All Desktop CNCs Are Not Created Equal

The CNC below is frequently compared to our ShopBot Desktop and ShopBot Desktop MAX tools. This tool is imported from China by several different resellers in North America. It is also available directly from China from the internet. Prices for the tool vary from $2,800 to $6,500, depending on the reseller. From published specs, the tools are apparently identical though they do have different decals. We thought it helpful to directly compare a few of the characteristics, capabilities, and features of this tool to the ShopBot Desktop and Desktop MAX CNCs.

Mechanicals

ShopBot Desktops and Desktop MAXs have a heavy, solid aluminum frame and a ‘dual-drive’ gantry. Dual-drive means there is a motor and drive system at each side of the gantry. Dual-drive insures that the gantry moves evenly and that it will not be deflected or racked when machining on the left or right side of the centerline. In contrast, the imported CNC has a single, center-drive screw and motor for the gantry that is positioned in the middle of the bay under the deck. This screw is attached to a tie bar that is then attached to the two ends of the gantry. With this system, as cutting moves further and further off the centerline, the gantry can be deflected or racked from the asymmetrical forces to each side of the centerline. One less motor and one less drive system helps reduce costs in the imported tools, but racking will be a source of inaccuracy that needs to be managed. The limitations will come into play with any heavy work, such as cutting or carving hardwoods or machining aluminum. It will also show up in edge quality when cutting plastics and it will make it more difficult doing precision work such as inlays, routing printed circuit boards, or carving jewelry difficult.

A second advantage of the ShopBot’s dual-drive design is that it leaves the area under the bed of the router available for other functionality. In comparison, on a center-drive tool, the tie-bar mechanism moving back and forth under the deck makes that area unavailable for other use.

For example, with the open, dual-drive of the ShopBot Desktop and Desktop MAX design, the area under the deck is available to create a full vacuum hold-down system (which you can make yourself or purchase from us). Moreover, the deck can be removed to allow machining of larger blocks of material, or to add fixturing such as that for our joint-making edge clamp (see detail below), or even to create space for something like an extra-large indexing/turning system.

We do favor using a screw-drive mechanism of some type for motion production in Desktop CNC’s. Screws provide excellent precision and virtually eliminate backlash. However, there are several options for such screws. After having experience with ball-screw systems (these employ ball-bearings inside the nut that rides on the screw) on earlier CNC tools, we chose a Teflon-coated lead screw for our Desktops, manufactured integral to the motor, along with a composite anti-backlash nut (that does not employ internal ball-bearings). The integral-screw keeps the mechanism simple and the axes aligned. In a typical ball-screw installation, couplers, universal joints, and outboard bearings must all be kept in alignment with the ball-nut – a complexity that increases the likelihood that maintenance attention to alignment will be needed. A bigger issue with the ball-screw on these tools is that lubrication with oil is required. It’s a maintenance thing, but more importantly, because the upper-gantry screw is close to the cutting area and unprotected on these small tools, the oil will attract dust and debris and clog the ball-bearings and their channels. Sure, a lot of big CNC’s use ball screws. But, there is typically protection of those screws in the form of shrouds or bellows. For our Desktops, dust simply falls off our Teflon screws as they spin.

A final mechanical issue is the spindle. We’ve noted that the water-cooled spindle on the imported tools probably won’t be a deal-breaker because it can be replaced. The rationale for the water-cooled spindle is that it is inexpensive – and that it will get you started. But water-cooling is awkward and involves the distracting maintenance of keeping a bucket of water from getting moldy and a pump clean and functioning. It makes these spindles a production liability, particularly in comparison to the air-cooled, European-style spindles that have been the industry standard for 50 years. In contrast to the imported tools, the ShopBot Desktop and Desktop MAX CNCs come standard with HSD, air-cooled, industrial spindles.

Electronics, Software, and Controls

In comparison with the very basic control system of the imported tool, ShopBots come standard with a full ShopBot controller and ShopBot Control Software. This controller is the same as on our larger tools and includes all ShopBot functionality, including expandability to additional axes and control of additional accessory functions.

A full CNC control creates opportunities to add features like a rotary indexer accessory that converts your Desktop into a turning daemon, doing carvings, ornamental turnings, and 3D objects in the round. The controller also supports other standard CNC attachments such as active, tangential, knives for cutting fiber materials. We think of our Desktop CNCs as platforms for digital productivity – with options for numerous types of manufacturing assistance and supported by a set of full and expandable controls.

The electronic control and software system that run our tools are tightly integrated with our tools because they were designed for the tools. We believe that good tools start with good mechanicals, but over the years of producing and using CNC tools we have come to believe that software control systems are equally important. Our software focus is on a control system that provides both smooth, efficient cutting and ease-of-use in production. Our recognition of the importance of software distinguishes us as the only manufacturer of affordable CNC tools that produces its own controls and software.

Our software provides smooth cutting motion and crisp acceleration. We have focused on getting high-resolution, straight-line and complex curved motion that is chatter-free with crisp accelerations and decelerations to make cutting efficient. ShopBot’s feed-rates, speeds, and accelerations are fully adjustable in the tool’s software interface and from within toolpath files.

ShopBot’s software interface is straightforward and intuitive to use. Carrying out basic tasks and housekeeping functions such as homing is intuitive. The control software runs toolpath files (part files) generated from virtually any CAD/CAM program. It can utilize files in standard g-code format (Fanuc/NIST RS274) and well as toolpath files that have been created in OpenSBP, an open-syntax CNC language (supported by most current CAD/CAM software).

You are thus able to run ShopBots with two different types of CNC files. Traditional g-code is fine for just running files output by CAD/CAM programs. It may feel particularly friendly if you are a CNC operator experienced with other tools. ShopBot’s OpenSBP option, provides a second and more ‘conversational’ language that is easy for a human to read, understand, and use. Unlike g-code, OpenSBP includes built-in programming functions (such as variables, logic testing, and looping) that make it readily programmed using friendly, BASIC-language-like expressions. OpenSBP makes it straightforward to do everything from creating a button for regularly moving a tool to a standard position, to creating production routines that will improve the efficiency of workers as they manage jobs and files and move parts through your production process.

Software That is Available and Up-to-Date

We continuously evolve our control systems and software as opportunities to add capabilities and features become available. The most recent control software for your tool is always available for download from our website, FREE. When the availability of new electronics allows us to develop improved controllers, we also make them available for older ShopBots. It is possible to retrofit our latest control cards or control box – greatly improving the functionality of a tool – to virtually any age ShopBot.

Our software provides an incredible base of learning resource for CNC. That’s because all ShopBots work the same. Information across our wide spectrum of users makes it easy to get any question answered. Check out our huge web library of free training videos and webinars. Or, look through years of information, help, and hints about fabbing with CNC in our Talk ShopBot Forum.

All our tools come with two, CAD/CAM design software packages. VCarve Pro is acknowledged as one of the easiest-to-use design tools for getting into CNC. For advanced, engineering-driven work, we provide a year’s license to Autodesk’s Fusion 360, a full design, modeling, and rendering program with integrated CAM.

Making a Benchtop CNC an Agile Production Monster!

The concept of a desktop or benchtop tool is that it is agile and portable. That for a given project, it can be put on one bench or another or put on a rolling bench and moved around the shop or factory floor. Portability is not possible if a new 220V circuit must be installed every time you want to move the tool, or if a long, heavy 220V cable needs to be dragged across the floor of your shop. Our Desktop CNCs are designed to provide the highest level of speed, power, precision, and cutting force in a tool that is connected to a standard 110VAC outlet. When you are ready to move a ShopBot Desktop or Desktop MAX CNC to another location. Do it – and, then just plug it into a different outlet. We designed and built these tools from the ground up with agility and configurability in mind. ShopBot Desktops have the power and rigidity of full-size CNC’s and they have as much spindle power as can be packed into 110V. (*If you may have been considering a CNC tool with a woodworking router, please have a look at this white paper comparing the measurement of router cutting power to spindle cutting power).  

We’re very enthusiastic about benchtop CNC tools as production assets for small manufacturing. These tools are frequently as productive as full-size tools when material size is small. They are capable of high precision and powerful cutting because, relatively speaking, they can be quite rigid. Many can double as small mills for working with aluminum and can optionally power a 4th, rotary axis for turning and 3D shaping.

In This Case, Buy American Because You Get More for Your Money

It is often believed that the cost difference between imported products and products like the ShopBot Desktop and Desktop MAX is a result of inexpensive offshore labor. It does cost a little more to build equipment in the US than offshore. But as far as our Desktop CNC tools go, the cost differences in comparison to these imported tools reflects what you are getting. Our tools offer a stronger design that provides greater capabilities and more extensive features. You are buying more tool. You are buying the capability, configurability, agility, and support system to best accomplish your work and to make you productive.

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