CAD and Product Design: Questions Answered by Skill-Lync Experts

In plastic parts you have A, B and C surfaces because of how they are made. The material is melted and moulded into shape, so you can change thickness and add features freely.

Sheet metal is different. In deep drawing you start with a solid sheet that is stamped into shape. The part already has all its surfaces, and you only change its shape. You do not change the thickness drastically or add features. So there is no B and C surface in the plastic sense.

In a hood, the inner panel is a separate component. It is manufactured separately from the outer panel and then hemmed to it. It is not visible from outside, so it is designed for its function, without worrying about how it looks to the customer.

Plastic has the same split. Parts the customer sees, such as a door trim or switch bezel, are show parts. Parts the customer cannot see are no-show parts. For no-show parts you do not consider Class A and B and design to function.

Ribs are thin wall-like structures that add support and rigidity to injection molded parts. They are thinner than the primary walls and support those walls, as well as bosses, by running perpendicular to them.

Ribs are often used to replace thick wall sections, which avoids sink marks, warp and voids. Place ribs in a load-bearing direction, such as across long unsupported stretches of the part, instead of making a section thicker. You keep the support and rigidity you want and avoid the problems caused by thick walls.

It depends on which side the radius is on, and which side your B surface will be.

• If you add the fillet on the outer side (the outer radius R), add the thickness to the inner radius: R = r + t.
• If you add the fillet on the smaller, inner side (r), subtract the thickness from the outer radius: r = R - t.

Decide which side your B surface will be on, then add or subtract with respect to that. The Class A surface is the one the customer sees, and the surface is offset away from the viewer's eye, so the B side is the hidden one.

1. Split a curve: use the Trim Curve option in the Curves command. You can trim using a plane, a point or another object.
2. Align the view: orient the face and press F8. F8 makes the view normal to the closest datum plane. If you were working in a stretch and want to return to the sketch view, press Shift+F8. You can also right-click and drag to the left to find the Normal option.
3. Update one feature: right-click the feature in the model tree and choose Make Current Feature. You can then update the model one feature at a time.

This is usually because the gap option was not ticked when the knit surface was created.

Edit the knit surface you created earlier and check that the gap dialogue box is ticked. Then try Cut With Surface again.