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Looong thread about lathe macros here
forum.linuxcnc.org/41-guis/26550-lathe-macros

Are the encoder outputs differential or single ended?
If differential, i would use one output for whatever it is being used now and the other to Mesa 7i95T.
Be aware that everything connected that way must have the same 0/gnd/be on the same potential.
I have one such system in use for exactly two years!

nigelh wrote:

However being a bit of an electronic engineer (retired industrial physicist) I worry about loads and impedences.
The 7i95t manual section on the high speed encoders ofers me:
   DIFFERENTIAL MODE IMPEDANCE the min=118 max=122 Ohms
and I'm perplexed. I suspect I am thinking of something different.

Have you ever tried to explain to an inexperienced electronic guy, how the old antena cable (RG58) was 75 Ohm, and the security camera cable (RG59) was/is 50 Ohm?
I've gotten some very strange looks when i tried that... It all seems like black magic to them, till they dig deeper into the subject.

A scope is cheaper than any Mesa card, the MiniWare DSO211 is ~40$ and 212 is ~60$ for two channels.
To "safely" use the Mesa field inputs, 7i84 set in Mode 2 should have 4 analog inputs (00-03) at low resolution and low speed, add a resistor to each input. Probably will not be enough for what you need.
Using FPGA inputs as logic analyzer with some resistors is OK, but care must be practiced as those inputs are very sensitive, and adding zener diodes to each input is advisable. These inputs are fast enough for most uses, are 5V tolerant but with 0-3.3V range.
Any of those will not be very usable for finding interference as all above are DC coupled, whereas you would need AC coupling to measure interference.
And to make things worse, interference from cheap switching power supplies and motor drives and VFD's can in some cases be over 60VPP (volts peak to peak), meaning it can easily destroy any of the above setups.

It is only A and B for counting. You should probably verify with an oscilloscope that the signals from the encoder look like a nice quadrature signal.

RotarySMP wrote:

If you install Andy's "Lathe Macros", you get a set of canned cycles to do all the typical lathe ops, including threading with simple conversational interface. I beleive it works on most of the GUI's.
github.com/andypugh/LatheMacros

I of course use Gmoccapy as I like it modal nature.

 I will definitely check this out. I don't suppose there is a demonstration video? 
I'm trying to visualize this, especially WRT the axis GUI ( perhaps that's the problem?), and if I need physical buttons how many?
 If Axis is not the way to go then need to think about touchy vs. Gmocapy.

My hardware can't get here fast enough.

Move it to plasma section or to show your stuff?

If you install Andy's "Lathe Macros", you get a set of canned cycles to do all the typical lathe ops, including threading with simple conversational interface. I beleive it works on most of the GUI's.
github.com/andypugh/LatheMacros

I of course use Gmoccapy as I like it modal nature.