A Buyer's Guide to Benchtop CNC Machines
As CNC machines have grown in capability and popularity, they're finding their way into more and more home shops. With small footprints and relatively low price tags, benchtop CNCs—essentially robotic routers—provide a good way to dip your toe into the "tech" side of woodworking. If you're intrigued by the idea, but don't know a gantry from a spindle, we'll help you understand the important things to look for in a CNC.
First, determine your budget
Benchtop CNC units sell from about $1,500 to $6,000, with many variables that affect pricing. As with many tool purchases, first decide not only how much can you spend, but also how much should you spend? In other words, what will it take to get a machine that will do what you need it to do? Remember this adage: "Buy the best and you'll only cry once." Precision, tight tolerances, and durability typically add cost. A low-cost machine may not give you the performance you need, adding frustration and buyer's regret. And as technology changes—both with the CNC software and the computers required to operate them—your setup might become less nimble or effective over time.
Pick the appropriate envelope
Like any machine, a CNC unit has a given workpiece capacity, called its "envelope," expressed as the maximum travel in the X, Y, and Z axes (photos, below). So your next buying-decision line in the sand is, what do you want to make? Will you be carving small signs or cutting out cabinet parts? Understanding how you plan to use your CNC determines what capacities the machine needs.
The bed on the machine in the first photo below provides a 24×24" envelope in the X and Y axes. However, that doesn't limit workpieces to the size of the bed. Although the gantry supports limit size in the X direction, the Y capacity is effectively limitless, thanks to tiling.
CNC tiling allows you to machine a portion of the workpiece—a "tile"—then slide the workpiece, machine another tile, move the workpiece, and so on (photo, above). You're limited only by the length of the workpiece you can support as it extends beyond the CNC. Dowels bored into the spoilboard and workpiece (the sacrificial MDF on the machine bed used to avoid cutting into the metal bed) register the location of the workpiece to align the tiles. Although tiling your work does extend your workspace, I wouldn't want to do it all the time. First, creating the tiling toolpath requires more work than creating a standard toolpath, and then registering the workpiece on the CNC can get fussy. If you plan to routinely cut long parts, get an envelope large enough to minimize tiling.
The Z axis defines the vertical travel of a cutter. As you look at this specification, keep in mind that the router bit or cutter and the space needed for it to travel over the workpiece reduce the Z-axis capacity (photo, above). So cutting completely through 1-1⁄2"-thick material requires Z-axis travel of 3-1⁄4" or more. And if a machine doesn't come with a spoilboard, remember that adding one reduces the stated Z-axis travel by that board's thickness.
Plot your work plans
Carving ordinary wood plaques and signs with large letters and numbers demands less precision than creating a detailed image (photo, above) or cutting out project parts that need a precise fit. Give yourself permission to buy a machine that offers less precision if the work you'll be doing doesn't demand tight tolerances.
Allow for future growth
This might be the hardest part: anticipating how you'll use your CNC in the future. Today's simple work may grow into projects that require tighter tolerances. Will you develop the need to cut larger pieces? The X-Y travel on benchtop machines varies widely. Large signs, door panels, and cabinet parts require a larger-format CNC.
Some benchtop machines can do work in a fourth axis: rotation (photo, above). This allows you to create almost any round, cylindrical, or spiral piece, such as table legs or chess pieces, that you'd make on a lathe. If you might want this in the future, buy a machine now with the capability to add this accessory later.
Obviously, down the road you can just buy a larger machine, and that might not be a bad thing as technology improves and prices decrease. You may pay the same amount in 5 years for a larger, more capable machine as what you pay for a lesser-equipped model today. (As with all technology, or having children, you just have to jump in at some point—there might never be an ideal time.)
How a CNC fits in the shop
As you consider adding a CNC to your shop, consider how well your shop will accommodate this new tool (photo, above).
■ Power requirements: Benchtop CNCs come prewired for either 110 or 220 volts, with varying amperage requirements. Make sure you have a power supply that meets or exceeds the needs of the machine.
■ A stand or bench: Some manufacturers offer stands for their machines, but not all do. You can also custom-build a stand. A bench or stand on casters allows you to roll the machine out of the way when not in use.
■ Dust collection: I would not run a CNC without some type of dust collection. A large shop vacuum suffices for most benchtop units, but the dust can quickly clog the vac's filter, reducing its effectiveness. A dust collector, with higher airflow (CFM), usually works better. You might get a dust shroud (photo, above) with the machine; if not, they typically sell as accessories. Like other tools in your shop, the shrouds typically accept 2-1⁄2" or 4" hose.
Sample the software before buying
Most CNC companies recommend VCarve Pro ($699) or VCarve Desktop ($349) for designing projects and creating CNC toolpaths. The software sometimes comes with the machine, but not always. Some companies have their own machine-specific design and toolpath software. Check before buying your machine so you know if software adds expense. Most software requires a Windows operating system, but some will run on a Macintosh system using Parallels software.
Check your comfort level with using CNC-related software before investing in a machine. Test drive the VCarve software by downloading a free trial from vectric.com. When you design projects, nearly any clip art can be turned into a file you can cut with a CNC. You also can purchase a huge variety of 3-D files at Design & Make (designandmake.com).
Features to consider
As you evaluate benchtop CNC units, you'll find a variety of "function" choices in motors, drive types, computer hardware, and more. Let's sort these out.
Router or spindle?
A CNC machine uses one of two methods to spin the bits: a dedicated spindle (photo, above) or a router (photo, below). Let's look at the differences between the two.
- Quieter than a router
- Torque remains consistent throughout its speed range.
- Spindles usually produce less runout than a router, allowing for greater accuracy.
- Typically, a spindle has an infinitely adjustable speed range of 0–24,000 rpm. The ability to drop below 12,000 rpm—the bottom end for most routers—proves better for cutting nonferrous metals.
- Spindles typically come with ER-style collets (see Spindle collets make accuracy more achievable, below); available size depends on the spindle.
Spindles can be water-cooled or air-cooled. On some water-cooled systems, the water pump automatically turns on and off with the spindle. On others, you must manually turn the pump on; forgetting to do this can damage the spindle. Any water-cooled system is self-contained, so there's no risk of the coolant getting on your work. I prefer an air-cooled spindle or a completely automatic water-cooled spindle.
- Costs less than a spindle
- Torque can vary through the speed range, which might not be a problem (until it is). Compensate by making shallower cuts.
- Some CNC machines use a trim or compact router (1-1⁄4 hp or less) rather than a more robust midsize router. Unlike trim routers, midsize routers include electronic feedback to maintain spindle speed, and collets that accept 1⁄4"- and 1⁄2"-shank bits; 1⁄2"-shank bits are less prone to breakage.
A router-powered CNC machine works fine, but given the option and budget, go with a spindle for higher accuracy and longer life.
Get turned on (and off)
If you get a machine with a spindle, it almost certainly turns on automatically when you start a toolpath and turns off when that toolpath ends. Some router-based machines include auto on/off, while others offer an optional control box to do this.
Turning a router on and off manually each time you start and stop a toolpath isn't a deal-breaker, but you must remember to turn it on before beginning the toolpath or you'll likely break the router bit and damage your workpiece. I much prefer doing whatever it takes to have auto on and off.
Spindle collets make accuracy more achievable
Routers in CNC machines use the same collets that you find on any router. However, most CNC spindles use ER collets. What's an ER collet? The E is a holdover from naming items with a letter series, while the R is for Rego-Fix, the company that made the collet self-releasing. ER collets get machined to tighter tolerances than standard router collets. This might prove a huge factor when you're trying to do precision work. When evaluating spindles, opt for ER collets when available.
Drivers, move your bits
When it comes to moving the spindle or router in the X, Y, and Z axes on a benchtop machine, you have three choices: belt drive, lead screw, or ball screw.
■ Belt drive: Cogs on the pulleys prevent belt slippage, but as you use the machine, dust in the cogs might interfere with the belt engaging. Wide belts, such as the 15mm one shown in the photo above, work more effectively than narrow belts. A belt won't develop surface rust like lead or ball screws can. Belt systems typically move the bit position faster than screw systems, but don't handle heavy loads as well. As long as you use the system within its capabilities, you'll be fine.
Belts can stretch, potentially affecting accuracy, but if one does stretch or break, it's easy to replace. Realistically, a belt can last a very long time and be tightened if it does stretch a little.
■ Screw drives: With both types of screw drives, the screw transfers the rotary motion of a motor to the linear motion required to move in the X, Y, and Z axes. A screw system works similarly to a threaded rod and nut: Imagine the nut captured in a housing on the CNC. As the screw turns, the captured nut moves the spindle or gantry (the bridge to which the spindle mounts).
The threads on a lead screw (photo, above) feature slightly rounded edges, quite different from a threaded rod, and purpose-designed for the loads caused by movement. The threads engage with a self-lubricating nut with wear compensation built in.
A ball screw nut (photo, above) contains ball bearings that roll in the concave recesses of the screw. Ball screws enjoy an edge in accuracy over lead screws, thanks to less backlash. Most ball screws require manual lubrication, though they create little friction and work very efficiently. This translates to long life and good transfer of power from the motor to the screw to the router bit.
All of these systems work, but given the choice, opt for a ball screw system.
Motor choice drives cost
CNC motors come in two types: stepper and servo. A stepper motor (photo, above) operates on what's called an open-loop system. This means the software sends a signal to the motor to move, and it assumes the motor did what it should. A servo motor operates on a closed loop. In this case, the system sends the signal to the motor to move, and then double-checks to make sure the correct move happened. Servos provide a better approach, and you'll see them on large-format CNCs, but rarely on benchtops. So if you want this option, be prepared to pay at least $10,000 for a larger machine.
The brains of the operation
Once you create your project design and toolpath, that information gets transmitted to the CNC via a fob (also called a pendant). Or, you may have to plug a computer directly into the machine.
The CNC typically connects to your computer via a USB port. Many users build a cabinet for the computer to protect it from the dusty environment. On the Shapeoko CNC (photo, above), you can do other tasks on the computer while it's running the toolpath, which I prefer. With some CNCs, the computer "locks up," meaning for the duration of the cut you can't use the computer for anything else. It doesn't take much of a computer to run the CNC, so if you go this route, shop for an inexpensive new or used computer and dedicate it to the task.
If the CNC has a fob, you'll do your design and toolpath work on a computer, save the toolpath to a flash drive, and plug that flash drive into the fob (photo, above). Regardless of whether you use the computer directly or a fob, functionality is very similar. You use the device to zero your axes, control the speed of travel, and set up the machine.
Get in touch with the bit
Every time you put a new bit in the collet or use a different thickness of workpiece, you need to teach the bit the height of the wood surface, a process called zeroing the Z axis (photo, above). The touch plate may come with the machine or be an accessory. It's definitely worth having.
Do lots of research in advance
Honestly, it's always difficult to give tool-buying advice, and even more so with CNCs. The ideal bottom line: Buy your last tool first. Evaluate your CNC goals and use those to narrow your search, keeping future growth in mind. Look for and attend a CNC user group in your area or online so you can talk to people about their machine choices and experiences and get real-world practical information. Look for CNC classes in your area and tire-kick machines before you buy. If possible, attend a trade show where you can visit with multiple manufacturers and see firsthand several machines.
About the CNCs featured in this article
Designed and built with big-time features and performance, but at a smaller scale. Axiom also sells machines in other sizes. The Iconic CNC machines do not accept a fourth axis, but their Pro series machines do.
- X-axis travel 23.8"; Y-axis travel 24.1"; Z-axis travel 3.9"
- 1-hp air-cooled spindle
- 1⁄4" and 1⁄8" ER collets
- Auto on/off spindle
- Ball screws throughout
- Fob included
- Z-axis touch plate included
- Optional dust shroud
- No CAD/CAM software included
This is a very capable machine with a large work envelope, and includes Shapeoko's Bitsetter touch plate. Unlike other Z touch plates, Bitsetter also locates the corners of your workpiece for the X-Y origin.
- X-axis travel 33"; Y-axis travel 33"; Z-axis travel 4"
- Router not included; accepts any trim router with a 65mm-diameter motor, or purchase Shapeoko's optional 1-hp Carbide ER-11 compact router, which includes 1⁄4" and 1⁄8" ER collets.
- Requires purchase of Bitrunner accessory for auto on/off
- Belt drive on X and Y axes. Lead screw on Z axis
- Requires a computer with OS/X 10.14 or higher operating system or Windows 8, 10, or 11 (Intel or AMD processor).
- Optional Z touch plate
- Dust shroud included
- Carbide Motion software included; this software runs the CNC and must be installed on the computer used with the tool.
- Carbide Create 2-D CAD/CAM software included for designing and creating toolpaths
- Cannot accept a fourth axis
Next Wave Shark HD500
All Next Wave machines (except the SD100) come with their Virtual Zero Unlimited software. This cool technology allows you to map 3-D surfaces so you can then machine over that surface, such as adding lettering toa rounded surface. Virtual Zero lets you do that without creating a 3-D model.
- X-axis travel 13"; Y-axis travel 25"; Z-axis travel 7"
- Router not included; accepts 31⁄2"-diameter router motors, such as the Bosch 1617, DeWalt DW618, or Porter-Cable 890 series (optional 2-hp water-cooled spindle)
- Auto on/off for router
- Lead screws throughout
- Fob included
- VCarve Desktop included
- Must provide your own spoilboard
- Accepts a fourth axis
- Optional Z touch plate
- Optional dust shroud
Portable CNC: The Next Gen
Shaper Origin (shapertools.com) is a handheld CNC worth considering. This portable CNC—about the size of a 3-hp plunge router—allows you to take the tool to the work instead of the work to the tool, fits in a toolbox, and can store under a workbench when not in use. Origin orients itself to coded "domino" tape applied to your workpiece (photo, above), so you have virtually no X-Y limitations. This means you can easily CNC-carve in the middle of a large workpiece—something next to impossible on a benchtop CNC. You run it hands-on, tracking the bit location on the toolpath using the built-in screen. Origin makes minor corrections to the bit location to stay on the toolpath. Because it looks and operates like a handheld router, it feels more like "real" woodworking. With a conventional CNC, you push a button and do other work while it cuts.