Photos by Rob Brown; Illustration by Len Churchill
You can think of a benchtop CNC machine as an inverted table router that is controlled by a computer. Instead of the router motor being under the table, it’s on the top. The router motor (in higher end CNC this is replaced by a spindle motor) moves in three directions, called the X- (front to back) Y- (side to side) and Z-axis (up and down). These determine the maximum milling limits of the machine. CNCs are often rated by the size of their milling area.
The router motor is suspended on a gantry above the work table. Stepper motors move the router motor along the X-, Y- and Z-axis. A ball screw and nut assembly (sometimes a lead screw or rack and pinion assembly) converts the rotational motion to linear movement. How quickly an item gets milled depends on both the travel speed, the speed at which the motor moves about the milling (or work) area before it begins cutting, and the cutting speed, which depends on the router speed you select, size of cutter, depth of cut, and type of material being milled. Designs are typically uploaded via a USB cable, and the CNC is controlled by means of an onboard LCD panel or hand-held controller.
Price: Kit ($500 – $2,000); Assembled ($2,500 – $10,000)
Motor: Palm router or spindle motor
X- and Y-axis Milling Area: 7″ x 9″ to 33″ x 33″
Z-axis: 2″ to 7″
Motor Travel Speed: 3/4″ to 3-1/2″ per second
The key to successful CNCing is learning how to use the software. Where feasible, take a hands-on or online course. Reach out to the vast community of online makers.
Ensure you understand the maximum and minimum routing speeds and feed rate of your machine and work within those limits.
Learn how to calculate optimal speed and feed rates and set the right cutter depth to get the best results. In general, higher speeds are for roughing, slower speeds for finish cuts, and materials of different densities require different milling speeds.
Purchase good-quality cutters from reliable sources. Begin with HSS while practicing, and then move on to more expensive but durable Carbide.
On small CNC machines there is a greater tendency for cutters to chatter, which can cause them to bend and eventually break. Use the appropriate size of cutter for the task at hand, and adjust cutting depth to avoid excessive deflection.