Hi all,

I have been battling seemingly "random" layer shifts on my delta printer for a while. The shifts are not major, 0.5mm-ish here and there, just enough to ruin the print.

I have done all possible steps to eliminate as much as I can:
1. print from SD card.
2. drive motors with full rated current (1.6A), putting lots of extra heatsink on top/bottom of the board with thermal tape, and cool them with fans.
3. reduce acceleration/jerk to half the default setting (no effect)
4. reduce print speeds to 1/2 the default speeds in simplify3D (no effect)
5. capacitor banks at the output of power supply and input on smoothieboard

As of last night during a filament change, I noticed this:
I unplugged the extruder stepper motor by accident, then in pronterface I set the printer to extrude 100mm——all 3 (x y z) stepper motor engaged, and I can hear distinctive clicking, I can physically feel the clicking too, I am not sure which motor is clicking, but there is no visible movement anywhere.

Then in my mind I realized that the layer shifts only seem to happen when the extruder motor struggles to push the filament through (due to over extrusion, filament diameter bigger than what is expected). When the extruder motor struggles, I can hear loud clicks, and I can see the gear that pinches and pushes the filament physically skips—-sometimes dramatically.

When I set simplify3D to physically under-extrude (done it multiple times), I can confirm 100% that the extruder motor never skips and the layer shift never happens.

In pronterface, @version returns the following if it will help in anyway:
@version
SENDING:version
Build version: upstreamedge-b6153da, Build date: Jun 21 2017 21:02:36, MCU: LPC1769, System Clock: 120MHz
5 axis

Can someone shine some light on this? Am I barking up the wrong tree? What is happening here? What other measures I can take to avoid layer shifts?
Any comments, recommendations etc will be greatly appreciated.

Kind regards,

Gordon