Bob's CNC Evolution 3

About the Machine

BobsCNC no longer sells this model, but it remains fully supported in Easel. The Evolution 3 is a belt-driven CNC router kit with a 457 x 406 x 85 mm working area, NEMA 17 steppers on GT2 belts on X and Y and an acme-rod Z-axis, and ships with a Makita RT0701C variable-speed router. It runs GRBL firmware on an Arduino Uno.

Cut Settings on this Machine

Every cut starts with one formula: Feed Rate = Spindle Speed (RPM) x Chip Load x Number of Cutting Edges (flutes). Chip load is the thickness of material each cutting edge removes in one revolution of the bit. This number comes from the manufacturer of the bit, which publishes a chip-load chart for each bit diameter and material. Look up your exact bit and material, start from the middle of the published range, and you have the third number in the formula. The chart below shows the recommended spindle speed for each material and bit type.

The Evolution 3 ships with a Makita RT0701C router, but BobsCNC's page for this kit does not state a maximum RPM, so check the router's own speed dial or plate before picking a spindle speed off the chart. This is a lightweight, belt-driven kit on NEMA 17 steppers with an acme-rod Z-axis, not a heavy industrial machine, so depth per pass is limited by rigidity more than spindle power. A truly rigid machine with a powerful spindle can cut as deep as the bit is wide in a single pass, but that takes real spindle torque, a drive train and clamps that hold firm, a gantry that will not flex, and enough mass to soak up vibration. The Evolution 3's belt-and-acme-rod build falls short of that bar, and the fix is simple: take shallow passes. Push too deep and the bit deflects and chatters, leaving scalloped edges, or it rubs instead of cutting and burns the material. The fastest way to dial in a cut is to see what has already worked for other people.

Worked example for feed rate: 1/8in (3.175mm) two-flute solid carbide end mill in hard wood. The chart says 16,000 RPM. BobsCNC's page for this kit does not state the router's maximum RPM, so check the Makita RT0701C's own speed dial and use its actual top speed if it is lower than this. With the bit maker's 0.025mm per tooth (0.0010 in), at 16,000 RPM: 16,000 x 0.025 x 2 = 800 mm/min (31 in/min) feed. For depth per pass, start shallow and check Community Cut Settings in Easel for what works on this machine. If the cut sounds strained, reduce the depth, not the feed. Slowing the feed below the chip load makes the bit rub instead of cut.

Community Cut Settings shows the spindle speed, feed rate, and depth per pass other makers actually run for your machine, material, and bit.