A detailed two-sided CNC-machined Maker’s Challenge Coin built around the idea of continuing forward when things get difficult.

The front features THE OBSTACLE IS THE WAY surrounding a rocky passage with a path continuing through the obstacle toward the horizon. The reverse features KEEP GOING, with a large upward arrow breaking through layers of stone and debris.

This is a detailed 3D relief coin project, not a simple engraved design. Both sides use raised lettering, textured rock surfaces, and fine relief details designed to be CNC machined into a 40 mm coin blank.

Coin Blank Requirements

This project is designed for a:

40 mm diameter coin blank
3 mm thick
Brass or a known zinc alloy suitable for machining

These are the coin blanks I used for this project:

Coin Blanks Used for This Project – Amazon

The important thing is knowing what material you are machining. Do not use steel coin blanks or blanks made from an unknown or unspecified metal alloy.

A lot of inexpensive gold-colored coin blanks are sold without clearly identifying the actual material. Some may look almost identical to brass or zinc alloy but can machine very differently.

Using steel or an unknown alloy may result in poor cutting performance, excessive tool wear, broken endmills, or potentially ruined cutting tools.

Do not assume a gold-colored coin blank is brass or zinc alloy based on appearance alone.

Verify that your blank is 40 mm in diameter and 3 mm thick, and confirm the material before machining.

Workholding / Two-Sided Machining

This is a two-sided CNC project, with one design machined on each face of the coin.

If you want to follow along using the same style of workholding, you can use my 40 mm Coin Vise for 2-Sided CNC Milling:

40 mm Coin Vise – 2-Sided CNC Milling

The vise is designed specifically for 40 mm coin blanks and provides a repeatable way to hold and locate the coin while machining both sides.

Accurate positioning is especially important when flipping the coin for Side B so both designs remain properly centered relative to each other.

Full Project Video

Machining

Each side of the coin uses 2 machining operations.

1. Roughing Pass

Makera 3.175 mm × 12 mm Single Flute for Metal Endmill
Parallel toolpath
Removes the bulk of the material and establishes the overall 3D relief.

2. Finishing Pass

Makera Single Flute Engraving Bit for Metal — 60° × 0.1 mm
Radial/Offset toolpath
Used to machine the fine relief details, lettering, rock textures, pathway, arrow, and debris.

The same 2-operation process is used on both sides of the coin.

The parallel roughing pass removes the majority of the material before the engraving bit is introduced. The radial/offset finishing toolpath then approaches the relief from changing directions, helping capture finer detail throughout the 3D design.

The engraving bit is intended for the detailed finishing work rather than bulk material removal. Its 0.1 mm flat tip is extremely small, so allowing the larger roughing endmill to remove as much material as practical first reduces unnecessary work for the engraving bit.

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