Optical Axis alignment not for GD&T? 1

[SpaciouS]

Can you use GD&T to establish and/or inspect a light source relative to datums of the physical part?

At my company, we detail external interfaces of lens assy's (lens housing with optical lenses internally), and we have vendors that develop the internal Optical Axis (OA). An OA is established by moving optical lenses around relative to each other and testing each configuration with a light source until you achieve a desired light path. Our drawings identify position and perpendicularity FCF’s of the OA relative our external interfaces. These FCF’s are pointed the arbitrarily to the axis of the lens assy. The tolerance zones are also projected in space to a specified distance beyond the lens assy.

I’m not sure if this is a matter of using GD&T here… any comments?


Thanks,
Sean

 

[drawoh]

SpaciouS,

Your link does not seem to work.

What are you trying to do, prepare fabrication drawings, or document a lab setup?

GD&T will not create your optical setup. It only allows you to describe it to co-workers.

JHG

 

[MechNorth]

The problem that I see is that GD&T fcf applies to physical features, not construct/representational lines (i.e. the graphic representation of the OA). As such, the standard doesn't allow a fcf to be applied to a construct/centerline. To get around that, you could use phantom lines to represent the column of light exiting the lens (label it as such), then put the fcf on one of the phantom lines representing the boundary of the column.
I am curious how they determine the specific axis of the column, though. Is it that the entire column has to be within the projected tolerance zone, or just the very center?
Interesting application. I look forward to seeing your graphic and hearing some details if possible.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[drawoh]

MechNorth,

If you have a test that tells you where the optical beam is, to some level of certainty, you can use GD&T to specify that certainty on a fabrication or assembly drawing.

If the OP is trying to prepare drawings, and he is willing to select fixturable features as datums, I would think that GD&T will work.

JHG

 

[MechNorth]

JHG, I thought I said that?

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[SpaciouS]

drawoh & MechNorth,

I apologies but I can't seem to get the link of my image to work...

I agree with both of you:

MechNorth
Using phantom lines to represent a cylindrical tolerance zone exiting the lens and over a desired distance is what I suggested (we don’t care what the OA is doing internally). What I was thinking was, I would add dimension arrows to the phantom lines, replace the value with the label, OA (as you mentioned too), and below continue with a FCF (in this case a position/perpendicular double segment FCF). But I'm still trying to find the right expert to answer one important question about whether there is an inspection specification or acceptance criteria in particular that we use, and if so I would like to add below the FCF, ACCEPTANCE CRITERIA PER...

Drawoh
You mentioned the something about a test to verify where the optical beam is, and that is what I'm still trying to find out. I don't care, more or less, about what type of test is used to determine where the optical beam is, as long as it meets a recognize inspection criteria. I'm fairly new at this company and I’m finding it difficult to get that information.

Recap
•Phantom tolerance zone representation exiting the lens and over a desired distance
•Attach dimension arrows to the phantom lines with a label (no dimensional value)
•Add FCF (with diametrical symbol indicating a cylindrical tolerance zone)
•Add note: ACCEPTANCE CRITERIA PER...

What do you think?



Thanks,
Sean

 

[MechNorth]

I think so.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[drawoh]

SpaciouS,

The first step is to establish datums on your hardware that you can fixture to and measure from. Then, your steps work.

JHG