I know PTG's for detailing are fairly common place in the US and UK, but here in SA there is no-one to my knowledge using one up until now. I've decided to post this here in any case as someone may find it useful :thumb: "Paint Detective (a UK based company) has 2 gauges, namely the original and widely popular PD8, and the newer, recently launched PD7. Essentially the gauges are very similar, both featuring almost identical resolution's, accuracy, etc. The newer PD7 has a calibration feature which is nice to have, along with a 10 measurement memory which will come in handy when measuring panels! Righty then, onto the actual PD7 gauge... The gauge comes in a hard, spectacle type carry case and includes 2 calibration blocks (Fe and NFe), a set of calibration shims and a set of instructions. The gauge itself is of very good quality and feels solid. The gauges come pre-calibrated but it is advisable to re-calibrate them prior to every use. The gauge up close... The μm/mil (+) button switches the unit of measure between μm and mils (more on this later). The Mem button allows you to scroll through the 10 stored readings. Finally the (-) button allows you to flip the display when taking readings upside down (can't think of anywhere on a motor car where this might be used, but it's there nonetheless). The calibration shims and blocks The calibration process is fairly straightforward and easy to complete. Having calibrated the gauge I found the readings to be well within the specified tolerances, generally coming up perfectly to the certified shim thicknesses. 102μm as per the shim 120μm = 4.0mils For those of you wondering what exactly μm and mils are referring to, here is a brief explanation... μm is the symbol for micrometer, more commonly known as microns. 1 micron is equal to 1 thousandth of a mm. Mils is the imperial equivalent of the micron, more commonly referred to as thou. As the name suggests, 1 mil is equal to 1 thousandth on an inch. If you are wanting to convert between the 2 then it is pretty straight forward. We all know that 1" (inch) is equal to 25.4mm, therefore: 1" = 25.4mm = 25400μm In order to convert the measurements all you need to remember is the following: μm = Mils * 25.4 Mils = μm / 25.4 So, from the photo above we can see that 102μm / 25.4 = 4.0mils Having calibrated the gauge I decided to take some readings from around the SO's car. Unfortunately it is pretty dark outside so no photies... :sorry: Prior to measuring the paint, I wanted to see if I could find a spot with little clear coat to get a good baseline reading from. Inside the door shuts the paint is fairly glossy which indicates at least some clear coat, nonetheless I took some measurements which all came in at around 60 to 80μm. Taking a look under the bonnet and in the boot I found 2 sections of flat paint, both of which consistently gave readings of between 30 and 50μm. With this in mind I took some readings over the entire car and noted the following: The frontal and horizontal areas (roof & bonnet) all have significantly more clear coat than most of the vertical panels. Readings on the bonnet and front fenders range from 130 to 150μm, with the roof measuring an average of around the 130μm mark. The doors and boot area all measured between 110 and 130μm, indicating slightly thinner paint. Having seen the flat, clear-coatless areas reading in the 30-50μm range, the inner door shuts around the 80μm mark, and almost the entire exterior reading above 120μm, one is led to believe we have roughly 70-80μm worth of clear coat on the vehicle. 'Fortunately' I had the perfect test section to get some clearer readings from. An old, rather large stone chip that I had successfully filled, and subsequently in my over zealousness polished through, allowed me to clearly see the layers that made up the paintwork. Perfect for taking some readings from... The inner-most area has only primer and some basecoat remaining, measuring up at 35μm. The surrounding area that is still slightly dull reads around 45μm, with the remaining shiny areas building up from around 55μm to well over 120μm. Generally it is said that removing more than 20-30% of the clear coat could lead to complete failure of the coating. If we assume an average thickness of 70μm for the clear coat, this would mean that removing more than 15-20μm could potentially compromise the paintwork. With this in mind I will try to polish some small sections with various polishes (compounds, polishes and finishing polishes) to see what sort of removal rates the various products deliver (shamelessly stolen from DaveKG's research ideas :applause2 :thumb:
