Layer Shifting on DIY Printer Mainly Dual Extrusion-Marlin-Rumba

Hi, I am sending myself crazy trying to find the issue that is causing my prints to shift after a couple of hours.
It happens every time when dual extruding the design in the image.
If I scale it down to half the size (and time) it prints okay.
I have had it happen on another single colour large print but not consistently like this dual extrusion print.
It is at different layers and in different directions each time.

Cartesian scratch built printer with dual bowden extruders.
Latest Marlin on a rumba board.
I have done the following.
All belts and pulleys are tight.
Swap all a4988 drivers
Check drivers with temp gun and none are hot
Swap Rumba board for another.

My next thought is to rewire but that is a major headache.

Is the x stepper motor driver overheating? Try a fan or lowering the current if it's overheating. If you can't keep your finger on the chip or heatsink, it's too hot (temperature higher than 60 degrees C). A temp gun readout area could be too large, misreading the temperature on those tiny chips.

Is the current too low? Try increasing the motor current.

Also check if it skips steps at the highest velocity/acceleration the firmware allows.

With gcode like this:
G28 ; Home all axes
G1 Z10 F900 ; Move Z away from hot end
G1 X50 F18000
G1 X150 F18000
G1 X50 F18000
G1 X150 F18000
G1 X50 F18000
G1 X150 F18000
G1 X50 F18000
G1 X150 F18000

Is it making a lot of noise when changing direction? Try lowering the acceleration.

Edited 1 time(s). Last edit at 01/25/2019 08:46AM by imqqmi.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

Okay, thank you for your advice.
I will try the gcode today.
The heat sink is not even warm to touch.
I am thinking of taking the heat sink off so I can check the chip itself.
Cheers

They are really large layer shifts.

The only time I've had layer shifts anywhere near that magnitude was when I was printing while the washing machine was running. Every time the motor switches off the field collapses & the counter EMF puts a spike back through the houses' wiring and causes the steppers do all sorts of crazy stuff. Anything that switches an inductive load (like a motor) on and off can turn a clean sine wave supply into a dirty mess.

It may not be what's causing your problems but it's something to consider if you don't find any other problems.

Good points, I have wondered about the effects of other equipment as I notice fluctuations when my water pump starts etc.

It looks as though imqqmi has picked it though.
My acceleration was very slightly too high on the Y axis.
I am having other problems now so still can’t be absolutely sure but will keep trying.
I would definitely recommend to anyone building a scratch built printer to run a gcode as imqqmi suggested for all axis.
I had never thought to test the limits of speed and acceleration of my printer.
Now I know it’s limits I have tuned it. One less thing to worry about.