My son made me promise this was really a model of lip balm… less girly I guess, if you’re willing to overlook the flowers on the decal, that is. Sorry, I couldn’t resist! Not that I usually wear lipstick, err, lip balm, but when stressed out to the max and whenever tossing a 12 lb ball at a group of unsuspecting pins won’t make me feel any better,   I often find solace in regular things and activities that have long been considered exclusively feminine. That’s the good thing about being female! Yep, sometimes even a dab of lipstick can do the trick! Ah, but this one here is no ordinary lipstick! Putting this SolidWorks model together was possible thanks to the use of two special mates: the screw mate and the width mate.

OK, so this is the lipstick assembly. It is made out of three different parts: One I’ve called the lipstick bottom, which is the part at the bottom of the tube, the one that you usually twist in order to get the color to come out. This part is cylindrical and has a couple of vertical guides (slots) on each side.

Another part of this assembly is the one I called lipstick top. This cylindrical part has a couple of helical guides on the inside, and the cylindrical part previously described (lipstick bottom) fits inside of this one.  The helical guides were created using a sweep cut of a rectangular profile following a helical path. The helical path describes only one revolution as it travels from bottom to top of the part. Notice in this case, the cylinder has a height of 2 inches and that’s precisely the pitch of the helix. The second guide is created by patterning the first cut.

And finally, the third part is what I called the lipstick content. This is the part that has the creamy color. This is also a cylindrical part with a couple of pegs on the sides. These pegs will have to follow both the helical and vertical guides on the other two parts for the lipstick to work as such and for the color to travel up and down the tube as the bottom part is twisted. The idea is simple, as the bottom twists, the vertical guides push on the pegs and force the content part to rotate; as the content part rotates, the pegs follow the helical path on the lipstick top part (which remains immobile), thus translating the whole content part up or down, depending on the direction of twist.

How to make sure the pegs follow the guides? Well, this is where the mates come in handy! First, the width mate. The width mate is a very simple, yet extremely useful, mate among the advanced mates available in SolidWorks. What it does is to center the peg within the width of the vertical slot.  In order to use this kind of mate you will always need to provide references for the width (it could be a groove or some cavity and you’ll need to provide two parallel planar faces or two non-parallel planar faces) and for the tab (two parallel planar faces, two non-parallel planar faces like in a wedge, or a cylindrical face or axis). In my case, my tab reference is the cylindrical face of the peg and my width references are the two long planar faces of the vertical slot.

And now for the screw mate. This is one of the mechanical mates available in SolidWorks and what it does is to constrain the movement of two components to be just like in a real screw, concentric and with a pitch relationship between the rotation of one component and the translation of the other. What it means is that by applying this kind of mate to the lipstick content  part (the one with the pegs) and lipstick top part (the one with the helical guides), the rotation of one of these parts will cause the other part to translate along the axis.  As you can see in the image, I selected the axis of each part as the entities to mate and set a distance/revolution value of two inches, because, if you remember, that’s precisely the pitch of the helical path that was used in creating the guides. This means that, as the lipstick bottom part rotates the lipstick content part with travel 2 inches up or down per each revolution. This will make it look like the peg is actually following the helical guide.   The option to reverse the movement simply changes the direction of movement, clockwise or counter clockwise, as needed.  

After applying a few other mates to the assembly, such as mates to prevent movement of the lipstick top part (the one with the helical guides), we have a model of a lipstick that works pretty much like the real thing and we can see it move simply by dragging the components or by using SolidWorks Animation.