A Bob’s machine, like many of the lower cost smaller machines, runs GRBL which is a machine control software running an a very inexpensive single board computer called an arduino. Usually the stepper drivers are small daughterboards that plug in to the arduino which limits them to relatively low voltages and current capabilities, so limits the stepper torque, although separate stepper drivers can also be used. These all come from the 3D printing world where they work relatively well, as the print heads are light, and there are no cutting loads. These smaller machines generally also use a cogged belt drive system which is also better suited for the lower loads of a 3D printer (or laser). These parts have enabled the creation of some low cost machines (you can buy a postcard sized cut area 3018 machine for under $200) which can be used for an introduction to CNC machining, but are really impractical for most woodworking projects, which I assume most here are interested in.
The GRBL based machines rely on a computer running a “sender” program like UGS, or picsender. They send the g-code file, line by line, to the arduino to execute. There are other programs, like easel or carbide create, that act as both design/toolpathing software and do the “sending” function. This is were most of the “free” software exists, and is functional, but not as sophisticated as the VCarve Pro software ($700) used in the Mark Lindsay videos. He also uses Aspire ($2000) for some videos, which has even more functionality. This kind of software allows you to create the g-code files that can be used by almost any CNC, including the GRBL based ones.
The trouble comes when you start learning about feeds and speeds which is important to the quality of the actual cuts. Every bit has a “sweet spot” where it leaves the best finish, and good tool life. This sweet spot also depends on the material you are cutting, hard or soft wood, ply, mdf, acrylic will all need different feeds and speeds. If you have ever routed or cut cherry, you may have experienced burning from going too slow. Similarly, with a CNC router, you need to be able to cut at appropriate speeds, with appropriate rpm rate of your spindle. If you move too slow for the spindle rpm, you will get burning (fires are possible). The bits get hot, which leads to shorter bit life (dulling). Many of the GRBL machines, with low powered steppers, are limited in their feed speeds, and often use routers with limited speed ranges. The Bob’s is particularly prone to this, as it uses a fixed speed (30,000 rpm) drywall cutout tool for its spindle, and is fairly limited in feed rates (20 ipm is the recommendation by “Bob”). This of course also makes jobs take much longer. A cut I can do on my machine in 10 minutes might take 2 hours on a Bob’s.
