MIMF

So after my great success spraying clear base coats, and spraying a test of quite lightly dyed colour (in WB polyurethane), I tried to spray full strength colour today. Again a dismal performance. Spitting and uneven spray pattern no matter what I tried. I did manage to determine that adding a 30:1 ratio of dye as recommended actually measurably increased the viscosity of the finish, to the point where it would not drain through my filter paper while the clear and lightly dyed finish would without problems. So, a two step process to move forward. One is I got some distilled water to use to thin the finish, if I continue to have issues. Apparently too thick a liquid is first on the spitting list of things to fix. Second, I got fed up trying to make a $30 Harbour Freight touch up gun work, and I went out and got a new spray gun. It is a Devilbliss SRi Pro finishing gun, with a 1.0mm nozzle and two different air caps. One is called a HS1-K HVPL cap, and one is called a TS1 Trans Tech cap. Apparently the Trans Tech is a newer version of HVLP called MVLP (medium volume low pressure), is more efficient and most people seem to like it, so we will see what we will see. It also came with a whole kit of Dekups System paint cups, with three different filters and all sorts of stuff, so that looks pretty useful. It was a useful sum of money, too, though... I had better sell this guitar...

I never place any finish in my spray gun without running it through a paint filter. You can get cheap paper paint filters at any paint store. This will totally eliminate the kind of problems you are having. Also, it sounds like you are adding way too much dye. The color coats should appear in the mixing jar like ice tea, in regards to the amount of dye. This will allow you to build up the desired color over several coats which gives a more even appearance, and less chance of applying too much, which will happen to you before you learn this skill. Take most recommendations from finishing manufacturers, paint supply salesmen, and spray painters with a healthy grain of salt. They know little about the methods that work well for guitar finishes and they will often steer you down blind alleys.

Thanks for your continued support and advice. I'm going to have another shot tomorrow, and taking all the advice to heart. I will probably start with a reduced mix of dye, since that helped my previous test, but the instructions I am following are pretty specific to guitar finishing (from the stewmac pages, etc.) but I have to learn now to make it work. So far I have just ruined a whole bunch of test paper, no guitar parts... I may also experiment with thinning a bit. Doing things perfect the first time (or the tenth time) is more fun, but getting it right in the end is the goal...

I am assuming your air supply is very clean also Brian. I run my air supply through about 20 ft. of pipe, with 2 moisture traps in that span.
I then have a filter in the supply line, just before a pressure regulator.

Make sure your pressure is where it should be for your gun.

Is the dye/stain you are using a powder, or liquid?

It is the same stuff as LMI Trans-Tint or Stew-Mac Colortone. I think I am past the dye-mixing issue. My air supply has two filters and moisture traps also, and a wet tank/dry tank combination. I am starting to believe I have a more fundamental problem, and I have a day of just playing with the gun and wasting finish planned. I think I have been leaning too hard on my car painting experience - different gun, different finish, different pressures and different coverage needed. I am instinctively going for a wet coat, and I think that is where I am screwing up. I am going to go back to starting from scratch, like I did 20 years ago.

I am starting to think I can indeed make all the mistakes all by myself!

It sounds like your air supply is fine.
Pressure and feed rate are factors that differ with different products.
I don't know anything about the Minwax product you are spraying, so that is not something I can help you with.
I do know that I have tried a few other WB lacquers that I could not spray.
One of them always had tiny bubbles in the coat, whether the pressure was high or low. The other wouldn't atomize well; it came out in a stringy mess, even with higher pressures.

The balance with pressure for me, is to get atomization without being too fine. Too fine, and the lacquer is almost dry when it hits the surface.
If you have sprayed cars, I'm sure you know this.

I think I am going to order a quart of the Brite-tone from Wood essense. You have had success with it, correct? How would you characterize it's spraying behaviour?

I found it a bit different again from the EM-6000 I was using.
I followed the directions on the container, and it worked really well.

As I said in your other post, it does not need as many coats as the EM-6000.
I was spraying 10-12 coats of the EM.

The Britetone took about 7 or 8 coats, as it does build faster.
I'm just about done finishing the wooden pickup rings on a guitar I used the it on, and when I'm done installing the electronics I will post some pics.

You DO want a wet coat. Anything less will result in a cloudy finish composed of dried mini droplets of finish bonded together.

I have given up with the Minwax poly and have ordered a quart of Brite-tone. If I spray a second or third coat of the Minwax wet, it almost splits as it hits the surface, it looks for all the world like water on a waxed car. If I spray it very light, it dries very rough and dusty. I have tried the full range of air pressures and volumes that this gun can do. The brite-tone is what Gordon is using, and is specifically designed for finishing instruments. It's made by the same people who make Crystalac shellac. I'll use the Minwax to finish a floor so I can walk on it with dirty boots...

Some WBs benefit from being thinned with methanol/ethanol rather and water and some might need a retarder to get them to flow out correctly. It sounds like your tint isn't entirely miscible in the finish hence the thickening action.

I don't think of Minwax as being a spraying type of paint manufacturer. They mostly specialize in wipe-on finishes. Their oil stains are great.

If you could handle nitrocellulose lacquer, that is where I would steer you. It is old school and toxic as hell, but it sprays like a dream.