto unit. I've even shot all trim colors with this large gun and like it over the touch-up gun. It can be adjusted down to a very small pattern for trim color work, or opened right up to make quick work of wing panel sized areas.

Sorry this so long (as my post usually seem to be), but enquiring minds want to know. Cheers gents Here's a link to the RCO thread: http://rconline.community.everyone.net/commun_v3/scripts/thread.pl

"No longer in the (overspray) fog."

One thing to keep in mind in all of this is the category of work we intend to do. I would call our hobby work in the one-off custome category--like shooting a show car laquer finish. This is much different than a full blown (pun?) production area where environmental health and throughput considerations are higher priorities than the finish quality. The materials we intend to spray will also imact the type of equipment for an optimum application.

A minor point also, Tony says:

>It may be a point
>to include on all finishing
>discussion in future to include
>what system is being used,
>siphon, or HVLP.
>
>
I sugest this is not the correct classification (or at least may be incomplete. Proper would be to indicate siphon or gravity FEED and then conventional or HVLP for the gun transfer/atomization setup.

My experience is that the air pressure conversion HVLP guns really come into their own when shooting high viscosity epoxies and other materials where higher atomizations arent required. And the air-turbine type HVLP's are extremely good at laquers and thin finishes.

Another thing to be aware of is the air volume reuirement for the conversion-type HVLP guns. My Binks wants 15CFM at 50PSI or so. You gatta have a pretty hefty compressor to keep up with it!

The HVLP's trade-off has been its reduced atomization pressures which reduce the overspray but also increase the droplet size. This is why Tony has had to increase the thinner ratio to get the paint to lay down.

How much retarder are you using?? I've found the Brodak to be very sensitive to the retarder . Without it, the sprayed surface orange peels alot. With it, it works real well--conventional or HVLP.

But 50 bucks is a good deal to play with.

FWIW

What's with the two nozzle sets offered below the spraygun for $25.99 each? Do we need one (which?) or both? I was going to order one, but thought I'd ask first. Scott? Also, it says 15psi and 50cfm, which as Curt stated above, takes a big compressor. I have a 4hp Sears & Sawbucks, which is more than enough. Steve

Randy (who now believe that catalyzed poly-urethane is the only way to paint a plane).

Best, Paul

The top feed is the poop.

Gravity feed makes a lot of sense for a spraygun, fer sure. What pressure and volume ranges constitute true "HVLP". This'n says HVLP, please 'splain. And do we need the extra nozzles or not? A lot of these sprayguns say they are setup for water based paints ...is that lower viscosity or higher, or why does it matter? Rust/corrosion? If anybody knows, please jump in. Steve

The big gun mfgrs responded by "converting" their standard gun designs by using a conversion chamber which drops the 20-40PSI at the inlet to the required low pressure at the nozzle. THis is why you see a small inlet pressure gage on lots of these guns--they are only legal is the inlet pressure is within the specified range.

The real difference in the function of the gun is in its ability to atomize and fan the paint stream. Atomizing pressures in conventional guns, applying a fine finish, are on the order of 30-50 PSI. HVLP nozzle (fan) pressure is 10-15.

It is quite possiple to simply use more pressure than specified at the inlet on an HVLP gun. It will improve the finish quality (better atomization) but with lots more overspray.

In performance measurements, the percent of material transfer to the finished panel is measured--HVLP systems have a transfer efficiency of 90% or better. Standard guns may be as low as 30-50%

Finally, HVLP systems were available in the turbine style like the one described above. (Large inlet size like a small vacuum cleaner hose) These generate true high volume from a blower or turbine source, at relatively high volumes. These are very good systems and have been developed over many years of use i the furniture laquer trade and similar. Campbell Hausfield offers one of these as do others. THis is the "real" HVLP system. The "conversion" style are a different solution to the regulatory issues designed to improve the air quality.

In my experience, the water based materials are higher viscosity than laquers and less than heavy materials like epoxies or latex.

ALL material MUST be adjusted to the proper spray viscosity and shot through a nozzle appropriate for that material. Manufacturers guidelines are best followed here--they have a direct vested interest in getting their material applied with the best finsh.

Hope this helps.

As far as HVLP being confusing. Almost no one uses real HVLP. This version technically is HVLP. Lots of volume with less pressure. The clear I shoot under normal conditions is supposed to be sprayed at 40 psi. It shoots at around 9 psi with this gun and puts out the same amount of volume. That is High Volume Low Pressure if you ask me.

>A minor point also, Tony
>says:
>
>>It may be a point
>>to include on all finishing
>>discussion in future,
>>what system is being used,
>>siphon, or HVLP.

>I sugest this is not the
>correct classification (or at least
>may be incomplete. Proper
>would be to indicate siphon
>or gravity FEED and then
>conventional or HVLP for the
>gun transfer/atomization setup.

CaptCurt,
My thinking exactly!