I often receive inquiries from smaller wood shops looking to purchase a gravity style spray gun for their shop. The first question I ask is whether this will be their primary spray gun.
Gravity guns are recommended all the time in postings, which is why I'm addressing the forum on this subject. In the almost twenty years I've been in the woodworking industry I've worked in a lot of different shop environments and I can not think of many situations where I would recommend a gravity gun as a shop's primary spray system. It wouldn't hurt to have an open conversation addressing the different systems available to help shop owners make the correct choice as to which system best fits their needs.
Gravity guns were designed by the European auto body aftermarket. The benefits of the gravity gun are:
1. Easy cleaning, allowing for quick, easy color changes. In the auto body shop they may be spraying a blue bumper one minute and a red hood the next.
2. Complete atomization. A gravity gun will spray the entire product to the last drop and a bottom feed will not pick up the last bit of paint. Automotive paints are very expensive.
The biggest downside for the cabinet or furniture shop is having the cup on top, making it hard to spray inside a cabinet and/or around and through a chair.
From contributor D:
As the leading proponent of gravity feed guns on this forum I present the following justification for my position.
1) We are in fact talking about a small shop. This, by my definition, is a shop that sprays finishes less than two hours per day when averaged over a week. Obviously, the nature of cabinet and furniture building is that, before you need to finish something, you must first manufacture it. So a small shop would be one that first makes something and then needs to finish it. This is not a continuous production line scenario.
2) If you are in a production situation, a Kremlin Airmix (or equivalent Air Assisted Airless system) is the only way to go. It puts out a lot of material quickly, at low overspray and with fantastic transfer efficiency. Since you just basically put a hose into a can, clean up and catalyzed finishes are less of a hassle than with pressure pot systems, which I consider annoying.
3) Iím biased. Before I started playing with furniture finishing I painted cars, a field in which, as you correctly stated, gravity feed completely rules. I started in auto body with a Binks 7 and then got my first SATA 90 (quite possibly the best high pressure automotive spray gun ever invented), which opened my eyes to the advantages of gravity feed. I went on from there to the SATA nR95 HVLP and now the Nr2000 and RP. Once you see what a SATA can do, itís hard to go back. Spraying silver metallic mica paints on a Mercedes Benz is somewhat more challenging that spraying C-V on a pine door. This I can tell you from direct experience.
Why gravity feed rules:
1) Gravity guns are much better balanced than siphon cup guns. Therefore, they give far less arm fatigue.
2) Clean up is easier than any other system. A big deal if you are using the gun in the manner that I do when finishing, for example, a home entertainment system.
a. Dye stain. (clean gun, 2 oz of lacquer thinner, takes about a minute)
b. Wiping stain. (clean gun, 2 oz of lacquer thinner, another minute)
c. Conversion varnish with maybe two or three refills (clean gun, 2 oz of Xylene, another minute)
This same schedule would require three pressure pot systems or gallons of solvent and about 30 minutes to do the same thing.
3) With catalyzed finishes you can mix up only what you need when you need it. In fact, the plastic cups of many gravity guns are graduated so that you can mix in the catalyst right in the cup and then start spraying. There is no corrosion or gelling in the gun as there can be in pressure pot systems if you donít service them immediately. For polyester or acrylic urethane, this is a fantastic advantage.
4) Refilling the gun takes seconds using a filling station. Place the gun on one of the three hooks. Take off the lid, pour the paint through the strainer in the loop above the gun, put the lid back on and keep on shooting. The entire refilling process takes less than a minute and thatís if I go slowly.
5) The inside of the cabinet problem is valid, but I design my stuff with finishing in mind and donít use tightly spaced fixed shelves. If youíve got three feet, this isnít an issue at all and if you donít, you can always whip out the MiniJet and get into damn near anywhere. Pot guns arenít that good in tight areas either, since you have to drag the hoses around and these, like the gravity gun's cup, can ruin a finish just as easily if they are dragged over it.
The undeniable advantage that pressure feed has over gravity feed comes when using thicker materials. With pressure pots, you can often get by with cranking up the fluid pressure. With gravity, your only solution is to use a larger needle/nozzle setup. This is more expensive that turning up a regulator. My solution to this is to thin everything I spray to the same Ford #4 cup timing. This way, whether I shoot lacquer, pre-cat or C-V, I never have to change my gun settings. I have a separate gun for waterbornes, which has a larger N/N setup than the gun I use for solvent based finishes.
Since they came from the automotive world, where paints can cost a couple of hundred dollars a quart, the top gravity guns are designed to give superb atomization. SATA, DeVilbiss, Iwata and others deliver superb finish quality.
Since I have changed to top cup guns (about 4 years ago), life is much simpler. Since I have changed to Astro top cup guns (about 2 months ago), my finishing is near perfect for my small operation - and so are the results!
It takes me about 15 seconds to add more finish to cup and about 30 seconds to a minute at most to clean gun between coats and after finished and about a cup or two of thinner. Since my time is very precious, as I work mainly alone with a few part-timers and have to do most everything, the savings in finish time is significant.
I think the pressure assist guns like Kremlin are great, but for larger shops than mine. Some of my friends have Kremlin even in small shops and that works fine for them - it's just not for me.
I use these guns to spray everything I do, from large kitchens down. I have spent all day spraying on a large job, but usually spend an hour or less.
I am confident I could gross 3-400k a year using these guns. I am now around $150k and only spray probably 10 hours a month.
If I have to spray larger panels, I just push pressure up to 30 lbs. showing when trigger is pulled - normally I only show 10-15, as I hate overspray.
1. spray on water stain (1 qt cup or 2 gal pressure pot for big job)
2. Graco AA airless i pass vinyl sealer
3. hand sand 320
4. wipe on gilsonite glaze?
5. shading sealer with 1 qt cup (vinyl sealer with Mohawk ultra pen stain, usually)
6. 2nd sealer coat with Graco sprayed right after shading, no waiting necessary
7. hand sand 320
8. touch up any sanded through edges and spray 1st topcoat (10 gal agitated pressure pot - a must if using any topcoat with flatting paste)
9. quick wet sand with abralon and final topcoat
This system has worked best for me over the years and everyone should use what works best for them. Just don't be afraid to try something new. Those gravity feed cups are great - I love the small amount of overspray in the field and have even used my Sata to do kitchen cabinets in a house on a strip and refinish job. (I did the drawers and doors in the shop.)
Here's my present shop situation:
One-man with full time wife as an assistant. Infrequent part time hires.
Spray requirements (from primary to infrequent): Kitchen and bath cabinetry, flat panel stain grade wood finishing in the shop (usually outdoors). Other cabinetry in the home (same as above). Furniture (chairs, tables, etc. for local unfinished furniture business). Job site spraying and touch-up of stain grade cabinets. Job site paint grade spraying of installed new cabinetry. Furniture repair and refinishing (as required in the repair process).
Present spray equipment (in the order purchased). Note: I started 12 years ago building and finishing custom furniture (no cabinets) and evolved into a custom cabinet shop about 8 years ago. I have recently changed to building frameless cabinets and finishing (what needs to be finished) before assembly.
Apollo single stage (3 PSI) turbine and quart cup gun.
Apollo three stage (3, 6, 10 PSI) turbine with quart cup gun.
Wagner Airless sprayer.
Kremlin Air Assisted Airless (Airmix) system with 5 gal pail agitator.
Astro gravity feed 1.3 and 1.7 (2 guns).
Related spray equipment:
Craftsman 3.5 HP, 25 gal. portable compressor.
Porter Cable 7 HP, 80 gal. (upright) stationary compressor, plus 30 amp wiring, permanent air lines and filters, water separators
Here's how I put all these guns to use:
Single stage, 3PSI Apollo: Spraying stains and touchup work with shellacs and NC lacquers.
Three stage, 3-10 PSI Apollo: Same as above but can handle most other (heavier bodied) clear coat finishes with proper tip and PSI setting.
Wagner airless: Oil and latex based paints.
Kremlin airmix: Large volumes of clear coat film finishes.
Astro gravity feed: Post-cat conversion finishes.
Pros and cons of each:
Apollo: Note: The single stage unit was upgraded to the 3 stage unit. Had I bought the 3 stage unit to begin with, I would not have needed the single stage unit.
Pro: No compressor or air line filters/regulators required. No fluid lines. Easy clean up. Easily portable. The 3 stage unit can handle all stains and film finishes with the proper tip/needle and PSI setting. As long as the finish is clean (strained) before putting into cup, there is no chance of contamination as there is with air compressor fed guns.
Con: Atomization of some finishes unacceptable, at least as compared to the Kremlin and Astro systems. Very slow application compared to all other spray systems I've used. Requires more passes than Kremlin and Astro to build finish to desired thickness. Quart cup strains arm and hand on large jobs, aggravated due to slow pace and extra passes required. Overspray considerably greater than Kremlin or Astro. Turbine runs full time. Overspray is considerable compared to Kremlin and Astro.
Wagner Airless: Note: This is a low end sprayer but performs well, but I'd consider a more expensive Titan airless if I did a lot of paint grade work.
Pro: Airless is superior to anything I've tried for applying oil and latex paints. Very fast application. Quick set up. Quiet. Portable. Great for flat panel or unassembled cabinet part spraying, or for large installed, unfinished new construction work.
Con: Long and tedious cleanup required. Overspray can be overwhelming and must be considered more seriously when spraying paints as compared to spraying clear coat film finishes. Because of the fast transfer of paint, this system is the most difficult to apply properly. Runs are almost a given when spraying installed cabinet boxes, so follow-up time must be allowed to correct these defects.
Pro: Quiet. Superior transfer efficiency - overspray is negligible. Superior atomization. Quick and easy cleanup. No cups on gun offers light weight, better access in tight spaces, and no stopping to fill cups. Can spray up, down and sideways with equal ease. Gun is easy to break down when necessary to clean or remove obstructions. Great for large and small jobs that require clear coats.
Cons: Fluid line fills with finish, so a minimum of half a gallon is generally required to do any spraying. Because fluid travels through the fluid line before reaching the gun, pigmented finishes (paints) and stains can be difficult or impossible to clean completely, which leads to contaminating subsequent clear coat finishing. Compressor, air line and associated air line filters and regulators are required. Not as portable as turbines or airless because of compressor requirements.
Pro: Quiet. Superior transfer efficiency - overspray is negligible. Superior atomization. Quick and easy cleanup. Superior flexibility with regard to spraying a variety of stains and film finishes. Superior when required to do very small jobs such as sample blocks or experimenting with finishes. Cup over gun provides better balance and less operator fatigue than cup under gun. Less expensive than other systems which produce comparable results. No fluid lines. More portable than the Kremlin, because there are no pump and fluid lines used.
Con: Compressor, air line and associated air line filters and regulators are required. Cup needs refilling. Cup restricts movement in tight places.
Summary: If you want to have a single system that can do all your stain and clear coat finishing, the Astro system is going to be hard to top, whether you are on a budget or not. Three or four of these guns with different tip/nozzle configurations will do everything I have outlined above very nicely, with the possible exception of spraying latex paints.
All of this in purely my opinion, based on my experiences with these spray systems. The benefits and restrictions of each system must be weighed in view of your finishing requirements and budget, as stated in the beginning. Also keep in mind that some of the items I list as ďconsĒ might easily be listed as ďprosĒ in your particular situation.
Pro: Bleeder type gun, allowing a considerable blast of air to be used to blow off foreign matter from part surface prior to spraying.
Pro: Spray pattern and fluid adjustment allows for spot through full fan spray pattern and full control of fluid amount dispensed from gun.
Pro: Duel trigger allows air to be dispensed (without fluid) with the first stage of the trigger squeeze.
Con: Single stage (fluid only) trigger squeeze.
Pro: Spray pattern and fluid adjustment allows for spot through full fan spray pattern and full control of fluid amount dispensed from gun.
PS - I finally made the change to Duravar last week and am really learning to appreciate the quality and benefits of the easy clean Astro HVLP.
Comment from contributor A:
I'd like to comment on reducing the strain on your wrist, which a number of posts alluded to. If you can spray without having to carry all your material in a cup either over or under the gun, your wrist and shoulder will appreciate it over the long run. Those of you who spend more than a few minutes at a time spraying know the muscle tension and consequent strain you experience. This also contributes to carpal tunnel syndrome. Get rid of the weight of the material and use a lightweight gun for the easiest time in your finishing experience.