Problem with a helical sweep (image provided)

Hello

I have been trying to model a funky part that basically looks like
cylinder that has had a helical sweep cut along its length. The pitch
of the actual helix that defines the cut path actually varies every
1/4 of a revolution getting progressively smaller. The cut profile of
the helical sweep cut is defined on a plane that is coincident with
one end of the helix and parallel to the axis of the cylinder. The
intent is to keep that orientation throughout the sweep.

Now the curious thing is that if I start the helical swept cut at one
end of the cylinder and terminate it at some distance BEFORE the end
of the cylinder, the face which is created at the termination is NOT
parallel to the cylinder axis (as the original cut profile sketch
was), but it is at some angle to it.

Look here: http://members.iinet.net.au/~lt.bull/Helical_sweep.JPG

How can I ensure that the profile that sweeps and cut along the
helical path stays paralel to the cylinder axis throughout the length
of the helix?
ie. the profile plane must always remain parallel to the cylinder
axis.

Cheers

Bullman

 

Hi

You get that effect because the top part of the cylinder is tapered.

steve

 

You get that effect because the top part of the cylinder is tapered.

Aparently not. Here is a screen shot , same helix but with cut
termintating on straight cylinder section, same angled plane.

http://members.iinet.net.au/~lt.bull/Helical_sweep2.JPG

 

Bullman,

Have you tried tuning on "align end faces" in the sweep options ???

Your part looks like a lead screw for the component strip reel cartridges on
a surface mount machine.


Mark

 

Yes I have tried that but still get the error. The error actually
says "The sweep can not be completed becasue it intersected itself
whiel passing through segment #1 of the path. This may have been
caused by: (a) the path pasing too closely to itself:Check to make
sure it does not pass too closely. (b) the way the section swists as
it moves along the path: Check that the Orientation/Twist Control
setting is correct. If the "Align to End Faces" box is checked, the
end faces may be twisting the section too much relative to the path.
Note: If the sweep path is not normal to the section, the entire path
is consiodered to be #1."

I have given up on using a profile that is defined on a sketch that is
parallel to the cyliner axis, though this is truly the design intent I
want to maintain throughout the sweep cut.

I have instead now tried to achieve an approximate result by defining
the cut profile on a plane that is NORMAL to the helix (as opposed to
parallel to the cylinder axis). I project the sketch that I created
on teh parallel plane onto this sketch that is on a plane normal to
the helix as a start. I still had to manually tweak the dimensions of
that profile sketch to get the right cut on the cylinder. But the
important thing is that I can now have my variable pitched helical cut
continue right along the length of the cylinder. It is important to
note however that again true design intent is not completely
maintained throughout the helical cut as the helix changes pitch (and
hence the normal plane angle) and that affects the way the profile
cuts the "valley".

Here are some comaprison shots-
Using parallel plane to cylinder axis for profile (note SW wouldn't
let me continue the cut any further than what is show):
http://members.iinet.net.au/~lt.bull/PARALLEL.JPG
Using the normal plane for profile:
http://members.iinet.net.au/~lt.bull/NORMAL.JPG
Superimposed:
http://members.iinet.net.au/~lt.bull/SUPERIMPOSED.JPG

Not sure of what you mean, but this screw sits horizontally along a
production line/conveyor along which bottles are stacked up on.
Bottles enter the screw at one end, and are pushed along as the screw
rotates, unifromly spacing the bottles in the process as they exit the
other end of the screw. Hence the design intent was to have the same
shaped "valley" (when viewed perpendicular to the cylinder axis) along
the entire length of the screw despite the change in pitch. My
approximate solution will do, however still interesting to know if SW
could somehow be used to cut a path along the entire length of the
helix exactly as per my design intent.

 

Just realised I didn't answer your question in the right context. The
answer is yes I have tried that but still the terminating profile is
at an angle. The answer I gave above however was in the context of
what i believe to be the related problem (one that I hadn't mentioned
but was ultimately trying to solve) which I believe comes about
becasue of this progressive angling of the profile plane despite it
starting off parallel to the cylinder axis:- and that is, for some
reason, if I define a helix that would extend along the full length of
the cylinder (ie. beyond the 2.6 revolutions shown in PARALEL.jpg),
SW will return the error I mentioned above an, effectively preventing
me from making a helical cut along the entire length of the cylinder.