Sienci Labs AltMill MK2 4x4
$4,290 (4x4), $6,190 (4x6), $10,390 (4x8)
Pricing last checked February 2026
Our Take
The AltMill is Sienci's answer to "what comes after the LongMill?" It's a serious production machine disguised as a hobbyist CNC. Ball screws, linear rails, closed-loop motors, and 600 IPM speeds put it in light-industrial territory. At $4,290 for the 4x4, it competes directly with OneFinity's top-tier machines and wins on features (closed-loop alone is huge). The caveat: spindle sold separately adds $800-1,500+. This isn't a weekend warrior machine, it's for people running small CNC businesses or serious makers who need repeatable, professional results. Sienci's gSender software and community support are top-notch.
Sienci Labs AltMill MK2 4x4 Specs
- Price
- $4,290 (4x4), $6,190 (4x6), $10,390 (4x8)
- Status
- Active
- Work Area
- 49" x 49" x 5.5" (4x4), also available in 4x6 and 4x8
- Frame
- Custom-designed machined aluminum extrusion with HGR15 linear guides
- Drive System
- Ball screws on all axes
- Linear Motion
- HGR15 linear rails (industrial-grade)
- Motors
- Closed-loop stepper motors on all three axes
- Controller
- SLB-EXT controller with emergency stop
- Spindle
- 80mm spindle mount (spindle sold separately - 1.5kW, 2.2kW, or 2.2kW ATC options)
- Collet
- Depends on spindle (ER20 for 1.5kW/2.2kW options)
- Max RPM
- Depends on spindle (typically 24,000 for air-cooled)
- Enclosure
- None
- Assembly
- Partially pre-assembled; detailed assembly video and resources available
- Software
- Compatible with gSender (Sienci's free CNC control software), Vectric, Carveco, others
What Stands Out
- • Production-level cutting speeds (~600 inches/minute)
- • Closed-loop motors auto-correct positioning and auto-stop when necessary
- • Low maintenance design for production work
- • Y-axis auto-squaring; limit switches by default
- • Tram adjustment capabilities
- • Cuts hardwoods, plastics, foams, composites, aluminum, even steel
- • Footprint: 59" wide x 62" deep (4x4)
- • Sturdy metal legs with shelving capability underneath
- • Inductive sensors for homing
- • Ships within 2-3 weeks
What the Community Says
Extremely well-regarded among serious hobbyists and small business owners. Users praise the rigidity, speed, and closed-loop reliability. The "pinnacle of hobby CNCing" tagline isn't marketing fluff. Some sticker shock at the price, but consensus is "you get what you pay for." Sienci's reputation for customer support carries over from the LongMill. Frequently mentioned as "the machine I wish I'd bought first" by people who upgraded from cheaper options.
Free Sienci Labs AltMill MK2 4x4 Feeds & Speeds Calculator
Skip the guesswork. Open our calculator with the Sienci Labs AltMill MK2 4x4's specs pre-loaded and get safe starting RPM, feed rate, and depth of cut for your bit and material.
Open the Calculator →Compare the Sienci AltMill
Other Machines to Consider
Guides for New Buyers
Own a Sienci Labs AltMill MK2 4x4 or thinking about one?
One email a week: real owner findings, feeds and speeds that work, and new free carving files.
Free. No spam. Unsubscribe anytime.