How to build a CNC Router?

No Mesa 7i92 for you!
Get the Mesa 7i96S, it is much easier to wire in and less sensitive to mishaps.
For now, old PC parallel port, some cheap drives, get the machine moving.
Or get the Mesa 7i96S and some cheap drives and make the machine move.

Haha, post lost, so I re-invent it.
I think for basic experiments a 10 USD parallel port PCIe card and a bottom level parallel port break out board wiill get you up and running for 20USD. (excluding wasted work and life time).IO
The MESA card solved my encoder issues within short time and I (#not sponsored) th think it was a good decision, even if someone informed me that I could have bougtht a "yet again undocumented" device for 5% of the MESA  fee,


 

OK, so
Mesa 7i96s it is (should be worth it, since I can us that one for the big machine later)
3 of the TB6600
Leaves the PSU question. I think I have an old ATX PSU. Those deliver 2-4 lines of 12V and several 5V lines. Could that do for the small steppers?
And my Thinkpad x220.

Yes,
yes,
yes,
...
no!

ATX PSU is OK for testing and running the machine, but will limit the speed.
X220 is the "no" up there, had 2 of those, absolutely not usable for LinuxCNC, but since you have it, get the ISO, burn to USB, boot the X220 from it and do some latency tests as follows
latency-histogram --nobase --sbinsize 1000 --show
Also had 2 of X240 (still have one) both were/are fine for running LinuxCNC.
If the latency turns bad, i can upload an image i use on all my production laptops and PC's with Mint 19.3 and LinuxCNC 2.8.4, but this needs to be installed to be able to test it.

Will do the tests later, here is what I have available:
TP x200 tablet (the one which turns the screen 180°
TP T43
TP T420s
ThinkCentre M625q

One other thought was perhaps to get one of those used Getac outdoor Notebooks (but that was mainly because of the dust and water protection features)

OK, T43 is i686
screenshot from latency attached for the 2 others.
I did run glxgears and a youtube video. The max. µs Value was half until I resized the glxgears window.

Well there is my favored refurbished dealer, offering T470 with touchscreen and 8GB RAM for 137,- EUR right now. might be the best idea..