Hidden Finishing Problems 10/5/2012 2:43:55 PM 
The other day I went into a shop to help a customer with a finishing problem. What I found was more than just a problem in his finish; many times what we think is the problem on the surface is just the tip of the iceberg of much deeper issues.
Turns out the cabinetmaker was having an issue with consistency, orange peel, moisture, pin holes and uneven application of film build. When looking closer at the equipment he was using I discovered the compressor he was trying to use was far too small and inadequate for the tools he was trying to run. His compressor was less than 2 hp, had a 30 gal. tank and produced just 3.5 CFM. He was trying to use a HVLP gun, and every time he pulled the trigger on went the compressor.
Not producing enough volume of air required to operate his spray gun effectively was the root of his problem. The lack of volume it produced was causing the compressor to run nonstop trying to fill the demand only to cause it to overheat. His air hose was coming right off the tank directly to his spray gun; you would have thought he was using a squirt gun instead of a spray gun hooked up to the air line. What was coming out of the air line was more water than anything else due to the hot air cooling and condensing once it reached his spray gun.
This is a common problem I see in many of the small to mid-size shops. Either they outgrow their compressors or they are undersize to begin with. It is important to remember the compressor is the heart of your shop — many of our tools run off compressed air. The airlines piped from the compressor are the veins to the areas in your shop, just like the veins in the human body they need to return or loop to keep it/us functioning properly. Dead ends are not efficient.
Picture your compressor with two lines running in opposite directions, now picture running a sander at one end and a spray gun at the other end. Who is getting the air first? Who is getting the most? If you loop the lines now the air is equal and balanced. The way your air lines are laid out, how the drops are piped and the type of material you use for your piping is also important. Remember to filter the air either by refrigerated driers or at the very least water separators or coalescent filters that will eliminate or help catch the moisture in your lines.
One important thing to remember is to have those filters at a minimum of 25 ft. from the compressor. Hooking them right at the compressor is a waste of your money, the air passing through at that point is nothing but hot air, the filter needs to be placed further down the line so the air condenses and the moisture can be trapped once it has cooled down. Coalescent filters or separators are like skimming fat off the soup, you didn’t get all the fat out but you did get the majority. Driers are a much better solution and they can be placed at the compressor.
When shopping for a compressor, first add up the CFM of all the tools you will ever run at one time then multiply by 1.5. This will give you the minimum size compressor you need. Don’t forget to take into consideration filters, length and diameter of hoses and piping you are going to use. You need to be sure that the air runs without kinks, obstacles, reducers, standard quick disconnects (when using quick disconnects be sure they are High Flow) and anything else that will cause it to alter its delivery to the tool. Think of the CFM requirement like how much money you need to make to pay your bills. Now think of the storage tank on the compressor as a savings account and the tools you wish to run as being bills you need to pay. See why you want to make more CMF than you draw from?
My customer didn’t have a chance getting a nice finish, his spray gun was sucking more air than the compressor could make and his hose was 50 ft. long ¼ in. ID so it was like he was trying to suck a shake through a coffee straw, it wasn’t happening. Every time he pulled the trigger, he instantly drew air from his tank because his spray gun needed 11 CFM and his compressor made only 3.5 CFM. Without the CFM being correct, he couldn’t get the fan patterns consistent, atomization, the material was building on the air cap, water was mixing with his air and finish.
No matter what he did, things just became worse. He thought maybe if he reduced the lacquer it would spray better. All this did was create yet another problem — pin holes and solvent pop. Sizing up his tool to the application would have solved all his problems and saved him the hours of rework.
Understanding the tools you use is paramount. Without knowing what you need, you can be sure you will always have a hidden problem lurking around the corner.
