How to design and build a CNC router
Why shell out big bucks for a CNC router when you can build a DIY CNC machine from scratch? This article explains the steps involved in building a homemade CNC router.
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Things You'll Need
- Router head or spindle
- A sturdy machine base frame
- Linear guidance rails
- Linear drive system
- Servos or stepper motors
- CNC control system
Instructions
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Start by deciding what material you want to cut and what type of router or spindle you'll need to cut it. While this may seem like it should be the last step, it is important to start with the cutting head and build the machine outward from there.
While a common plunge router is the obvious choice, be aware that the cheaper models will probably not hold up well under continuous CNC cutting for hours. For metals such as aluminum, a Minimill or Micromill milling machine head can be adapted to your machine. You can also build your own spindle using a collet chuck and some ball bearings.
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Determine the machine's travel and work envelope. Start with the width under the gantry. If your raw material is 4'x8' sheets of plywood, for instance, you'd want the gantry to be at least four feet wide. Even if the travel in the other direction is less than eight feet, you can still gain access to cut parts from the entire piece by unclamping it and sliding it over.
While the material you are cutting may be quite thin, be generous with providing z-axis travel in order to accommodate different router bit tool lengths.
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Design the base and table. This is the foundation of your machine and the accuracy of the rest of the router will be determined by how rigid, straight and flat the base is.
Aluminum extrusions such as t-slotted 80/20 rails are a popular choice. The base can also be welded from steel but watch out for distortion. On a smaller, less critical machine wood or MDF board can even be used.
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Obtain the linear guidance rails for the motion axes of your machine. Rectangular profile rail guides are often used. Round rails and open style ball bushings can be used if the rails are fully supported along their length by t-shaped mounting rails. On a very small machine, round rails can be supported only from their ends but don't underestimate the lesser rigidity of this configuration.
Precision linear motion components such as these can be expensive to obtain new, so consider searching eBay or surplus sites. Sometimes you may need to adapt your machine's size to match the components that you are able to obtain.
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Select the linear drive system. Ball screws or preloaded nut ACME screws will work for smaller machines and short travels such as the z-axis, but long screws will experience problems with whirling and buckling.
For a large machine, rack & pinion, cog belts or fine-pitch chain are better choices. Consider driving a wide gantry from both sides to prevent racking and binding.
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Select your motor drive type and coupling system. Stepper motors are a low-cost open loop option but may experience problems with lost steps. DC servo motors can make for a very fast and powerful machine but have the added cost of optical encoders for feedback.
While stepper motors can often be coupled directly to the drive system, servo motors usually require a gear reduction such as a cog belt and a pair of pulleys.
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Finally, now that you have the mechanics of the machine designed, you'll need a CNC motion control system to run your motors. See my article on building a home CNC motion control system.
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Tips & Warnings
CNC machines can be powerful and move quickly - Use caution. Take appropriate steps to guard the machine and always include an Emergency Stop switch.
