Solidworks Plastics Features: Draft

Draft is really the workhorse of the Solidworks plastic features. It can handle a lot of situations, and maybe even some you’re not aware of. I was responsible for getting some of the more obscure functionality put into the software because as a reseller application engineer one of my customers was the old Delphi that made a lot of GM parts.

Remember that when working with plastic parts, the default condition is that draft should always remove material from the part. It’s just a good rule of thumb. You won’t get struck by lightning for not doing it, but you should be ready with a good reason if you don’t.

Draft Analysis

One thing you might consider doing when building or working on plastic parts is to set up the Draft Analysis early on and just work with it turned on. When you do this, all the new faces you create will automatically be colored according to the draft analysis. This is a very handy way to work. You never have to guess about the draft.

Draft In Extrude

The first and easiest kind of draft is just the draft in the Extrude feature. Sometimes this is what you need, and sometimes its not. If you use this, you’ve got drafted faces on your solid right from the beginning. This sometimes makes things more difficult. Many time people wait until the end (before the fillets) to add draft as separate features.

You can set up the draft in each direction all in a single feature

Also don’t forget about the Draft Outward option. Sometimes it’s just exactly what you need, although not always.

Draft as a Separate Feature

When you apply draft as a separate feature, things can get more complicated, but it also allows you more control. One of the situations that might occur is the need for several different Draft features. Solidworks has added some functionality here in recent years with a Direction 1 and Direction 2 draft, and this does cut down on the number of features you have to create, and speeds up your work a bit.

Draft as a separate feature enables you to add different types of draft:

Neutral Plane: Creates draft such that draft is added based on distance from selected plane. This can use a Direction 1 and a Direction 2 setup.

This refers to the red and green faces on the near end of the part shown to the right. (yellow faces are for the next example).

Parting Line: Draft can be added to indicated face starting from a selected edge. Sometimes you have to use a Split Line to add this edge to the model. This can use a planar PL (shown on the right) or a non-planar PL (on left). This can also use Direction 1 and 2.

This works like the fancy Step Draft option, but it is simpler to set up, and it breaks up the faces, and may be much more difficult to machine.

Step Draft: This is a special kind of draft used when the split line is not just a single straight line. It creates a mismatch at the PL, but it leaves the face unbroken.

The Step Draft requires a reference plane to be set up at one of the parting line elements, as shown below. This type of draft does not allow Direction 1 and 2, only Direction 1.

Also, you have to make sure that the little yellow arrows are pointing to the correct face to draft. Unfortunately, yellow is also a color used by the Draft Analysis, so you can’t see the yellow arrows in these screen captures. The yellow arrow denotes the side of the PL to draft, and the gray arrows denote the direction of pull.

On very complex PLs, sometimes not all the arrows point the right direction, so you have to use the Other Face option in the PropertyManager.

Other Types of Draft

Infrequently you may have to sweep a sliver triangle around a part to add draft. This would be the case if you wanted draft that didn’t give just straight sides.

You may also have to simply model in draft with lofts if you can’t deal with any of the standard draft functions.