Paint Sprayer

Copyright 1995 E.M.(Ted) Edwards


Making the Gun

The circular part shown at the bottom of the drawing is the base to which the jar lid is fastened (see photos). I suggest making an extra one of mild steel to use as a drill guide for jar lids. Size the three holes shown as being threaded on the drawing to clearance diameter. This guide can then be used with transfer punches to mark the hole centers in the SS base. Drill and tap the SS part. Make the rest of the SS parts and weld/braze/silver-solder them together. Be carefull about spacing and alignment. You could use something other than stainless steel but I felt it would stand up better to various base paints.

Make the remaining parts as per the drawing. Note that two sizes are shown for the hole in the paint nozzle. Originally, I made the unit with the smaller hole. I made a second nozzle with the larger hole to spray some particularly heavy paint that was not supposed to be thinned. I've been using this one since. I can't make up my mind whether this gives a poorer surface or not. It sure can move paint!

No trigger valve is shown on the drawing .. Buy a small air blow gun (I got mine surplus for $0.50) and a 1/8" pipe to tubing adapter. The tubing end of the adapter should fit the nozzle end of the blow gun - you don't need the nozzle. The 1/8" NPT end screws into the back end of the sprayer air tube. This is a heck of a lot less work than making a trigger valve!

The paint nozzle is adjusted up or down as needed (more later) so a compression spring is slipped over the paint tube between the lock nut and the washer under the nozzle. This spring is not critical - its purpose is to keep the nozzle from turning when the gun is in use. I made the nozzles from round brass rod and cut the hexes with a spin index and the mill. If you don't have a mill, you could just knurl them on the lathe. Hex is better since the air nozzle should be properly tightened. I'll mention the paint nozzle again later.

The paint container is a glass jar. Choose one that is a size from some product you use quite a bit so you can aquire a number of empties. Take one jar and use the mild steel bottom plate as a quide to drill the lid. I keep some mineral spirits (paint thinner) in this jar and leave it on the gun when not painting - great for cleaning small parts. Replace the usual cardboard cap liner with one that will stand up to solvents. I made mine from some 1/16" thick teflon sheet. If you don't have any of this, cut one out of the flat, smooth side of a polyethylene bottle such as the ones motor oil comes in. The liner needs to be drilled with the guide. Use two 10-32 screws to fasten the lid and liner to the base of the gun so a jar can be screwed on as a paint container.

Now thread the brass vertical tube into the base, put on the lock nut loosely. Slip on the spring, washer and paint nozzle. Adjust the vertical tube so you can just get the paint nozzle on and off without hitting the air nozzle and tighten the lock nut in this position. You need to push a piece of plastic tube on to the bottom of the vertical tube. This tube should reach close to the bottom of the jar. I used teflon but polyethelyne would do. I'd be concered whether vinyl would stand up. You can always try it. I prefer a transparent material so I can see if it is properly cleaned.

The Al stand shown in the photos is too light to keep from being pulled over by an air hose. I plan to fasten a chunk of steel to the bottom to improve the stability.

Setting Up

Air flow through an orifice increases with pressure up to a certain point and then changes very little with further increase in pressure. The critical value for this gun is about 30 psi. Since it seems to have little, if any, effect on performance and the gun is plenty strong, I usually run off my (well filtered and moisture trapped) 80 psi line.

Fill the jar about 2/3 full of mineral spirits, put it on the gun, hook up the air and turn the paint nozzle down as far as it goes. DON'T force it, damn it! Now trigger the air and screw the nozzle up until the spray just starts. Back off one flat on the paint nozzle and mark the position. I made a light punch mark on one of the flats with an automatic center punch.

Preparation

Fill another jar about 2/3 full with paint. Attach this one to the gun. Have some appropriate solvent and shop rags, kleenex or toilet paper handy for clean up. Half fill a small container (I use an empty small tomato paste can) with solvent.

Using the Gun

Turn the nozzle up 1 to 3 flats, you will have to experiment, and paint. The more you raise the nozzle, up to a certain point, the more paint flow you will get. The paint droplets will also get somewhat coarser.

Cleaning up

When you finish painting, remove the paint jar and put on its lid (with an appropriate liner as discussed above). This is a convenient way to store small quantities of frequently used paints. Dip the end of the paint tube into the small can of solvent. If you turn on the air, the gun will suck up and spray out solvent. Now here comes the tricky part: With the air on, lightly tap a finger slowly up and down over the orifices of the two nozzles. As your finger comes down, it will deflect the air flow down into the paint nozzle forcing the solvent back down. As your finger comes up, the gun will suck up and spray out the solvent. This sloshing action and the solvent slopped around the nozzles when you do this has a very effective cleaning action. Repeat this process once or twice with some fresh solvent in the little can. Give a quick wipe with a rag and some solvent, re-install the solvent jar and give a short spurt as a final rinse and you're done.

Paint storage

Remember I said to use a jar that you could accumulate a set of? They make good paint storage containers (if you replace the cardboard lid liners) and you can set up to paint in a few seconds. You can use the drilling template you made to make one or more additional adapters to go on the gun for different size jars. With these and appropriate plastic pick up tubes, you could have, say, small, medium and large paint containers. There should be no problem handling at least up to a quart (a liter for some of us).

An Update to the Above (12/04/2007)


Email: Ted Edwards

Return to Home Page

Rev: 12/04/2007