Q: I am an avid fan of the “Orange County Choppers” television show. This is the program about a shop that customizes motorcycles. Very often, they use powder coatings as their coating of choice. They will send out parts to a job-coater to be finished with an exotic-looking powder coating.
It seems that they regularly run into problems with the part dimensions after it has been coated, though, causing them to send it back to be recoated. What’s the reason for this? Is there something inherent to powder coating that causes this?
A: I have only seen the show a couple times. If you cut through the contrived drama that this “reality” show stages, the actual work these guys do is quite impressive. It’s pretty amazing seeing them transform a mundane bike into a work of art.
Your observation regarding problems of the fit of powder-coated parts is insightful. Here is what I think is happening. The parts are stripped of any old paint, then cleaned and pretreated prior to the application of the selected powder coating. The parts are then electrostatically coated and cured in a convection oven.
The goal of the job-coater is to create the finest looking part – smooth as silk and completely free of defects. This objective is most easily achieved with a relatively thick coating of powder. Recall that, unlike liquid paints, powder coatings can be applied at thick films without concern for sags, runs, drips, or solvent popping defects. As a result, it is fairly common for a custom coater to apply more powder than is needed.
So what is the root of the problem? Part of it is culture, part of it is specification. When a motorcycle is manufactured by the original equipment manufacturer, their engineers hold both parts and materials suppliers to very exact specifications. This includes the coating’s physical and performance quality, as well as the amount applied and how it is cured.
Aftermarket rebuilders such as Orange County Choppers probably do not hold job-coaters to the same stringent specifications that OEMs do for their suppliers and finishing shops. Hence, the job-coater is unaware of the strict tolerances needed to reassemble a precision machine such as a customized chopper.
It’s really not the coater’s fault; rather, it’s incumbent upon the rebuilder to specify the coating thickness tolerances that will allow for trouble-free reassembly. The solution to this nagging conundrum is for the madcap mechanics and wacky artisans at the chopper shop to understand the tolerances required and then communicate and hold their job-coater to them.