subygirl said:
Apparently my post never went through the other day. I did a bit more research, and the highline meters do have an accuracy of +/- 3% which is 0.1mils. To clear up my previous point: If a meter has a resolution/accuracy of 5% or more, then they can have up to a 0.5 mil or about 12 micron discrepancy between the true paint thickness and what it is actually reading. This means that you can go through nearly 0.4 mils of clear and it still show the same reading - which is not very helpful imho. Many of the cheaper meters out there fall into this category, which is why I asked the question about the Highline meter's accuracy.
Negative. There are a couple of problem with your thoughts, so let me help in what ways I can.
To begin, in ALL cases, you're attempting to get an generalized thought of the paint you'll be working on. To think you'll be able to a measurement of the exact same section of paint is fictional. Even if you use the "laser method," you're not taking into account the reading width of the tool itself. Does a PTG measure a millimeter^2 ? A quarter of a millimeter^2? If you rotate the PTG in place (say 1/4 turn clockwise), how much does this affect the accuracy of your readings?
For a PTG to be +/- 3% is very accurate for our uses as the human margin of error AKA Operator margin of error is off by AT LEAST this much. This is why a PTG is used as a tool to learn more about the paint you'll be working on - to give an idea as to what we may expect from the thickness of various panels, to check for consistency of the paint, etc.
Ultrasonic Coating Thickness Gauges do exist, and can read on a larger variety of surfaces as you know. Carbon fiber, fiberglass, plastic, etc can all be measured... but not accurately. If you talk to Elcometer or any other company of the sort, you'll notice these devices are considered "Coating" thickness gauges as they are not meant nor designed for automotive use. Their margin of error is MUCH MUCH higher than the +/- 3% (the same amount that you seemed turned off by) when used for cars. They're primarily meant for things like wood - not the urethane coatings covering the rounded panels of automobiles. Of course this isn't going to stop vendors from selling these products to those willing to purchase them.
From what I've learned, the rounded nature of body panels are one of the biggest factors for the lack of accuracy by ultrasonic coating thickness measurement tools, but the other is the type of material they're be reading on as well. A standard car panel from the factory will AT LEAST have an E-coat, Primer surfacer and or primer sealant, THEN the base coat followed by the clear-coat. While clear-coats tend to be thicker in nature and applied much thicker as well, the difference between things like the base-coat and primer-sealer is very small. Small enough that even the Defelsko 200 Advanced (Ultrasonic thickness gauge that can read individual coatings) won't be able to differentiate between all the different coatings.
Other ultrasonic-based gauges exist, to include the Defelsko 200 Standard and several models from Elcometer (the UK-based company that owns Highline), but all of those are "total thickness" readers, just as the Highline PTG is on metal.
There continues to be a big debate on how useful a total thickness reading gauge is by detailers, and while individual layer readers are EXTREMELY useful in theory, in practice it's not quite the same.
Lastly, 3% is extremely good. Military-only GPS units are rated +/- 3-5 meters accurate while most civilian units are around +/- 10 meters. If you've ever used a +/- 10m accuracy GPS unit, you likely know how amazingly accurate they are despite them being 100%+ less accurate than the military versions.
Oh, and I'd highly recommend contacting Elcometer and/or Defelsko directly and ask their representatives yourselves if you have questions or question the information I've posted here. I've talked to representatives from both companies on multiple occasions and have found it to be a great help myself.
-Marc
). A few spots overthinned a little since the '70s doesn't seem so incompetent that I really oughta give up compounding instead of taking some readings now and then.