I'm making good progress on my 3D printed CNC conversion. I found a way to 3D print a spindle controller that should work for most small milling machines and small lathes. The cost is "almost nothing". These machines' spindles are controlled by turning a potentiometer so my new system simply uses a cheap model airplane servo to turn the shaft of a potentiometer. The computer is 100% isolated from any high voltage or noise.
These small mills will never be able to do things like rigid tapping so all they need is a simple and approximate way to control the RPM. This speed control can be run "open loop" if plus/minus 20% is good enough or used with a spindle encoder in a closed PID loop as long as the PID is tunned not to aggressively. For anyone who does not know about these hobby servos: - They are not full rotation motors. They turn only through about 250 degrees, This is a good match to the pot as pots also rotate about this range. - The angle of the servo shaft is controlled by a PWM signal. - They are "dirt cheap" starting at about $5 amazon.com/4-Pack-MG996R <https://www.amazon.com/4-Pack-MG996R-Torque-Digital-Helicopter/dp/B07MFK266B/ref=sr_1_2?dchild=1&keywords=mg+servo&qid=1592502600&sr=8-2> - They accept a 5-volt control signal, so they have a built-in computer interface. - They are fast (enough) and can move from full-low to full-high on 0.6 seconds - They really are actual "servos" and have an encoder, motor driver, and gears all inside. So when LinuxCNC outputs a low-value PWM spindle control, the servo moves the pot to the low position. As the PWM signal value gets larger the pot is moved closer to the high-speed position. In the picture below is a cartoonish render. The green frame is one-piece 3D printed, The red pannel and tan coupler are also 3D printed. The motor sells on Amazon, four units for $20 and the pot is about a buck each. Four M4 button head screws everything together. Here is a link to the current version CAD files and a viewer. I'll be updating the files after the first prototype is printed. https://a360.co/2N95AiL I may make a top cover to protect the pot and keep fingers off the high voltage. [image: Red Neck Spindle Control v6.jpg] -- Chris Albertson Redondo Beach, California
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