On May 6, 2026, Sienci published the LongMill MK3 and set preorders for May 26 at 11 a.m. Eastern. The prices are labeled approximate and may change: about $1,400 USD for the 30×30 ($1,890 CAD), and about $1,800 USD for the 48×30 ($2,430 CAD).
A beginner kit adds Sienci's AutoSpin T1 router, an AutoZero touch-off, a dust shoe, and end mills, and saves about $100 CAD (about $110 USD) versus buying those pieces separately. Shipping for the first run is estimated at mid-to-late August 2026, possibly early September. Sienci says about 1,000 machines are in production.
TMWB has not tested the MK3. Everything below comes from Sienci's announcement, so the numbers and the rigidity claims are Sienci's.
What do the model numbers mean?
A 30×30 moves about thirty inches in X and thirty in Y. A 48×30 keeps that depth and stretches the long axis to about forty-eight inches. Small signs and cutting boards fit the shorter bed. A long apron, or two parts nested in a row, is the job that wants the longer one.
The LongMill is Sienci's entry router, the machine that made the company, and the MK3 is a new gantry and not a bag of upgrade parts. Sienci says there's no practical upgrade path from the MK1, MK2, or MK2.5. An MK2.5 spindle kit can be fitted, with some loss of X travel because the spindle is larger. Other MK2.5 accessories carry over, except the dust shoe, which is built for each machine.
Why did Sienci stay with leadscrews?
The motion choice is the story. Sienci looked at ball screws and stayed with ACME leadscrews and spring-loaded anti-backlash nuts. A leadscrew is a plain screw driving a nut, and ACME is the thread shape. An anti-backlash nut takes up the slop with a spring so the axis doesn't hesitate when it reverses. Sienci's reasons are cost and the ability to offer more than one length without a custom screw for each size.
The rails are a different upgrade. The MK3 uses HR15 linear guides, which carry the gantry on balls rolling inside a profiled rail. They have to be oiled, which is a maintenance item the old V-wheel LongMill didn't have in the same way. Leave the rail dry and the guide becomes the wear part. The Y rail screws into the wasteboard, so the sacrificial sheet under your stock becomes part of the structure, and a cupped offcut can twist the axis.
What are the new motors and speeds?
The motors are closed-loop steppers, the same family Sienci already buys for the AltMill. Closed loop means a sensor tells the controller when the motor missed a step. Sienci's point is that a stall pauses the job instead of letting the machine lose steps and keep cutting the wrong shape. The May 6 post doesn't print a NEMA frame size.
Rapids go up. Rapids are the travel speed between cuts, and they aren't the speed you can bury a half-inch bit in maple.
| Axis | MK2 | MK3 |
|---|---|---|
| X and Y | 4,000 mm/min (about 157 in/min) | 7,000 mm/min (about 275 in/min) |
| Z | 3,000 mm/min | 6,000 mm/min (about 236 in/min) |
Sienci claims a 60 to 80 percent rigidity improvement and shows load tables at 25 N and 50 N on a 48×30. A newton is a unit of force, and 25 N is about 5.6 pounds of push, with 50 N about 11 pounds. Publishing those tables next to the test setup is the right way to back a stiffness claim, instead of just stating a slogan. I'm not going to turn that setup into a recommended depth of cut.
What else changed?
The controller is the SLB-LITE. Sienci also credits work in gSender and GRBL-HAL, a newer branch of GRBL, the firmware that turns G-code into motor steps.
The May 6 post credits that software with an independent fourth axis (a rotary you command on its own), auto-squaring (homing both ends of the gantry so the beam sits square), G-code editing in the sender, EEPROM (onboard memory that keeps your settings when the power goes off), and a tool-length sensor that measures stick-out.
The post doesn't publish a power supply wattage or a shipping weight. It spends that space on part count: about 30 unique components, 25 percent fewer than the MK2, T12 fasteners on every axis (a single Torx size), and assembly the company says takes under an hour, two to three times faster than the MK2. The machine is built in Waterloo, Ontario.
A Makita RT0701, the trim router many LongMills already use, fits the 65 mm mount that ships on every MK3, with an extension cable so the cord can pass through the drag chains (the hinged tracks that carry cables). AutoSpin T1 is Sienci's router, presented as the successor to the Makita. In the beginner kit it switches the router on and off and sets speed from the program. AutoZero stores Z when the bit touches a sensor, which replaces the old slip of paper.
What do the FAQ items say?
The FAQ is worth more than the headline "best entry level hobby CNC under $2000 USD," which is Sienci's line and should be read as one.
- A 30×30 to 48×30 extension isn't available at launch.
- The rear of the machine is open for tiling, which is how you cut a sheet larger than the travel by sliding the work. Watch the Y motor cable when you slide, because a lead that's slack in the first position can pull tight in the second.
- Vertical mounting is expected to be fine.
- Older LongMills keep their spare parts, with Sienci talking about three to five years of support.
How does the MK3 compare?
In May 2026 the LongMill's competition is the same as it has been. There's the Shapeoko if you want Carbide's ecosystem, a Genmitsu PROVerXL if you want a heavier 4×4-class frame with a spindle in the box, and an Onefinity Gen 2 if you want ball screws and will pay for them. The MK3's bet is that leadscrews, closed-loop motors, and linear guides are the right mix under $2,000. The AltMill remains the machine Sienci sells when you want ball screws and a bigger spindle mount.
Who is it for?
Preorder isn't delivery. August is an estimate, the prices are marked as approximate, and the rigidity percentages are Sienci's. If you've been waiting for a LongMill that homes cleanly and doesn't silently lose steps, May 26 is the morning. If you wanted Sienci to switch this machine to ball screws, they wrote down why they didn't.
Sources and image credits
- Everything you need to know about the LongMill MK3 (Sienci Labs)
- Sienci LongMill
- Product images: Sienci Labs announcement post
