Problems of lock with Nema 23 Steppers

Check that you have a machine profile configured properly 533.x steps per mm as shown briefly in the video doesnt match our standard machine profiles, so I assume you edited the values? (Our leadscrew machines are 199.1 usually). When changing to such a higher a steps-per-mm value you also need to adjust your acceleration settings accordingly: Our included profiles are setup to work as-is, when modifying settings from default expect them to have impact on other settings too.

See gnea/grbl

If acceleration is too fast, the motor cannot overcome enertia and thus stalls

 

No that hardware is fine, but when you changed steps per mm, you should understand that other settings like acceleration,etc may also need changing to match your configuration that is different from the stock machine, and thus why the stock profile stalls. Just edit your settings, follow the link I included in the reply above for all the information. Grbl Wiki is a treasure trove of info, worth reading the whole wiki to properly understand Grbl

 

Those leadscrews are high accuracy, low speed, being only 3mm pitch. Our stock screws are 8 mm pitch, so keep that in mind, the low pitch on your screws will slow you down for sure. Spend some time tuning your Grbl parameters (may take a few hours to dial in maximums....) first, but do keep in mind those screws are not ideal for fast feedrates

3mm pitch, single start

Our screws are TR8*2 but 4 start, so each rotation is 2mm x 4 helixes = 8mm.

 

Correct, but you might get 12mm leadscrews in an 8mm pitch which is closer to the stock profiles. Picking a 3mm pitch is a done deal now, and that is a limitation because it needs more rotations to travel the same distance, and thus will limit maximum feedrate, for the same maximum RPM. Regardless, all I am saying is, expect to put in the work to develop a profile that plays nice with your changes

Well, very hard to say, but with the stock configs you can get up over 5000mm/min, so with no consideration for other factors (enertia of heavier screw, higher fricting in the bigger blocks, etc for which we cannot account) just looking at the pitch, 5000 /8 * 3 = 1875mm/min at least

Depends on the recipe though; single flute vs two flutes, depth of cut, endmill diameter. Did you account for flex in the machine frame (large format machine will have some flex, probably will be limiting your feedrate more on this than the speed the leadscrew can handle) etc.

 

Lets put it this way
There's good reasons we only stock prepacked kits up to 1000x1500mm. Beyond that there's just about too many compromises, so "upgrades" tend to make me feel worried already.
Belts over 2m will suffer stretch issues... So look at the Dual Belt system (hit the search at the top) to help with that, but yeah will be faster (with less accuracy, less torque) - so decide on your compromises.

I'd say keep the 12mm screws and forget what you read about feedrates. Build it, run it, adapt to what it does in the real world. 1800mm/min is plenty fast.