CNC conversion Questions and Linuxcnc

I'm planning conversions for a g0602 lathe and a PM727 mill both using Linuxcnc. Looking at boards from cnc4pc. Arturo says the c3 boards are only good for 20k, so will be ok for the lathe under 2000rpm, but probably not for the mill. How many pulses per revolution does one need from encoders for linuxcnc? how does linuxcnc deal with different gear or pully ratios on spindle drive? I understand that encoder feedback is necessary for lathe to do threading and constant surface speed, but is there any advantage to spindle encoder feedback on a mill? Planning on Leeson metric 3ph motors for both conversions, 1800rpm motor on lathe and 3400rpm motor on mill. Some say rs484 best for comm between vfd, any thoughts on this? Would Mesa boards be better choice? And if so why and in what ways?...or is it just a matter of personal preference and price?

Did I post these questions in the wrong category? If so I apologize...and please advise if there's a more appropriate category to post. Looked through a lot of previous posts for answers but not much luck. Was hoping others with more experience could give me some direction

The main advantage I can think of for having encoder feedback on a mill would be doing rigid tapping or gear hobbing. I'm not sure what else you might need it for.

Rs485 is a way to add a lot of spindle control features without doing a lot of wiring. The down side is I may not have the greatest real time performance.

Mesa cards are great hardware and usually well worth the added expence.

Todd wrote:

Mesa cards are great hardware and usually well worth the added expence.

X 2, I've just tuned my Z axis using a 7i76e and I'm getting about 90k steps per second and the little Nema 23 is fairly screaming.

Thanks for the replies. Looking at the Mesa 7i76 and 7i76e, the max encoder input is 10m compared to only 20k for the cnc4pc. So, Is the 5i25 card a sort of high speed proprietary parallel port? Does the ethernet version provide any better performance than the PCI/PCIE versions? Ethernet would be more work to set up tho I'm guessing.

I think the ethernet one might be a bit slower but its immaterial becasue the limiting factor is the step lengths and other step timing issues your stepper controller can accept. I got a few warnings from LCNC today when I really pushed the limits and I got a bit more velocity out of it by reducing these timing issues in my .ini file.

Its your choice which way to go. I went with ethernet because I'm building a plasma machine and I wanted to physically keep the PC away from any electrical noise. Others prefer to use the PCI/PCIe way and treat the PC motherboard as another component in their control box.

I suppose it depends on a lot of variables such as drives, motors, machine size etc as to whether or not these cards will provide faster cutting speeds? ...sounds like faster rapids likely in most cases tho.
Can either hall effects or optical encoders be used with 7i76, or does it have to be optical? Is there a range of pulses/rev that work best with 7i76 and Lcnc? Not finding any schematics as far as hookups or block diagrams in manual...is there a schmit trigger on 7i76 board or does one have to provide one on sensor or in between to clean up signal?

The 7I76 encoder input has a small amount of hysteresis,
In addition, all encoder inputs have programmable digital filters

Are the input filters programmed through firmware, or can this done through linux? Didn't notice any mention of this in Mesa's manual, is there some other documentation I missed somewhere?