spiral sweep

Hi group,

does anyone know, how to model a spiral groove on a cone? Well, that
alone is easy enough, but I want that groove to end in the middle and
leave a shape as you would see, if you have a endmill make that groove
with ramping out at the end of it. If I use a rectangle (2D projection
of the tool), the end is wrong (as is the exact shape of the groove
itself). All I can think of is to create multiple points on the
trajectory for the groove and cut out holes perpendicular to the cone
down to those points. Then I wold create surfaces to connect the sides
and the (somewhat) round bottom of those holes to complete the cut. This
approach seems to be quite complex and only would give me an approximation.


Any better ideas on how to create a true 3D-cut?

Tom

 

Sweep your rectangular cross section. Then round the ends as follows: create
a revolved cut using the flat end of the previous cut as a sketching plane.
Place a center line in the middle of the plane for an axis of revolution.
Then made a rectangular sketch aligned to the centerline and the top, bottom
and side edges of the existing cut. Make the degrees of revolve 180 and it
will round the ends. Make sure that the height of the cut is above the top
of the cut. Also, the sketching planes will be no problem, but you may have
difficulty, especially on elliptical geometry of a cone, of finding
something to use as a vertical or horizontal reference. You may have to
create datums, possibly on the fly, for this purpose. You can use the
sketching plane as a normal reference and thru the bottom edge of the
existing cut.

I predict complete success in your nutty endeavor.

David Janes

 

Hi David,

thanks, and I will be a complete success ... but not to what I need. A
rectangluar sweep won't give me the correct geometry, since in a spiral
cut parts of the cutter before or after the recangular crossection of
the cutter will remove material as well - this is not modeled with your
approach. Also, I do not want the cut to end at the same depth as the
groove, but to move out of the material while still feeding. So the edge
on top of the material will not be a circle but some kind of ellipse.
Here, mostly the front part of the mill (before the x-section through
the centerline) will do the material removal.

But thanks anyway, I probably have to model the mill on several places
to remove material and then conect those cuts with a surface to finish
my groove.

Tom

 

Tom,

Maybe a "Variable Section Sweep" would be in order here? With this
feature, you can specify that the section always remains normal to the
trajectory and you could achieve the blend-in and blend-out by moving
the sections onto or off of the trajectory curve. With the section
specified as normal to the curve I think that you would get the correct
"as machined" geometry that you are looking for.

Ron