How tall should I make my 3D relief for the thickness of board I have?

What the software requires

The only hard rule in the official documentation is that the thickness of the model must be less than the thickness of the material. The Material Setup form reports the current figure in the Model Thickness field and lets you place the model in the block with Gap Above Model or Gap Below Model. The documentation does not give a ratio of relief height to board thickness. That part is judgment.

What educators suggest

• One published relief guide suggests 8 to 10 mm of relief on a 20 mm panel, 10 to 12 mm on a 25 mm panel and 6 to 8 mm on 18 mm MDF, and warns against going past about 60% of the material thickness.
• Another published guide gives the example of 3/4 inch stock with a 1/4 inch base left under the carving, which leaves a maximum relief of 1/2 inch.

Both land in the same place: roughly half the board for the relief, with solid material left underneath. Treat these as starting points and test on scrap.

Steps

1. Build the model without worrying about final height.
2. Open Material Setup and read Model Thickness.
3. If it is too tall, click Set... beside Scale Model Height (or use Scale Model Height on the Modeling tab, then Set Exact Height...) and type the height you want. This scales the whole composite model at once, so you do not have to change each component.
4. Check the 3D View. If the model now looks squashed, in Aspire see the entry on the Emboss Component tool, which is meant for lowering tall imported models while keeping surface detail.
5. Position the model with the gap fields. Double-clicking the three marks beside the slider places it at the top, center or bottom of the material.

Pro tips

• To get more apparent depth from a thin board, recess the subject. The official 3D sign tutorial (an Aspire tutorial) models a smooth dish in the center of the sign specifically to make the best use of the material thickness.
• The Shape Height slider in Component Properties takes its range from the material thickness. If the range looks wrong, fix the thickness in Job Setup first.
• Taller relief means more roughing and a longer reach for the finishing tool, so only add height that the design needs.