How does Add Draft to Model work in Aspire and when should I use it on 3D components?

Overview

Add Draft to Model automatically adds a minimum angle to any steep or vertical walls in your 3D composite model. It is useful for preparing a model as the basis for a mold, vacuum forming tool or press die, for improving edge quality on machined reliefs, and for strengthening thin delicate features.

What Draft Does

A draft angle is a taper applied to vertical surfaces. Instead of a 90 degree wall, a drafted wall leans at the specified angle. For CNC relief work this serves several purposes:

1. Mold and vacuum forming preparation: the official documentation highlights this use. A part used as a mold or vacuum forming tool should not have vertical walls, or the formed part can grip the wall and not release. A slight taper lets it release with less force.
2. Improves machinability: a ball nose tool cannot cleanly machine a perfectly vertical wall, because the shank can rub the wall. A slight draft makes the wall accessible.
3. Strengthens fragile features: thin pointed crown points, spike tips and delicate projections are fragile. Adding draft widens the base of those features, which can make them stronger and less likely to break during or after machining.

How to Use Add Draft to Model

1. Make all the components you want to draft visible in the 3D view. You do not select components for this tool. Hidden components are not included, which is how you apply draft to some components but not others.
2. Open Add Draft to Model from the Modeling tab.
3. Set the draft angle with the slider or by typing a value. The documentation example shows 20 degrees. See the starting points below.
4. Click Apply.
5. The tool creates a new 3D component by baking the visible components and applying the draft angle across all the walls of the composite model. The new component is named to show the amount of draft added.
6. Both the original components and the new component remain visible, although the original may be hidden behind the new one. Hide the originals, or move them to a separate Level, if you want to work with the drafted version only. Keep them so you can edit later.

Two-sided jobs: the draft is only applied to the side you are currently working on. To draft both sides, switch to the other side and apply it there too.

What the Tool Actually Does

• It processes the composite model (all visible components combined).
• The resulting component does not have any wall angles steeper than the specified draft angle. It always creates a new component and does not modify the originals.
• Do not confuse it with Scale Model Height. Add Draft changes wall angles. Scale Model Height changes the overall Z scale.

Selective Application

Because the tool works on all visible components:

• To draft only certain components, hide all the others first.
• To avoid drafting the background, put the background on its own Level and hide that Level before applying draft.
• To draft only a foreground subject, hide the background, apply the draft, then show the background again.

Draft Angle Starting Points

The software does not publish angle recommendations. These are common shop figures, so treat them as starting points to test on scrap, and check with your material or mold supplier.

Heavy draft (15 degrees and more) changes the geometry substantially and can alter fine detail, so use it mainly where parts must release cleanly. When in doubt for a mold, more draft makes release easier, but preview the result.

Mold Use Cases

• Vacuum forming tools: CNC-machined wooden or MDF forms over which plastic is drawn.
• Rubber or silicone molds: pour-in-place molds for casting resin or plaster. Draft helps the cured material release.
• Sand casting patterns: patterns pressed into sand need draft so they can be lifted out without collapsing the cavity.
• Press dies: embossing leather, paper or foam. Angled walls reduce edge tearing.

With Offset Model: for mold making, apply Add Draft first to create angled walls, then apply Offset Model with a negative value to add clearance for the material being formed. See the entry on Offset Model.

Pocket draft with a tapered end mill: for simple pocket cavities with a consistent draft, a tapered end mill on a pocket toolpath makes the draft directly with the tool angle. For complex 3D shapes, use Add Draft to Model and a 3D finishing toolpath.

Crown Points and Structural Weakness

Thin crown points, decorative spires and other pointed features can snap off during routing or later handling, because a very thin tip has little strength across the wood grain. Draft widens the feature at its base, where it joins the rest of the model, while still leaving a visually distinct point at the top. Very sharp vertical features (narrow raised lines, thin walls) can change shape noticeably, because the angled faces converge. Always preview the draft before using it for production toolpaths.

Edge Quality on 3D Reliefs

For imported STL models and any component with steep outer walls, the 3D finish toolpath cannot cleanly machine a true vertical edge, because the shank of the tool can contact the wall. The simulation may look clean while the physical cut leaves a ragged or stepped edge.

Options:

1. Add Draft to the edge, for example 5 to 10 degrees, so there is a physical slope instead of a vertical drop.
2. A Profile toolpath to cut the outer boundary after 3D finishing, which handles the vertical wall directly.

Common Mistakes

• Forgetting that it works on all visible components. Leaving the background visible when you only want to draft a foreground element drafts the background too.
• Setting the draft angle too high and distorting the shape. Start small and preview before committing.
• Setting the angle so small that it is barely visible in the 3D view. It can still matter for physical molding.
• Applying draft to only one side of a two-sided job.
• Expecting Add Draft to fix resolution problems at model edges. It addresses steep walls. Pixelated edges need a higher resolution setting or a smaller job.
• Deleting the original components. Keep them (just hide them) so you can edit later.