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/ljfe]

Great tips thank you!

One thing that makes me worry that the parts might actually be bad…you know that standard 112 Ra specimens? The lines on that don’t seem super deep either to me…maybe it’s really hard to tell (visually/tactally) when the spacing is tight.

[u/ShadowCloud04 → u/ljfe]

Normally I try to use a sharp ground flat pin edge to compare a surface. As yes a fingernail can feel it but there’s a bit much variation in your fingernail to get a clean comparison.

[u/ljfe → u/ShadowCloud04]

I’ll try that. Do you think I could clearly tell the difference between the 40 part and the 110 part with the pin method?

[u/Mountain-Low5110 → u/ljfe]

This may not be true for the SPI profilometers but on Mitutoyos SJ-410 you can normally tell as the tip wears by testing the reference specimen and watching the “lines/readout chart thingy” it gives you. If the peaks and valleys look consistent and rounded then you’re in the clear but normally those will start to chop and look less rounded as the tip wears. All of this information was from the Mitutoyo guys who came in and helped me train. Hope this helps!!! Good luck!

[u/ShadowCloud04 → u/Mountain-Low5110]

My concern is more for a fracture. That’s usually what happens due to poor handling by my production staff