SolidWorks 2011 Parts Bible - Matt Lombard [315]
Figure 24.12 shows the difference between Parting Line draft and Step draft on a simplified part. The image on the left is the Parting Line draft. The middle image is Step draft, where a ledge is only created on one side of the parting line. The image to the right is essentially double Step draft, where the total step size is minimized by distributing it across both sides of the stepped parting line.
The draft in these images is slightly exaggerated to make it easier to see.
The workflow for Step draft is as follows:
1. Start with a part that has a stepped split line, where the angled line makes angles of more than 90 degrees rather than less than 90 degrees.
2. Create a plane that defines the direction of pull and is located at the level of one of the split lines (for single Step draft) or at the midpoint of the angled line (for double Step draft). The location of the plane will determine the “pivot” point for the drafted faces. Essentially the line of intersection between this plane and the drafted face will remain stationary and the rest of face will pivot around it.
3. Initiate the Draft feature, and set the option to Step draft. Consult your tooling people about whether to use tapered or perpendicular steps. Perpendicular are probably easiest to tool.
4. Select the edges of the parting line. Make sure that the yellow arrows indicate which faces you want to apply draft to.
FIGURE 24.12
Comparing Parting Line draft to Step draft
Step draft can only draft faces on one side of the parting line at a time. To draft the faces on the other side of the parting line does not require another Step draft feature. You can use a Neutral Plane feature, using the plane created in Step 2 as the Neutral Plane. It will maintain the steps created by the Step draft feature.
Some draft limitations
One important limitation of draft in SolidWorks is that it cannot draft faces in both directions in the same feature. For example, if you have a parting line on a part, you must first draft the faces on one side of the parting line, then the faces on the other side of the parting line. This results in two separate draft features rather than one, and is simply an inconvenience.
Another inconvenience that affects many features in addition to draft is that you can only draft faces from a single body at a time — an understandable limitation, but annoying and inconvenient.
The biggest limitation is that you can't draft a face if it has a fillet on one of its edges that runs perpendicular to the direction of pull. To get around this, you usually have to tinker with the feature order. On imported parts you might have to use FeatureWorks to remove the fillet or Delete Face to reintroduce the sharp corner.
You may sometimes find that draft does not work if you do not draft all faces that are tangent to one another. This is the situation where the fillet is on an edge that is roughly parallel to the direction of pull.
What to do when draft fails
Part of the key to success with the Draft feature is that you have your expectations aligned with the actual capabilities of the software. If you recognize a situation where the draft can not work, you may be able to correct the situation by changing feature order, combining draft features into a single feature, breaking the draft into multiple features, or changing the geometry to be more “draft friendly.”
Sometimes the Allow Reduced Angle option can be used for Parting Line draft. If you use this, follow it up with a draft analysis to make sure that you have sufficient draft in all areas of the model. This option enables the software to cheat somewhat in order to make the draft feature work. The SolidWorks