Thought I would do a how too. Awhile back bow bender (Royce) was lamenting the lack of how to resources.That and there always seem to be finishing questions hoping up here on the bench, so here ya go. But it seems us mortals cannot start a thread in the how to forum or even post replies? Heck, I even PMed Terry Green to ask him about it, but he blocked my message. Second time I’ve been dissed lately! Oh well the next best place is the Bowyers Bench, we are the ones making stuff, right?
So this is a thread on how to get set up for spraying finish, not the actual spraying technique. Might have a few tips on spraying, but honestly if you want to learn the movements involved in spraying, watch videos of robotic arms spraying Ferrari’s till your eyes bleed. Its about consistency and nothing is more consistent than a robot. The apex painters in human form are the folks doing custom Auto painting.
So for those of you who are not currently spraying finish, but are thinking about it, this thread is for you. If you are happy with your current method, good on you. If you are thinking about a more professional finish for bows that might be marketed, hopefully this will help.
I make no claims to being a painting guru. I mostly learned in a vacuum, so most of my knowledge was acquired by trial and error. You don’t want to hire me to paint your Tesla. I know there are better, more experienced painters than me on this forum, so please feel free to add to or correct anything you see written here.
First thing to consider is the type of spray setup that will suit your needs. There are a few options.
The most common is an air compressor. A compressor setup is probably the least expensive and most versatile outfit. Everybody has a compressor, right?
The next most used setup is an HVLP turbine.
Another option is an Airless or Air assisted airless sprayer.
I'm not going to go into rattle cans or Preval. Nothing wrong with them, just not the level of finishing we are trying to achieve.
So the biggest thing we are striving for is an even, smooth layer of liquid plastic on our carefully crafted masterpieces. The way to achieve that is thru atomization. For that we need adequate pressure at the tip of the spray gun.
An HVLP turbine is rated in stages, which is the number of fans it has pushing air. The more stages, the more air pushed and more pressure at the tip. A common 3 stage turbine will get you a real world rating of 3-5psi, a 4 stage might get you close to 8-9psi and a 5 stage will get you over 10psi. They start getting expensive over three stages. If you don't get close to 10psi, you are going to need to substantially thin out your finish or its not going atomize well and you will likely spend more time than necessary sanding or rubbing out your efforts.
Tip#1 If you want an HVLP setup its easy to build one yourself. The turbine is nothing more than a vacuum motor and garden hose fittings.
This is a 3 stage motor. You can see the 3 segment at the bottom are the fans. Two and 3 stage vac motors can be had cheap if you shop around. Four and 5 stage start getting real expensive!
Here is my recommendation, buy (2) two stage or three stage motors and hook them up in series. You won't get an increase in air flow, but you will get an increase in pressure. Make yourself a plywood enclosure, because the enclosures that come with manufactured units are too small and not adequately filtered. Plus they are way loud! A homemade 4 stage box with some insulation on all sides and a HEPA furnace filter works better than almost any stock unit and might set you back $150. A manufactured 4 stage is upwards of $1000. Save your money for a good gun. You will need 20-30' of tubing, any longer and you get too much pressure drop. You don't have to buy turbine hose, HVLP's use garden hose fittings so any light, flexible tubing that you can mount hose fitting too will be fine. There are lots of good turbine guns out there. Gravity feed is superior to pressure cup, in fact a pressure cup with HVLP is almost an oxymoron.
You don't need a monster gun with a quart cup, 4oz cup is plenty big unless you are spraying many bows at once. More on guns later.
There are some cons to the HVLP. All those impellers generate air friction and the air delivered to the gun can be quite warm. On a hot day your finish can dry in the air on the way to the bow, leaving a sandy finish. Another issue is high humidity. There is no way to inline filter with an HVLP, they rely on high flow to generate pressure. If you are in a high humidity area, its possible to get fish eyes or orange peel effect when that warm moist finish hits the cooler work surface. There are reducers to slow dry time and other additives for almost any condition, but I think less is better in this case. If I can shoot at package consistency, I’m happy not to fuss with it.
Also since hose length is limited, you will have your turbine nearby, which sucks because the are really loud, they can stir up any dust lurking around and can suck overspray back into themselves if the filtration isn’t good. The biggest advantage of the HVLP is transfer efficiency. Low pressure equals less overspray, which could be important if you are spraying $700@ gal. Auto clears like Travis (4point) but if you are only catalyzing 2oz for one bow its a non issue. I have never used a LVLP or mini gun with an HVLP turbine, could be a hot ticket.
All that said, I’ve sprayed a lot of woodwork with an HVLP and there is no reason a person can’t get an excellent finish using one with a high quality gun.
The air compressor setup is the tried and true spray persons outfit. You will never starve for atomizing pressure. You can spend a lot of money on a really nice 80gal intercooler compressor, a SATAjet Phaser gun, an industrial oil/water separator and all kinds of fancy fittings, but if your not shooting Maserati’s, thats not required. Lots of good examples of folks painting setups to be seen with some searching. I’m going to show mine as an example of what can be cobbled together on the cheap, but can still be highly functional.
This is a compressor I picked up free on C-list. The guy did not want to replace the piston, so he bought a new one. I’m always happy to take advantage of our throw away culture. I wired the pigtail plug into the pressure switch, so when the compressor kicks on it powers up a 12v bench supply (salvaged, modified ATX power supply from a junk PC), which turns on the cooling fan attached to an A/C condenser, both scrap from a Toyota. See the trend here?
You can get by with a smaller compressor, but its a good idea to check the SCFM rating at the pressure needed for your gun to make sure there is enough air capacity so the compressor won’t kick on during the time needed to spray your project. You can also connect multiple small compressors in parallel to get more capacity if you need that versatility. Just need a T fitting, a couple of check valves and it helps to slightly stagger the cut in/out pressure of the compressors.
Same rules apply here as with HVLP. We want cool, dry, filtered air. After the air has left the condenser, its hopefully cooled a little and when it hits the PVC precipitation pipe the water vapor will condense and there will be little moisture left when it gets to the repurposed water filter housing filled with silica gel beads. The last defense for crap in the air is 2 layers of P95 filter material in the exhaust side of the filter housing.
If you happen to have a real compressor and are crazy enough to use a setup like this, you would want to substitute Zeolite for the silica because of the oil factor. In fact when I replace the silica, I will definitely switch to Zeolite. Interesting material, that can be had cheap in the form of cat litter.
Before anyone flames me for using PVC and polycarbonate, 2” sch40 PVC is pressure rated for 280psi. Even after its been de-rated for temperature, it’s still rated for near 200psi working pressure. I have 75psi safety valve plumbed into the pipe. I don’t need more than 50psi for any of my guns. I would not necessarily recommend anybody use plastic for pressure, but I’m not worried about getting maimed by plastic shrapnel.
That leaves the Airless pump.
Nothing can come close to the pressure generated here, up to 3000psi! It will atomize tar. It will also make a huge cloud of finish. It’s also not practical, you would need to catalyze a quart of finish just to fill the pump and hoses. Which is too bad , because with the correct tip, you can lay down some glass. Still, its an option if you have 50 or more bows to spray.
I know that was long winded. Its even more ovbious this thread does not belong here now. Looks like this will be home for now. Hopefully I imparted some useful info and I trust if someone has something to add they will do so. I’ll try to do the subject of Spray Guns justice next installment.
Topic: How Too.....mostly (Read 4478 times)
