Sienci Labs LongMill MK3

About the Machine

The LongMill MK3 is Sienci Labs' current benchtop CNC, sold in two working-area sizes: 30x30 at 32in x 32in, and 48x30 at 49in x 32in, both with 5.1in of Z-axis travel and 4.6in of clearance. It runs high-torque, closed-loop NEMA 23 steppers (1.2 Nm) on T12 lead screws with 15mm profiled linear guide rails on all axes, and it ships with a standard 65mm router mount only; router or spindle is not included. It is controlled by Sienci's SLB-LITE controller, which the manufacturer states runs grblHAL firmware.

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 LongMill MK3 does not come with a bundled spindle, so its top RPM depends on what you mount to the 65mm holder (it also supports 80mm spindles with a larger dust shoe, though that reduces cutting area). Sienci's recommended options, its own AutoSpin T1 or a Makita RT0701, both reach at least 30,000 RPM, comfortably above every speed on the chart, so with either of those you can run the chart's recommended RPM directly. This is a lead-screw kit on high-torque, closed-loop NEMA 23 steppers with 15mm profiled linear guide rails and anti-backlash nuts, 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 MK3'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. With Sienci's recommended AutoSpin T1 or a Makita RT0701 mounted, both cover that easily, so run 16,000; check whatever spindle you actually mount if it is different. 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.