Threading with A B phase only?

I was just wondering if it was possible to thread with A B phase only. I was thinking it might be possible to generate the index signal based on encoder count. Has anyone done anything like this? I just found out my spindle encoder does not generate a index pulse and I'm trying to save myself from buying a new encoder.

Yes, It has been suggested to add this to the encoder component ( a synthetic index signal from raw encoder counts mod counts/turn) but its probably not a common enough need that the combination of someone capable of adding the feature and needing the feature exists.

Of course there are some compromises with this approach:

1. index is volatile (so you cannot restart threading or rigid tapping operations if you exit LinuxCNC for any reason)

2. You are more dependent on never losing any encoder counts (You _should_ never lose any but re-syncing to index is more robust)

I suspected as much, but figured it was worth asking. Creating the component is out of my realm of expertise so
I think I'll just shop for a new encoder.. Thanks

or you could simply add an index sensor somewhere. (are you sure that the machine might not already have one?)

Its a Emcomat 20E, and It had a 24V Omron prox switch for indexing before. The spindle encoder was a Rod 420 Heidenhain, and the index was intentionally grounded out. For the life of me I can't figure out why they designed it that way but they did.

I haven't ruled out using it, but if I can find an encoder at a reasonable price it just makes a cleaner install

Is the encoder connected to the spindle in a 1:1 ratio? If it isn't , then you need to use an external index anyway.

Well it is but I guess it may not be exact since it is running off an idler shaft in the headstock. Didn't think of that one, but it makes the most sense to me

Could my 7i76E handle a 24V signal on the spindle encoder interface? With 5v signals on A,B and 24v on index?

Not directly, but you can make a simple voltage divider with 2 resistors to get the signal down to a 5V level

24V index --> 1K Ohm 1W --> 250 Ohm 1/4w -->GND
the 5V signal is taken at the junction of the 1K and 250 Ohm resistors