CNC Spindle Encoder

Well, I finally got around to connecting up the steppers on my lathe. The next obvious thing to do was to add a spindle encoder so that I can do threading.

Spindle Encoder

The spindle encoder looks pretty boring in the box. The two whitish circles are pieces of plexiglass that I turned so I could see the LEDs inside. If I had thought about it a bit more, I would have had the LEDs poking out the top. The aluminum spindle reflects infrared really well, and a piece of black electrical absorbs the infrared acting as an interruption. Bigger...

Cover Off

Here you can see how the sensor is mounted, and you can see the insides of the encoder. I made the mount from a piece of sheet aluminum and cut it freehand using my metal bandsaw. Bigger...

Closeup

Closeup shot for people who want all of the gory details. Bigger...

Schematic

This is the schematic for the encoder. I created it using a rather nifty little program called TinyCAD which is a free schematic capture program. The O, G, W, and B letters next to the QRB1134 correspond to the wire colors which come attached to the sensor.

This is the TinyCAD schematic file: CNC-Spindle-Encoder.dsn, along with the custom part QRB1134.mdb which is for the QRB1134 sensor. Bigger...

Sensor Closeup

This is a closeup shot of the sensor. The E side corresponds to the emitter and is basically an infrared LED. The S side corresponds to the sensor and is a phototransistor. Optimal distance is about 0.150" from the sensor to the refletive surface.

I bought mine from The Mark III Store but you can also get them from Digi-Key or Mouser. Bigger...

Circuit Board

The circuit board out of the box. I used a 4 pin connector so I could disconnect it. The 74LS14 was from my junk box. I left the leads a little long from the sensor so I could adjust it, if required. Bigger...

Back Side

The back side of the circuit board. Just some cut up protoboard. Bigger...

First Part

This is my first threaded part using the CNC threading capability from Turbo-CNC. This piece is cut from a 1/4" steel rod (CRS - not leaded). The thread is 4mm x 0.7mm (cut using my imperial lathe - which doesn't really matter with CNC).

I created the G-Code for the basic outline using CAD2Lathe and added the threading passes by hand. Unfortunately, CAD2Lathe doesn't seem to be sold anymore.

The gouge out of my live center was caused by me crashing the lathe :( I entered the position of the toolbit using the diameter rather than the radius and the computer happily tried to drive the toolbit somewhere on the other side of the live center - whoops. It also chipped the end of the carbide toolbit. Good thing I had a spare.

I'm thinking that I should setup Turbo-CNC to use diameter mode. Firstly, when you measure anything on the lathe you always measure the diameter. Secondly if you screw up and enter the radius as the position, the worst thing that happens is that you don't cut anything at all rather than crashing. Bigger...

Here's Mark Wrathall's spindle encoder, which uses a slightly different design.

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Copyright 2006 by Dave Hylands