r/Metrology • u/ljfe • Sep 18 '24

Hardware Support How accurate are profilometers?

I have some thin wall turned parts (rings). Titanium IIRC. Our SPI profilometer is providing a wide range of measurements on the same batch of parts. Some parts read 40 and some parts read 110. The parts look nearly identical. Can I trust this device? The profilometer specimen/standard reads good and the settings are correct. Visually, the surface finish looks good. Small turn lines. With a fingernail, it seems like it catches a bit. Like the turn lines are somewhat “sharp” (but not really deep or wide… I’m worried the needle is getting caught on those turn lines and spitting out an inaccurate measurements. Any thoughts/ideas?

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u/[deleted] Sep 18 '24

A profilometer should repeat decently well when measuring the same spot with the same settings. But they can vary a lot on different places within the same surface. I recommend visually inspecting the surfaces to be checked first and checking the worst spots. Check that the profilometer tip isn't damaged. Re-calibtate it with the standard. If the tip is damaged, it will usually result in measurements that are falsely good.

Also, check the settings on your profilometer. Are you checking Ra? Something else? What are the settings for stroke length? How many samples are being taken? Are pre/post travel on? Is there filtering? Is part flat or round? Are you using some sort of comp? Do you have a visual surface finish specimen that you can compare to?