Workholding Techniques

[Andrew Preisler]

I have a large glass meniscus that I am trying to pregenerate a spherical radius into for conventional polishing using a vertical mill. This sucker is big, almost 13" OD. My fixture plan is to use the posts shown with some UV cure. In the image, I have the lens with the concave side up and alignment is not 100% critical as I pregenerate the curve; however, when the lens is flipped, how can I ensure that the optical axis is still oriented perpendicular to the spindle axis?

Quantities for this part are on the order of several hundred a year. So some kind of simple drop and place fixture for the operators would be perfect.

 

[Houdini]

I wonder if you could mark the outer disk, probe or measure center from the marks.
then after rotation, probe or measure from the same points on the opposite side.
just thinking out loud real quick,

 

[brucecu]

When the blank is pre-generated can you machine a small flat at the convex perimeter? When flipped it should be as accurate as your initial set up.. You can reference it in a chuck or sweep it with an indicator for side two. Unless I'm missing something....

 

[eKretz]

Make a fixture like the lens makers do, with an external profile that fits the concave surface. You can use vacuum to hold it. Alternatively you could use a chuck with pie shaped nylon soft jaw inserts shaped similarly.

 

[stephen thomas]

If the OD's are consistent, it should be possible to simply make a split ring form that works for either side.
Similar to eKretz shaped pie jaws/chuck. However, a fixed ring bed with clamp ring might locate/repeat better with production help & may have less cleanliness issues.

 

[Andrew Preisler]

I wonder if you could mark the outer disk, probe or measure center from the marks.
then after rotation, probe or measure from the same points on the opposite side.
just thinking out loud real quick,

I think I'll use the top edge of a grinding pin to make a flat on the bottom surface of the stock so that way I'll have a full flat circumference to probe for OP 2.