Protrusion measurement gauge

[gs2deol]

Hi,

I'm having some trouble selecting a gauge to measure the protrusion of a curved plastic component in reference to a flat metal datum.

The protrusion spec was set as 0.3mm with reference to the edge of the protruded lens (lens has a cylindrical wall before transitioning into a curved surface)
I've since jumped into the project and am having trouble finding a reliable tool to measure the feature. So far I've tried feeler gauges and dial indicators but the inter-operator reproducibility and repeat-ability is very low. I'm going to try an OMM system next but I don't know if there's a suitable gauge for a feature this size.

Any suggestions would be appreciated!

 

[chez311]

gs2deol,

Is this in relation to a drawing/specification in accordance with an industry standard say ASME Y14.5 or ISO GPS? Or is it just a specification of "0.3 MAX" or similar?

Non-contact/vision measurement is certainly an option if you either have one available or can swallow the associated cost.

I'm not sure what the dial indicator setup looked like that you tried but you could use a similar setup to how flatness is measured with 3X standoffs (optimally round tipped standoffs, but 1-2-3 blocks are sometimes substituted) that contact the flat feature but instead of a single indicator use a pair of indicators, one of which has a round tip touching the flat surface and one having a flat tip which contacts the lip/protrusion of the lens (flat so you're guaranteed to touch the highest point). The difference between the two indicators would be your protrusion height. With some effort a custom gauge could be made with multiple indicators around the circumference to minimize the time needed to verify the protrusion around the entire diameter - or even simply using multiple pairs of indicators instead of the one pair I described.

An example below of how the setup looks with a single indicator for flatness. One could even possibly forgo the 3X standoffs since you're only concerned about the difference between the indicators, though it might help to have the consistent reference these create.

 

[3DDave]

Where on the lens is this measurement critical? Are the expecting to find the exact tangent between the cylinder and the eased radius or the theoretical intersection between the cylinder and the extension of the lens surface where there's no material present?

Optical comparator is the best bet.