What is the advantage of using a motion controller rather than just a PC and BOB?

[Agathon]

Fwiw..
If You are working on a fehlmann..
which is a high-value machine - top of the range -
I would definitely recommend ac brushless servos and a csmio controller.

A motion controller provides much smoother pulses, and at much higher step rates, than other options.
But..
All the high-speed stuff is then dependent on the motion controller, and thus their sw/fw/plugin support is critical.
This applies to high accuracy servos, high accuracy homing, high accuracy probing, etc.

Servos, modern, have 5-10k counts/rev.
Thus, at 50 r/sec, = 3000 rpm, = 500 kHz.
Very few systems support this.

A csmio basic does 256 khz.
It might be fine.
And supports 4 axis.

But..
I think it does not support rigid tapping as-is.
Not sure, check with cslabs.
If this rigid/tapping does not matter, that would be Your best solution, today, imo, ime.

If You want a Really Good solution, get a CSMIO-IP-S or IP-A.
I use IP-S on a lathe, industrial, servos, very happy.

If You want a Really Good solution cheap, get a Pokeys Ethernet board.
Low cost, excellent sw, support, hw.
Limited to 125 kHz, mostly wont matter imo, ime, for the speed.
Mach = 125 kHz but I think Mach4 is higher speed.
6 axis.
And *excellent* MPG support.

I would recommend against anything else, especially usb, exception machmotion and other industrial stuff, I have never heard anything negative about.
So those c/would likely also work really well- no personal experience.
A smart read is that I am not mentioning some popular hobby controllers - some that I have. There Is a Reason.

Thanks for the reply. I think I'm going to heading along the LCNC route (I'm going to give it a go at least). I've been put off up to know by the lack of a clear guide that assumes no experience of CNC (like the very good Mach3 manuals), but a number of people including Clive S have encouraged me to persist and give it a go.

I recently mistakenly bought some analogue servo drivers (very cheaply) which I'm really impressed with after powering them up and running them from the manufacturers control software. Given how easy and relatively inexpensive it is to buy a Pico Systems DA converter card that will run straight off LCNC it makes sense to give that pathway a go. So to some extent the motion controller issue isn't so important to me now.