$250; Pushing The Limit On Cheap (And Functional) CNC Machine Builds


$250 cnc machine - rotary tool

Cost is always a drawback and a hurdle when buying or building a CNC Machine, especially when building it just for fun or hobby. [Eric] was able to cobble together a working 3-axis rotary tool based machine for about $250, a few trips to the hardware store and a bunch of time.

The machine design is loosely based on this one he found on Instructables. [Eric] chose this style because he felt the boom supported tool would have been more stable and easier to build than a gantry style machine. Skate bearings, HDPE sliders and c-channel aluminum were used to support the XY table instead of traditional linear bearings and rails. All three axes are driven with stepper motors and 1/4″-20 threaded rods. The Harbor Freight dremel-style rotary tool helps keep the overall cost down.

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Adding an RPM Readout for a Home Made CNC Mill


[Rui] recently put the finishing touches on his homemade CNC mill, which utilizes a dremel-like rotary tool. The problem with using rotary tools for this kind of application is you don’t really have an accurate speed readout… so he designed his own RPM gauge.

The sensor is in itself very simple. He’s using a TLE4935L hall effect sensor, a spare 16FE88 microcontroller, a Nokia LCD, and one tiny neodymium magnet. The magnet has been carefully epoxied onto the motor fan, with the hall effect sensor close by. He’s also built a guard around it, just in case the magnet decides to fly off at high speeds.

During testing he hooked up the hall effect sensor to both his home-made circuit, and an oscilloscope to confirm his findings. Once he was assured everything was working properly he sealed it off and mounted the LCD above the spindle as a nice digital readout.

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