Monday, October 27, 2014

Lathe: Arduino TouchDRO

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After finding myself with an extra iGaging digital scale I decided to convert to the lathe to use the Arduino and Android powered TouchDRO. I had already installed an iGaging scale on the Z axis (see previous blog post) and adapted a cheap Chinese caliper to the cross slide. Going to an Arduino powered TouchDRO meant replacing the caliper with the iGaging scale.

The scale's read head needed 1.5mm machined off the cover's mating surface. A new bracket holding the scale needed to be made as well. While I was at it I added a second mounting screw for the read head to insure it won't wiggle on a direction reverse as the scale's guide wear.

New iGaging scale mounted to cross slide.

 Unlike the mill's Arduino, I constructed this one using a prototype board. It's much cleaner and easier and I highly recommend it, even though it added $8 to the build. I used standard USB A connectors for the scales' interface since both connectors and cables are much easier to find. This forced me to change the cables on both scales, but that didn't cost much. The tachometer's plug is also USB to avoid the issue I had using a 3.5mm headphone jack for the tach on the mill. Everything was mounted in an old Dell laptop power supply brick's case I had on hand. Neodymium magnets were glued to the case's top for mounting on the back of the lathe.

The tach, like the mill's, uses a Hall effect sensor since they're much easier to set up than an optical sensor and are just as accurate in this application. The lathe previously had a spindle extension installed, and for the tach's magnet I drilled a hole on the extension and used JB Weld to mount a small neodymium magnet in it. 

Spindle extension with magnet mounted.

The tach's sensor was mounted to the outside of the lathe's gear cover. I considered mounting on the inside but space would have been an issue and it works perfectly well on the outside. I covered the top of the sensor with epoxy putty to protect it and keep any swarf from shorting it out. If you look closely you can see I've bent the sensor itself up and away from the spindle; that's to provide a more optimal orientation to the magnet. The sensor's USB cable is run down the back of the lathe to the Arduino's case.

Hall effect sensor mounted on gear cover.

I'm using a HTC Incredible 2 phone as the Android device running the TouchDRO application. Since the lathe only has three readouts (X,Z, and tach) the phone is adequate. It's currently mounted to the top of the headstock using a bracket I fabricated. 

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