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Locating the center of a cylindrical optic

Locating the center of a cylindrical optic

Locating the center of a cylindrical optic

Hi all,

I have attached an image for my question.

I have a cylindrical optical housing (red). It sits on a machined part which essentially mimics a V block (black). The red circle in the picture is not at all a feature on the machined part.

I'm interested in controlling the location of the central axis of the optic...at the end of the day, all of the optics in the chain need to be aligned to some extent.

What I've seen some people do in the past is on the machined part drawing (the V block) they would draw, in phantom, the outline of the optic (red) and hit it with a positional tolerance. I'm not sure I'm seeing anything in Y14.5 that really permits something like this. I think, in theory, the hope was that the inspector would place a cylindrical pin in the V block that mimics the shape/form of the optical housing and then inspect the postional tolerance of the cylindrical pin in the V block. Is this allowed? I guess my initial thought was no but I'm curious to hear your thoughts.

I guess I was thinking that the central axis is really a child of the V block and not one I can control directly and, therefore, I have to apply my GTOLs to the V block (for example, a profile) such that the central axis winds up where I want it.


RE: Locating the center of a cylindrical optic


Your inspector has no access to your optic. Your phantom circle would be just like a centre line. You cannot apply a tolerance to it. It is figment of your imagination.

You could design an inspection tool to mimic your optics, and write out a procedure to use it.

Failing that, you need to control your V block faces.


RE: Locating the center of a cylindrical optic

Specification over an inspection pin represented by a phantom line circle isn't allowed OR forbidden by Y14.5, it simply isn't covered/supported.  You would need some clarification on the drawing of what the positional tolerance applies to, but I suppose most inspection people wouldn't have much trouble figuring it out anyway. As opposed, in the ISO standards they have a concept named "contacting feature" exactly for that. Considering Y14.5 though, if you want an unambiguous specification of the limits of the V angle value, you should specify profile of a surface and not a directly toleranced angle. If you do that, you may as well call out the appropriate datum references to locate and orient the V. The profile tolerance could be composite to refine the form and angle. This may address functionality less directly than controlling the position of a pin mimicking the optical housing, but it is more direct in the sense of controlling the variation of the part surfaces themselves to achieve whatever you want.

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