I was recently asked to provide a couple of model heads for a product presentation. Since then, a number of people have wanted to know how I constructed them. For the beginner, this exercise can be a fun and interesting introduction to surfacing.

(You can click any image in this article to enlarge it.)

For each head I used four Variable Section Sweeps. I created surfaces in the two left-side quadrants of the head and mirrored them over to the right side. I’m sure there are other ways to do this, but this technique was the quickest for me.

Here’s how I did it, starting with the larger head.

Step 1. Create six datum curves.

Although you can create curves in the surface feature, I prefer to create them separately because they’re easier to modify and manipulate as independent entities.

Create CURVE_1 by aligning a straight line 13” long to a centerline created between the FRONT and RIGHT datum planes (Fig. 1). Note: You must align the start point of CURVE_1 and the bottom of the other curves to the top datum plane.

Figure 1. Basic curve for the ORIGIN TRAJectory of both left-side surfaces.

The next five curves represent the head profiles. Each curve has about 19 points approximately _ of an inch apart (located roughly as shown in Fig. 2). Start at the bottom and try to sketch the approximate shape using the sketch datum curve through points command (the lazy S icon). Complete accuracy isn’t necessary, but the closer the better. Use these dimensions in the beginning and then modify them when you have a completed feature.

Figure 2. Front profile of the head.

The centerlines are created perpendicular to the datum planes. The ends of the curves are then constrained tangentially to these lines to provide smooth transitions where the surfaces join.

Align the top centerline to the top of CURVE_1. Align the top end of the current curve to the top end of CURVE_1. When you’ve completed this curve, try modifying it in the sketcher. When the Modify Curve window opens, you can change the shape of the curve to your liking. The Show Curvature box and the Control Points options are especially helpful for smoothing out your curves. The box is mostly self-explanatory.

Draw CURVE_3 on a datum plane created on the fly through the center AXIS and at 30 degrees from the right datum plane (Fig. 3). Remember to align and constrain both ends of all curves.

Figure 3. Outline for the left-front corner of the head.

Figure 4 shows the left-side profile (CURVE_4) drawn on the front datum plane.

Figure 4. Left-side profile.

Figure 5 is the left-rear “corner” profile (CURVE_5) drawn on a plane. Create this one on the fly at an angle of 145 degrees from the RIGHT datum plane.

Figure 5. Three-quarter profile.

Figure 6 shows the final curve, which is created on the RIGHT datum plane and represents the back of the head profile. Your model with all the curves should now look like the one in Fig. 0.

Figure 6. Rear profile.

Step 2. Start creating surfaces.

Beginning with the left-rear quadrant surface, select Feature, Create, Surface, New, Advanced, Done, VarSecSwp, Done.

Select NrmOriginTraj, Done. (Window opens.)

For the ORIGIN TRAJECTORY, Use SelectTraj and pick near the bottom of CURVE_1. The arrow indicates the direction in which the sweep will be created and should be pointing upward.If it’s not, change it now using the start point command in the features box. (Done Select, Done).

For the X-TRAJECTORY, Use SELECT TRAJectory and pick near the bottom of CURVE_SIX. (Done Select, Done).

For the ADDITIONAL TRAJECTORIES, Pick CURVE_4. (Done Select, Done) and CURVE_5 (Done Select, Done).

And (Done). The Attributes window should open next. If it doesn’t, try redoing your curve selections and checking your curve alignments.

For ATTRIBUTES, select Open Ends, Done. This should drop you into the Sketcher Mode to create the sweep section.

Figure 7a. Left-rear surface.		Figure 7b. Section for the left-rear surface.

Sketch a curve through points (the lazy S icon again) from the bottom of CURVE_6 to the bottom of CURVE_5 and on to the bottom of CURVE_4 (shown in purple).

Use centerlines perpendicular to the RIGHT and FRONT datum planes to create tangency constraints, as shown. Be sure the points on the curve align with the ends of the existing curves.

Exit sketcher and select OK to see the surface.

If you have had problems with this step, try to simplify your profile curves and use straight lines instead of a curve in the projected section. You may find it easier to redefine things after they have been created rather than trying to get them perfect the first time.

For the left-front surface (Fig. 8a), create the surface the same way using another variable section sweep similar to the left-rear surface, except this time use CURVE_1 for the ORIGIN TRAJectory, CURVE_2 for the X-TRAJECTORY and CURVE_ 3 and CURVE_4 for additional TRAJECTORIES (Fig. 8b).

Figure 8a. Left front surface.		Figure 8b. Section for the left-front surface.

Step 3. Create the right-side surfaces by MIRRORing the two left-side surfaces.

Choose Feature, Copy, Mirror Dependent, Done.

Select the two left-side surfaces (Done).

For the plane to mirror about, select datum plane RIGHT (Done).

Figure 9. All four surfaces.

To hide the joint line between the two face surfaces, use Create, Surface, Merge. Select the front-left face surface and the front-right surface, and pick Join in the popup box. Select OK.

Figure 10. The merge.

Your model should now look like Figure 11.

Figure 11. The completed model.

Later you can add a bottom surface and additional merges to create a quilt that you can fill with a solid protrusion and otherwise manipulate.

Step 4. Now make the smaller head.

Create the smaller model using the same technique as above, but with only three curves in the face section. Eliminating the front-corner profile creates a face with a more pointed chin.

Create the five curves as before, this time using about 14 points each. Remember to use align and tangency constraints where applicable.

Figure 12. The curves.

Figure 13. Origin trajectory.

Figure 14. Front profile.

Figure 15. Side profile.

Figure 16. Three-quarter profile. CURVE_4 is created on a datum plane 45 degrees from the SIDE datum plane.

Figure 17. Rear profile.

The surface feature for the left-rear surface is constructed the same way as on the large head. The surface feature for the left-front surface is constructed similar to the left rear surface using only 3 curves.

Step 5. Same as Step 3 for the larger head.

Figure 18. Both models in an assembly.

A future article will illustrate how to do faces.

John Driscoll is a contract engineer available nationally and can be contacted at jjd_contractor@yahoo.com or (617) 922-6423.