Lathe conversion spindle encoder question

I got my hands on a 65 year old myford lathe and I'm in the process of brainstorming the cnc convertion for it to be used with Linuxcnc. I will be replacing both the cross-slide and carriage leadscrews since they are worn in an un-even way and probably impossible to accurately compensate for backlash. any suggestions are more than welcome.

now my question is here: I intend to mount an encoder plate to the spindle which will give a quadrature output and an index pulse (sort of this members.shaw.ca/swstuff/spindle-encoder.html), how can I determine the maximum frequency that my system can handle according to my BASE_PERIOD? (I need this info to determine the amount of PPR the enocder will produce). In the documentation I only found:

Maximum speed in thread
The maximum spindle speed used in threading. For a high spindle RPM or a spindle encoder with high resolution, a low
value of BASE_PERIOD is required.

Well a quadrature encoder needs to be sampled at least once every state (and there are 4 states per slot period). Also encoders are never perfect so will have some short and long
states due to slot imperfections, detector thresholds, etc. The base thread likewise will have some jitter. So if I use a safety factor of 2 to allow for these imperfections, that gives me:

MAX RPM = 60 / (BasePeriod* Slots *8)

Hi

This covers a similar query
www.linuxcnc.org/index.php/english/compo...=30&id=14682&limit=6

Regards the Myford, MEW (Model Engineers Workshop) ran a series on converting one to CNC some while back.
Might have some ideas, although I seem to recall some bits were a bit 'Heath-Robinson'

regards

Finally found the articles, not quite as 'Heath Robinson' as I recall, with the exception of the control and VDU mounting arrangement - you will see what I mean!!!

It was issues 138, 139 and 141 of MEW that had the articles of interest.

Thankfully they are all on-line on Tom Jeffree's website www.jeffree.co.uk/modelengineering.html

regards

thanks PCW that formula was exactly what I was looking for.

thanks also to ArcEye, I looked into those already however my design will be different since I will be replacing the leadscrews and nuts with new ones (not myford original) probably from worldofcnc.com aka marchantdice on eBay. also his solution for spindle position tracking is a hall effect sensor with one pulse per rev, he mentions that mach3 estimates the current spindle position by taking into account the rpm and the index pulse but I don't think that should be the way to go....

still, the way he mounted the motors especially for the cross slide is clever. they gave me some ideas, but I think I will probably couple the leadscrews directly to the motors and avoid belts & pulleys.

that is pretty neat,

however this lathe was my grandfather's and my father wouldn't like me messing with it since it has a sentimental value. So I'm restrained by that, I want to be able to remove the conversion and install back the machine to its original state. I was thinking something like this for the cross slide, it uses a 10mm diameter 2mm pitch leadscrew and bronze/delrin nut (probably bronze)



for the carriage I will probably be using 14mm diameter 3mm pitch, again with a bronze nut however im still wondering if I should directly drive the shaft or use a pulley, with a 120oz-in stepper