Sienci Labs AltMill MK2 4x4

About the Machine

The AltMill MK2 4x4 is Sienci Labs' large-format CNC, built on a machined aluminum extrusion frame with a 49in x 49in working area and a 5.5in max Z-height. It uses closed loop stepper motors rated for over 600 IPM, driven through ball screws and HGR15 linear guides on all axes. It ships with an 80mm spindle mount only; you supply your own 80mm spindle or router.

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 AltMill does not come with a bundled spindle, so its top RPM depends entirely on what you mount to the 80mm holder, check that unit's own rated speed against the chart rather than assuming a number. Where the AltMill stands apart is rigidity: a machined aluminum extrusion frame, ball screws and HGR15 linear guides on every axis, and closed loop steppers rated for over 600 IPM. 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 AltMill's build is aimed squarely at that bar, so with a suitably powerful spindle mounted, you can push depth per pass further than on a lighter belt-driven kit. Even so, push too deep for your spindle 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. The AltMill has no bundled spindle, so check the RPM rating on whatever spindle or router you have mounted and use its actual number if it differs. With the bit maker's 0.025mm per tooth (0.0010 in), at a spindle speed of 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.