Design into 3D: box: fitted

From ShapeOko
Jump to: navigation, search

A project for the Design into 3D Kickstarter.

Copy of this page for discussion and with file links at:

Fitted boxes are the easiest to make on a CNC --- just two pocket cuts, one rabbet, and two profile cuts.


For a round box, the needed parameters may be as simple as:

  • diameter
  • overall height of the box
  • thickness of the box bottom and lid
  • thickness of the wall of the box

One then derives the following dimensions:

  • width of the rabbet cut (half the wall thickness)
  • depth of the cut for the box area itself
  • depth of the cut for the box lid

A further consideration is stock thicknesses --- if the thickness of the stock doesn't match that of the finished parts then it will be necessary to machine the material down to match.

The only number which cannot be specified up-front (or derived) is the tolerance needed to allow the lid to fit properly. Best practice is to cut a lid, then a box bottom, then test fit. Note that a round box and matching lid is also an excellent test of the overall squareness of the machine, and that the lid will only fit properly and match the bottom if the machine is square enough to allow it to do so, and that rotating the lid will be a further proof of that squareness.

Consider the following round box made out of 14mm thick stock:

  • diameter: 2 inches
  • height: 0.6875 inches
  • box wall/side thickness: 0.25 inches
  • top/bottom thickness: 0.1875 inches
Cncboxfitted round 2in.svg

A similar box design in OpenSCAD would be:

Designinto3d box fitted round 2x2 screen.png

The file for cutting this is simply a series of nested circles of appropriate dimensions:

Design into 3D box fitted round 2x2.svg

Note that the circles defining the box/lid interface might be adjusted by a needed clearance (half of that dimension inward for the box, half of that dimension outward for the lid).

Given a 14mm thick stock, an 0.1875 inch thick bottom and lid, an 0.125 inch tall lip, and using a 1/4" (6.35mm) endmill necessitating an 8mm or so offset geometry so as to cut the perimeter as a pocket rather than as a slot one would arrive at the following toolpaths:

Design into 3D box fitted round 2x2 cc toolpaths.png

which include the need to trim 1.3mm thickness off the stock for the bottom and 6.0625mm off the stock for the top.

which previews as:

Design into 3D box fitted round 2x2 cc preview.png

and when cut:

Cncboxfitted round open.jpeg

and closed:

Cncboxfitted round closed.jpeg

Source files:

Round box with dividers

To add dividers, and to preview them with rounded interior points/corners, one must first decide what sort of shape the pockets will be --- straight lines would be simple, so an "S" curve will be considered instead.