Threading with A B phase only?

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25 Sep 2016 12:32 #80900 by Mtndrew77
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.

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25 Sep 2016 21:05 #80913 by PCW
Replied by PCW on topic Threading with A B phase only?
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)
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25 Sep 2016 22:22 #80915 by Mtndrew77
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

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26 Sep 2016 01:12 #80916 by Todd Zuercher
or you could simply add an index sensor somewhere. (are you sure that the machine might not already have one?)

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26 Sep 2016 03:17 #80917 by Mtndrew77
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

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26 Sep 2016 12:54 #80931 by Todd Zuercher
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.
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26 Sep 2016 14:25 #80932 by Mtndrew77
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

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26 Sep 2016 18:36 #80944 by Mtndrew77
Could my 7i76E handle a 24V signal on the spindle encoder interface? With 5v signals on A,B and 24v on index?

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26 Sep 2016 18:48 #80945 by PCW
Replied by PCW on topic Threading with A B phase only?
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
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27 Sep 2016 13:00 - 27 Sep 2016 13:00 #80993 by andypugh

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


What type of proximity sensor is it? A 24V 3-wire NPN Prox can be connected directly to 5V logic (they act as a switch to GND, rather than a voltage output)
Last edit: 27 Sep 2016 13:00 by andypugh. Reason: Added "3-wire" to be more specific

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