CNC Spindle Motor Load Meter – ammeter
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Hi everyone. This is a short video of making a poor man’s
spindle load meter using an ammeter and voltmeter. A subsequent video will use power meters. The voltmeter is attached in parallel and
the ammeter is attached in series. Since these are unshielded meters, care should be taken
to dress the ammeter wires following the meter’s instructions. While this load measurement is qualitative
because of nonlinearity between current and motor power, the estimate is still useful. For a 1HP brushless DC motor supplied with
120 volt and assuming optimistic efficiency, the expected current draw of the spindle motor
at full load is roughly 6.25 amps. Here a 3 inch aluminum part is being faced
with a fly cutter, 50 thou depth of cut, 2500 RPM, with a feed rate of 10 inches per minute.
The current meter suggests we are near full load. Most operations that I do, barely budge
the needle. However, while drilling with a 1/2″ drill
bit the meter jumped to 15A. I didn’t notice the indicated speed but the spindle motor
sounds to be struggling. I hit the e-stop and reduced the feed-rate. Without the power meter,
I would have kept going, potentially doing damage. The g-code to cut the front panel was prepared
in Fusion360. A summary of tools and operations can be generated
by Fusion360, and this is a great place to write additional notes, including performance
observations. The stock material is 1/4″ plywood, cut to
size on a table saw and held to a sacrificial piece of MDF with double sided tape. First,
screw holes are drilled, and a few will be used to help hold the stock in place. The last operation is 2D pocketing, with multiple
depths of cuts, with a 1/2″ end mill to cut holes for the meters. Given the cost of quality
hole saws, having a CNC mill to cut panel holes is nice. With light sanding, the part cleaned up nicely.
The side facing the MDF was pretty clean. A vacuum attachment might be nice. Thanks for watching.

2 thoughts on “CNC Spindle Motor Load Meter – ammeter

  1. Thanks for your videos Kent!

    Hints for others (I'm sure you know this) use your 'esc' key to stop the program (not your e-stop) unless it truly is an emergency, this way you save your homing. Also, you can on the fly change your feed rate using the numbers on the keyboard: '8' on the keyboard will change the current feedrate to %80 of the requested value.

    Thanks again Kent, I'm going through your older videos now.

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