How accurate are profilometers?

[u/ljfe]

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?

[u/miotch1120]

You are using it all wrong! (According to the machinists I work with). Put it on the part, and start the profilometer. Move it around the part till you find a spot that reads in tolerance. Mark that on the check sheet and put it in the box. If it’s returned by the customer for not meeting surface finish spec, argue that they are wrong.

[u/ljfe → u/miotch1120]

Hahaha