Spiral phase plate looking for advise on making shape..tia sal

Greetings all
I'm trying to make a spiral phase plate out of plastic (see link below). I have all the tools I'm just a little lost as
how I should procede. It doesn't have to be perfect or large. The Diameter would be just 5 inches

TIA
http://www.st-andrews.ac.uk/~www_pa/...ents/spir.html

From the URL this appears to be a section through a screw with a
square thread. What are your tolerance requirements and what
material will you be using? What is the change in axial
dimension through 360 degrees, i.e. the pitch or lead? Do you
require optical accuracy?

Depending on these factors, I can see a cnc lathe with live
tooling [i.e. Potts spindle] using an end-working tool set to the
correct helix angle generating this surface. I am cross posting
to the alt.machines.cnc newsgroup. Participants there are some
of the most knowledgeable people in the field.

What are you going to use this for? [death-rays not allowed on
these newsgroups]
=====================
On Thu, 16 Jun 2005 22:55:05 GMT, wrote:
Spiral phase plate looking for advise on making shape..tia sal
Greetings all
I'm trying to make a spiral phase plate out of plastic (see link below). I have all the tools I'm just a little lost as
how I should procede. It doesn't have to be perfect or large. The Diameter would be just 5 inches
TIA
http://www.st-andrews.ac.uk/~www_pa/...ents/spir.html

F. George McDuffee wrote:

From the URL this appears to be a section through a screw with a
square thread. What are your tolerance requirements and what
material will you be using? What is the change in axial
dimension through 360 degrees, i.e. the pitch or lead? Do you
require optical accuracy?

Depending on these factors, I can see a cnc lathe with live
tooling [i.e. Potts spindle] using an end-working tool set to the
correct helix angle generating this surface. I am cross posting
to the alt.machines.cnc newsgroup. Participants there are some
of the most knowledgeable people in the field.

What are you going to use this for? [death-rays not allowed on
these newsgroups]
=====================
On Thu, 16 Jun 2005 22:55:05 GMT, wrote:

Spiral phase plate looking for advise on making shape..tia sal
Greetings all
I'm trying to make a spiral phase plate out of plastic (see link below). I have all the tools I'm just a little lost as
how I should procede. It doesn't have to be perfect or large. The Diameter would be just 5 inches
TIA
http://www.st-andrews.ac.uk/~www_pa/...ents/spir.html



Assumption: That you are looking to use this in the same frequency bands
as were discussed in the indicated articles.

Free air wavelength at 38GHz is about 8 mm. The step on the phaseplate
will be an integral multiple of this. Surface finishes and form accuracy
are pretty loose even if 1/100 of a wave is desired (80u). This would be
a fairly simple job on a cnc mill.

--
jeff