How do I make a small box with a pocketed inside and a lid that fits?

What the project is

The simplest CNC box is two solid blanks. The base gets a deep pocket. The lid gets a shallow pocket around a raised plug (a tenon or lip) that drops into the base pocket. No flip is needed if the lid is machined upside down.

Steps

1. Stock. A published heart box uses a 1 3/8 inch blank for the base and 3/4 inch for the lid. Measure yours.
2. Base vectors. Draw the outside shape and the cavity shape inside it.
3. Base toolpaths. Pocket the cavity (1 1/4 inch Cut Depth in the example, leaving a 1/8 inch floor), then Profile the outside with tabs and ramps. Deep pockets need a bit with enough cut length and several passes.
4. Lid vectors. Copy the base outline and cavity shape into the lid job. Offset the outline outward (1/4 inch in the example) to make a pocket boundary that runs past the lid edge. Then delete or ignore the original outline for pocketing.
5. Lid toolpaths. Pocket between the enlarged boundary and the cavity shape, 1/4 inch deep. The cavity shape is left standing as the lip. Then Profile the lid outline.
6. Fit. Measure the base pocket and the lip with calipers. The walkthrough aims for a lip about 0.005 inch smaller than the pocket. If it is tight, offset the lip vector inward by half the difference and recalculate. Forum makers report starting allowances of 0.002 to 0.005 inch, and that 0.5 mm was too loose.
7. Order. Machine the base first. Cut the lid second and test the base on it before unclamping, so you can skim the lip again in the same setup.

Pro tips

• Finish adds thickness. A lid that is perfect bare can bind after two coats.
• The software maker's free Heart Shaped Box does the lid as a two-sided job: decoration on top, the fitting pocket underneath.
• For hinges, measure the hardware and prove the mortise on scrap. See the entry on the Inlay Toolpath for fitted parts.