[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: [ATM] Lens Wedge
Alfredo,
I am not sure what the list etiquette is regarding pictures - I can
possibly send some to you and others who are interested off-list.
In words, I have a precision 'turntable' (picked up surplus), which can
either be rotated by a variable speed motor or by hand. The top of the
turnable is a thick brass circular plate. On top of the plate, I marked
three radial lines (120 degrees apart), and fixed three 1/4 -inch
precision glass balls (with J-B Weld, fixed to the top of a nut, so they
wouldn't roll when the epoxy was setting, and to give the glass ball
more physical support). Before the J-B Weld set, it was very important
to make sure the balls were all equidistant from the axis of rotation
(with a dial indicator, as the turntable was rotated). Then I J-B
welded a small piece of cork on top of each glass ball to protect the
heavy blank. The trade-off here is that cork is slightly compressible
(possibly giving rise to errors in measuring wedge), but I needed that
'comfort zone' to protect the valuable blank. When the cork was set, I
placed another very accurate (both sides parallel) brass plate on the
three supports, and measured any wobble as it rotated (with a dial
indicator). The entire turntable was then carefully shimmed to be
horizontal when rotated (using a dial indicator and a set of various
thickness brass shims). The result was three padded supports, at the
same radial distance from the axis of rotation, and the same height as
the turntable was rotated.
Before I put the blank on the supports, I added a sheet of "Saran Wrap"
over the supports, so the blank could slide a bit easier for exact
positioning. When I put the blank on the supports and rotated the
turntable, I ensured that it was precisely centered by measuring its
edge and getting no appreciable movement on the 'horizontal' dial
indicator. I then have a 'vertical' dial indicator set up to measure
wedge as it's rotated. But I also have 6 marks (60 degrees apart) on
the blank's edge. Once I take one set of readings, I lift the blank
from the turntable and reposition it +60 degrees with respect to the
turntable. Then take another set of readings. In all, I take 6 sets of
readings (to minimize errors caused by unresolved turntable wobble or a
slight error in support heights). If all readings indicate some 'wedge'
in the same place on the blank, I'm pretty confident that it's real and
not measurement error.
Hope that helps!
Like I said, it may be overkill.
James
aneves wrote:
> Hi James,
>
> Could you share more details on your wedge tester (sounds interresting)? Maybe some pictures!
>
> Regards,
>
> Alfredo
>
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>
>
>
_______________________________________________
ATM mailing list http://www.atmlist.net/