Elliptical Helix

Anonymous — Fri, 10 Jun 2005 02:46:56 GMT

Elliptical Helix

Hello,
Has anyone successfully made a library part that
draws an elliptical helix with an angle type parameter
allowing any sweep angle or included angle of arc
to be set by the user ?
I have looked in Objects on Line and other places
and have not found anything close.
I expected to find such an object because of it's obvious usefulness
for making things like handrails for elliptical stairways or ramps etc.
Apparently, this is not easy because I have not found such an object
and I was hoping I would so I could see how it was done.

I thought of making this object using BPRISM but rejected the idea
because the only way to get an elliptical shape with BPRISM is to
use the MULL command on the whole object which distorts the width
of the helix cross section from a maximum on the major axis
to a minimum on the minor axis. Using a MULL command is no good
for making a elliptical ramps or handrails.

I tried to make such an object using the TUBE command but
TUBE tilts the corners of the facets of the arc to the angle
defined by the incremental elevation change along the path.
This plays havoc with the object when an elliptical shape
is generated and even when the shape is a circular arc
there is distortion caused by this tilting.
This distortion is not apparent when one is setting the parameters
to draw a shape having the proportions of a ramp but is very apparent
when setting the parameters to draw a shape
having the proportions of a handrail.

I tried making this shape using the SLAB_ command
to get around the tilting problem but when the angle is not
a multiple of 90º the outside end corner of the helix
is a point I don't know how to define in Cartesian coordinates.

I hope someone has made an elliptical helix with variable sweep angle
and would be willing to give me some clues about how it is done.
Thank you,
Peter Devlin

Re: Elliptical Helix

Frank Beister — Fri, 10 Jun 2005 06:52:04 GMT

Once I have modified (and unfortunatly translated to german) an object of DNC (hspiral.gsm) from the cookbook. With this you can make an eliptical spiral. If its OK for David, I can post it.

topic Re: Elliptical Helix in Libraries & objects

Elliptical Helix

Re: Elliptical Helix