dave-in-nj:
you have a mechanical problem. a belt is held in place by the strength of the stepper.
in mechanics, you trade speed for strength. use a belt and one revolution = pi*dia of the drive pulley.
very fast, but the torque is based on the drive pulley diameter. so, not much holding power.
bumping the stop, will result in pulley movement.not may, but will.
using a leadscrew, you have one revolution of the stepper per thread pitch. on a large dia, say, 1 inch, and 4 TPI, you have to rotate a LOT to move 8 meters. 8 meters ? wow, that is a large table.
I would offer that a physical stop may not be the best means to control distance. run your belt, but move a sensor to detect the part. have two, or more, detect when the part is close, then slow the feed and stop when it is at your distance.
that way you have a non-contact sensor.
as for accuracy, you can get sloppy and maintain 1 mm.
taking a stab at the project, a 2GT pulley with 6m bore means you are going to run about 30 teeth on the pulley.
you may want 8 or even 10 mm bore.
a 30 tooth pulley will be about 28mm dia, or pi * d = 87 mm circumference.
a stepper with 200 steps per rotation will move the belt in 0.43 mm per step or 0.22 mm per half step or 0.11 mm per quarter step with a quarter step being a very good balance between strength and speed.
not sure how you would write your sketch to ignore 10 steps.....
probably better to just let it be accurate to 0.1mm and not try to make it sloppy.
Hey, thanks a lot for Your post. Leadscrew is out of the picture cause of the price. Here it's almost impossible task to go leadscrew even in short distances cause of the prices, and I have whole 8 meters to cover...
I went with 20 teeth pulleys as to keep power lower and easier to maintain precision. As I plan to keep prototype small - later I can adjust as needed and buy larger pulleys.
I think depending on a stepper lock down could be a problem, and that is why I decided I would go -> input position -> stop plate positioning it self -> automatic system turn off -> manual lock down in place.
I know manual locking kind of puts the whole thing useless, as I could then also position manually with a tape measure stuck on table, but I cannot find a solution that would fit. Was thinking of small servo motor on a stop device that would lock after positioning, but then I should have 8m wires going back and forth, which I am trying to avoid...
Non-contact sensor is not possible, as I unroll very thin metal stripe until the stop, and cut it manually. We unwind it it from a roll manually till length stop, and then we cut it to measure. If the system to unwind the coil would me motorised, than I would go the way You described, but that's a project for a future 
But I do think something about slowing down the speed before reaching the input distance, think this is the must to eliminate the overthrow as much as possible.
dave-in-nj:
if you only change a few times a day, you could move your stop and then lock it in place. that would be easier than trying to use the belt to do that.
I chose 30 tooth as below that you have a smaller bore. 8 meters will require a LOT of belt tension to prevent a belly.
you can use a large bright LED type letters to display distance. huge, letters if you like.
as for resources, you do not need a lot of resources in the Arduino. an UNO would be fine.
you move, let the unit do that task. you stop, maybe make a few correction steps
lock the belt in place.
then display the distance.
since you are not trying to do a lot at the same time and in a short period, you can do each step, then move to the next, in less than a second.
Thanks, I am considering to manually lock the stop piece when it's positioned, to program a automatic system shutdown when it's positioned, and then lock it with lever or something.
I am aware of the tension issue and that I should go with bigger pullies, but I kind of decided to take the less teeth pulley to keep the power request lower and precision higher. I can always get pulleys redone locally if needed.
Regarding LED, You mean matrix?
