Making external threads in SolidWorks
It is not exceptionally hard to make an external thread in SolidWorks that
actually looks like a thread. This is not necessary since it is possible to
make external cosmetic threads just like the internal cosmetic thread made
by the hole wizard.
To make an external cosmetic thread:
- On the top menu bar select Insert -> Annotations -> Cosmetic thread.
- Click on the circle that is the edge of the rod at the end that
you want to thread.
- Select "ANSI Inch" standards, 3/8-24 NF threads, "blind threads,"
and the proper length.
- Click on the check mark to finish the thread.
There is even an option to make the cosmetic threads look something
like a real thread. Select Tools -> Options -> Document Properties ->
Detailing and click on the box for "Shaded Cosmetic Threads." This
will slow drawing down a little but the computers are fast enough that
it isn't too noticeable.
Here is the process to make a realistic-looking thread:
- Draw a circle on the end of the rod with the same radius as the rod.
- On the top menu bar select Insert -> Curve -> Helix. Set the
parameters of the helix correctly for the desired thread pitch and thread
length ("Pitch and Length"). The length of the thread is specified on the
example drawings. The pitch is determined from the specification of the
thread. "3/8-24 NF" means that the thread should be nominally 3/8"
diameter, with a pitch of 24 threads/inch. The "NF" means that it is a
standard thread known as "National Fine." The pitch is in inches/thread or
1/24". You also need to select a starting angle that will result in the
starting point lying in one of the predefined planes. From experience I
have found that you generally want the helix to start in the "right" plane
to simplify some later steps. This can be selected by either 90o
or 270o. Again, from experience, the best choice is
270o which will place the end of the helix in the right plane
on the "lower" side of the rod - this means that if you select the "right
view" from the top menu bar and the helix is on the left end of the rod then
the starting point is in the lower-left corner of the horizontal rod. If
the helix is on the right end of the rod then the starting point is in the
upper-right corner of the horizontal rod. If the helix extends into space
you need to reverse the direction in the definition panel.
- Change to the right view (so the "right" plane is the plane of the
screen) and zoom in on the helix.
- Click on the "Right" in the list of objects on the left side of the
screen to select the right plane for drawing.
- Draw a 3-sided polygon (triangle). An equilateral triangle is
probably appropriate, or at least adequate. The length of the base of the
triangle needs to be just slightly less than the pitch distance on your
helix. Draw this separate from the rod to be threaded so you don't get
any unexpected constraints placed on the triangle. You should have the
triangle oriented so that if you place the base on the starting point of
the helix the apex of the triangle will be toward the center of the rod -
it represents the cut that will be taken out of the rod. The size of the
triangle is usually specified by either a circumscribed or an inscribed
circle. For your reference, the radius of an inscribed circle is given
by r=l/[2*sqrt(3)] where l is the length of the base.
- Align the triangle with the helix. The best choice is to have the
triangle extend out from the end of the rod so that it cuts clear to the
end. The ideal choice is to position the rod so that the apex of the
triangle (the end toward the center of the rod) is actually on the end of
- On the top menu bar select Insert -> Cut -> Sweep.
- Select the triangle as the profile and the helix as the path. If
preview is turned on it will immediately indicate (usually in yellow) what
is going to be cut if you have done this properly. If it can't complete
the cut it is usually because your triangle is too large so that the cuts
overlap. It is also possible that is will make the cut but you can't see
the threads because they are cut entirely inside the rod. This will happen
if the base of your profile triangle is too close to the surface of the rod.