On October 22, 2025, Sienci published a long post about the AltMill 4×8 and said preorders open October 29. The machine-only price starts at $7,490 USD, or $10,390 CAD. The spindle is extra. This is the AltMill stretched to a full sheet of plywood, the size cabinet shops and sign shops actually buy material in.
Sienci is the Waterloo, Ontario company behind the LongMill and the smaller AltMill. The AltMill has been the stiffer sibling, with ball screws and a spindle mount for people who outgrew a trim-router gantry. A 4×8 is a different kind of object. Sienci says Y travel is just over 8 feet, the long axis is a joined rack and pinion, and the machine weighs several hundred pounds.
TMWB has not tested the AltMill 4×8. Everything here comes from Sienci's October 22 post, and the claims are Sienci's.
How much room does it need?
Sienci puts the footprint at about 114 inches long, 66 inches wide, and over 66 inches tall once a spindle is mounted. That's 9 feet 6 inches by 5 feet 6 inches of floor, before you leave an aisle for carrying sheet goods. The height figure includes a spindle you still have to buy. I'd tape that rectangle on the floor and check it against the garage door track and the overhead lights before ordering.
Just over 8 feet of Y travel lets a full sheet stay clamped for one complete job. On a shorter machine the workaround is tiling, where you cut one region, slide the panel, and blend the next toolpath (the route the cutter follows) into the first.
Why a rack and pinion instead of ball screws?
Ball screws are accurate and common on the smaller AltMills, but they're a poor way to build an 8-foot axis. Long screws sag, and you can't cut one in half, mail it, and expect the two halves to act as a single screw. Sienci says the long axis is rack and pinion so it can be joined and so a courier can deliver the crates.
A rack and pinion drives a round gear (the pinion) along a straight toothed rail (the rack). It's the usual way to move a full-sheet gantry. The gearing is about 5:1, meaning the motor shaft turns roughly five times for each turn of the pinion. That reduction multiplies torque and moves the gantry more slowly than the motor spins. The post pairs the ratio with no feed rate and no pushing force, so I read 5:1 as a description of how the motor is geared to the rack.
Every long pass rolls the pinion across the seam where the racks are joined. A gantry this long will also flex more than a desktop. Deflection is the distance the structure bends when the cutter pushes on it. Sienci shows that bend in a diagram and prints no measured miss at the seam.
What does Sienci say about ordering?
The post is blunt about a few things buyers usually learn too late.
- There's no practical upgrade path from a 2×4 or 4×4 AltMill to this frame.
- A 5×10 isn't on the schedule.
- Batch 1 is about 150 machines, with shipping estimated from mid-February to early March 2026.
- You pay in full up front, and Sienci says you can get a full refund before the machine ships.
- Courier freight inside North America is estimated at $300 to $500 USD.
- Wood and plastic are the materials Sienci talks about first.
What about power and software?
The machine runs on 110 VAC (volts of alternating current, which is ordinary wall power) at up to about 500 W, and that rating covers motion only. Five hundred watts is a small-heater load for the axis motors and controls. The spindle, the motor that spins the cutter, sits outside that figure. Many people will want 220 V, a higher-voltage circuit, for the spindle. If the wall where you'll put this has only 110 V outlets, spindle shopping includes an electrician.
gSender, Sienci's free sender software, is supported. A sender streams G-code (the text list of moves, speeds, and tool calls) to the controller.
What was the tool changer teaser?
In the same post, Sienci teases an automatic tool changer. The details it gives are roughly $2,500 to $3,000, ISO20 tool holders with ER20 collets, up to 12 pockets, a 220 V 2.2 kW air-cooled spindle, and a normal shop compressor.
ISO20 is the taper, meaning the cone on the holder that locks into the spindle nose. ER20 is a collet series, the split sleeve that grips the cutter shank. A pocket is one parking spot, so 12 pockets is a rack of up to a dozen tools. A kilowatt is 1,000 watts, which makes the spindle 2,200 watts, cooled by a fan. The compressor is on the list because this style of changer uses air to release the holder.
That teaser isn't the tool changer launch. Prices and kit contents get their own post later. If you order on October 29, you're ordering a router, and the changer is a promise of a November announcement.
How does it compare with other options?
In October 2025, the full-sheet routers people already know include machines like Avid CNC's or a Onefinity with a custom table, plus Shapeoko and LongMill owners who tile a sheet because their machine is 4 feet wide. The AltMill 4×8 is Sienci's answer at a machine price under $8,000, before the spindle, the freight, and the dust collector you'll want the first hour you cut birch ply.
Who is it for, and what's unknown?
The post doesn't settle which spindle you should buy, how accurate the machine is once the rack is joined, or whether batch 1 holds its February window. One hundred fifty machines isn't a warehouse full of stock.
If your shop already cuts 4×8 sheets and you have 220 V available for a spindle, this is the Sienci to read before October 29. If you're in an apartment, or you mostly cut cutting boards, the LongMill is still the machine with your name on it.
Sources and image credits
- Everything you need to know about the AltMill 4×8 (Sienci Labs)
- Sienci AltMill line
- Product images: Sienci Labs announcement post
