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Build a Tachometer
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| You can easily build a hand-held tachometer for your 7x** or Taig lathe. |
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What you'll need is
• a digital volt meter or multi meter,
• a Radio Shack PM motor,
• a 5K or 10K potentiometer,
• a plastic tube to house the motor and pot, and
• a small wheel with an O-ring "tire".
The photo shows the the finished tachometer.
Before you use the tach, you must calibrate to a known speed. The drawings show two methods: one for the 7x**, the other for the Taig.
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For the 7x**
The logical surface to read the spindle RPM's us the spindle flange.
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To get a known spindle speed on the 7x**, strobe the 45 tooth gear on the left spindle end under a flourescent lamp. (Adjust the speed control until the gear appears to stand still.) This speed will be 160 RPM (assuming 60Hz AC as found throughout the US). |
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Next, set your meter to read DC volts in the range of about 2V. Then hold the O-ring against the spindle flange and adjust the potentiometer until the meter reads 160.
The unit is now calibrated to read the RPM of the 7x** spindle flange. |
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For the Taig
The pulleys are matched (the are the same size) so you can calibrate to the motor speed from the nameplate data.
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Set your meter to read DC volts in the range of about 2V. Then hold the O-ring against the largest diameter of motor pulley and adjust the potentiometer until the meter reads 1725 (or whatever the RPM of the motor on your Taig is).
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| The unit is now calibrated to read the RPM of largest diameter lathe pulley. |
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| Richard 2004 |
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