How to measure 0.5mm bump on a flat surface?

[samuelr]

If I had a flat disc how can I measure that is really flat? I was thinking of a laser based distance sensor and running it down the disc not sure if it can achieve 0.5mm accurate read.

 

[123jack]

Have you had your balls checked lately ;-)

I'm not sure of how much your want to spend and so on but a waveometer can be used to measure roughness.
Whether you could build a low cost one I dont know but it might be worth the effort.
But perhaps for 0.5mm a mechanical engineers straight edge could do the trick?
Again it depends on exactly what you need to do and where and how often etc.

This site is about bearings but you get the idea: https://www.precisionballs.com/TDS/tds14.htm

 

[samuelr]

Interesting, they seem to be using interferometer. I want to measure a disc like a wafer. If there is std. product why not, but where is the fun in that

 

[123jack]

If there is std. product why not, but where is the fun in that

Indeed.
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