Chapter Ten - Painting


The gun is one of the most important pieces of equipment in painting. Most people who wish to start painting bicycle frames find it hard to choose the correct painting gun and cup. Here are a few criteria to go by in making that decision.

1. Make sure the gun is large enough to handle the job. An airbrush, Figure 10-8, is a scaled down version of a paint gun. Some people may have a tendency to buy an airbrush because it is small and so are bike frames. An airbrush is for very fine detail work and should only be used as an extension of what can already be done with the existing paint gun. A skilled technician can do something as fine as pinstriping with an airbrush. If an airbrush were used to paint a whole frame, it would have to be refilled many times because the cup capacity is so small. An airbrush should not be purchased until skill and technique are developed with a regular gun and cup.

FIGURE 10-8: An air brush

FIGURE 10-9: A Binks 115 touch-up gun

FIGURE 10-10: A large Binks gun suitable for automotive work

2. Make sure the gun is small enough to handle the job. Many guns are quite large and heavy. A large gun such as the Binks, shown in Figure 10-10, is quite large and would be unwieldy in a small paint booth such as the one described earlier. It has a 1 quart cup, which is more than necessary for painting a frame. The only time any of these guns would be recommended would be for production work where many frames would be painted the same color and the excess left over at the bottom of the cup is not wasted as often. Another time a larger gun could be used would be for priming a run of bikes. Another disadvantage of a large gun is that the fan pattern may not be able to be adjusted down small enough to do a bike frame efficiently. The primary consideration with a large gun then turns out to be "waste."

3. The gun and cup (often purchased separately) that best fit these criteria are usually referred to as a "touch-up gun."This is just the right size. (Hey, does this sound like a familiar fairy tale?) Binks, DeVilbus, Badger, and Sharpe all make touch-up guns. They all fit easily into the palm of the hand, have the necessary stainless and teflon parts, and hold approximately 8 oz. of paint, which is about enough to paint one frame set. The gun shown in Figure 10-9 is a Binks 115 touch-up gun. (I switched to a Sharpe touch-up gun several years ago because the trigger would work for either a right or left handed person. This allowed ALL of my framebuilding students to easily paint parts of their frames. I continued to use a Binks cup because there was no lip around the top; this particular cup is much easier to clean because of that feature.)

There are currently a lot of paint guns available that are manufactured in third world countries. (Oh boy, don't get me started on the outsourcing of the American job market!) One is often tempted to purchase them because they are 1/3 the price of the brand name guns. These things are JUNK; don't buy them! Settle only for stainless steel needle valves and orifices with teflon seals. Gaskets should be made of leather or rubber. Some cheaper guns will use aluminum in place of some stainless parts, plastic in place of other metal parts, and paper or cardboard gaskets. A cheaper gun with aluminum castings and plastic parts will wear out quickly and deliver a poorly formed fan pattern after only a short period of time. (Aluminum is an acceptable material for the cup.)

The principles which make the paint gun operate are simple. Air rushes through a horizontal tube and passes over the top of a vertical tube which is submerged in the paint. This airflow causes a reduction of pressure at the top of the vertical tube. At this point, the only thing that can happen is for the paint to rise in the vertical tube. When the paint reaches the top of the vertical tube, it is caught in the airflow at the front of the horizontal tube. The airflow then forces the paint forward. There is a very simple device that art students once used, consisting only of these two pieces of tubing--a mouth-operated spray gun shown in Figure 10-11. Perfume spray bottles are another variation of the same principle; they have a supply of compressed air (the bulb) and a nozzle to spread out the mist. From this point, further embellishments can be added: air pressure control, fan size control, and fan rotation control. Add the correct size of cup, necessary stainless steel and teflon parts, and a compressed air supply and "Voila!," you have a gun suitable for painting a bicycle frame. Figure 10-12 shows another basic "paint gun" -- a perfume bottle.

FIGURE 10-11: Basic concept spray gun

FIGURE 10-12: A perfume bottle

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