Sienci Labs LongMill

About the Machine

Sienci Labs no longer sells this model, but it remains fully supported in Easel. The original LongMill shipped in three sizes, 12x12, 12x30, and 30x30, each with about 4.4in of Z travel. It uses NEMA 23 steppers on lead screws, with laser-cut steel gantry plates, extruded aluminum rails, and MGN12 linear guides on Z, and it runs GRBL firmware on an Arduino board. Sienci recommended a Makita RT0700/RT0701 router (10,000 to 30,000 RPM, 1.25 HP) as the spindle.

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 original LongMill's recommended Makita RT0700/RT0701 router runs from 10,000 to 30,000 RPM, comfortably above every speed on the chart, so you can run the chart's recommended RPM directly instead of capping it. This is a lead-screw kit on NEMA 23 steppers with steel gantry plates and aluminum rails, sturdier than a small belt-driven hobby machine but still a benchtop kit, not a heavy industrial mill. 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 LongMill's build gets partway there, so take moderate passes and build up rather than assuming full-diameter depth from the start. 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, and the recommended router's 10,000 to 30,000 RPM range covers that easily, so run 16,000. With the bit maker's 0.025mm per tooth (0.0010 in): 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.