Just completed a large version of the i3 so I have a build area of 250 * 350 *350 high. Moved all the gear from my old i3 and all working except that it randomly looses steps on x always in the one direction.
Replaced the cable, smooth movement, nothing binding , so over the last 5 days ( about 30 dry runs) , changed the stepper drive current from just enough to move till it was nearly going into thermal shutdown, same result
I did see it do it once as there was no sound from the printer and when I look up the X had stopped for about 2 seconds and when it started moving again was clearly now in the wrong place as it should have been moving right at that time and was now 2cm too far left.
I am about to swap the X/Y direction to see if the problem moves to Y or stays with X but any other suggestions and what this could be and it’s not a loose belt.
Are you having more of sliding layers of is it that you can hear the skips step? If it’s just sliding you might want to check that your pulley isn’t slipping on the motor shaft or the belt isn’t slipping.
@Griffin_Paquette The belts/pulley are not slipping as I have marked the positions to ensure that. Not sure what you mean by hear skipping steps, I saw it do it once and there was silence when it should have moved right
When a motor skips a step you usually hear a knocking sound. Its hard to describe. What type of control board are you using?
@Griffin_Paquette , thanks, good to know about the knocking so I had none of that, it was like the command never arrived to move, silence. This is ramps 1.4 board and this was all just lifted from the old machine and fitted to the new and that’s the frustration. I am using a different USB cable as the board is in a diffenett place but I would not expect that to be the problem as I would get the misses moves in random directions but I will try that anyway 
I would say that you should switch the stepper driver with one from another axis, that way if that axis starts having the problem you know that it is the driver. Honestly I would just replace the ramps shield. They are crazy cheap on eBay. I am on my third as the first had problems with the z-min port and the second kept giving me mintemp errors. I finally bought a Sainsmart shield (actually got it at my local Microcenter and they price matched Sainsmart’s online price). The new board seems fine. The RAMPS are not the most reliable in my opinion.
@Griffin_Paquette I had switched the driver and did not help, I will try the USB cable next ( not expected to help) and then the X/Y axis to see if the problem shifts, takes about 1 hour each run to get a large shift.
So is it happening a ways into the print?
@Griffin_Paquette It’s Random times, I just know if I leave it run for 1 hour I get an easy visible shift, I am in dry run mode and move to specific locating i have marked on the bed when I pause and move to that place and see if it still lines up
Completed the X/Y swap and the problem moved to Y so something on the Ramps is the problem.
Wait so was it on the X before’?
@Griffin_Paquette Yes, Only X and only one direction, with the swap of the X/Y now it’s only Y and only one direction
So did you switch the stepper drivers or just switch the stepper plugins?
@Griffin_Paquette With just the drivers, the problem was still with X, then swapping the plugs and end stops it moved to the Y
So if you moved the drivers and the issue changed axis’ then you have a bad driver.
@Griffin_Paquette Moving just the drivers and nothing changed, it was still the X, but yes there is an issue in the X control side but not the driver
Ahh so I would definitely change out the RAMPS shield then. They are cheap on eBay but I would recommend getting a good quality one. It will be less of a headsche
@Griffin_Paquette I am looking for a local supplier now
Good luck. The only one I’ve found is Microcenter.
@Griffin_Paquette I do not think they are in Australia