Hi all.
Hope I'm posting this in the correct place. Newbie poster...
So - I've built myself a 5 axis mill and am banging my head against an electronic wall. This is my 3rd build and up till now have been running 3-axis with G540's / mach3 with zero glitches.
I know I shouldn't have skimped on the control gear, but hindsight being what it is... here I am.
I thought I'd throw this out as a last resort before trashing the whole box and going with 2x G540's in parallel with an SS-02 Ethernet smoothstepper.

Currently, the control box consists of:
Novusun NVUM V2 USB 6 axis controller (the suspected culprit)
6x TB6600 stepper drivers (one redundant)
5x 1.9Nm Nema 23 Stepper Motor 3A (microstepped @ 1/8)
Mach3 running on an i3 / 8gb ram / with nvidia GTX650
USB interface is connected to a USB3.0 port

Problem:
I have the motors tuned perfectly (I thought). I can jog all 5x axes smoothly and run Gcode flawlessly.
When I hit go to zero, sometimes, it will go to zero (all axes) but sometimes It will intermittently return to slightly off zero (0.0031 - working in mm) on some axes.
I have 1605 ballscrews on X&Y and 1204 on Z.
When the problem occurs (not always) it is consistently 0.0031 on both X&Y and consistently 0.0028 on the Z, leading me to believe this is fixable.
By (almost) all measures, the thing works... if it wasn't for those darn decimal points.

All cabling is shielded and I have triple checked all connections, reinstalled mach3, tried a different PC, tried 1/4 stepping and upped the amps on the TB6600s and a few dozen more things I could think of.

All this being said, I suspect most of you will write off my novusun controller as cheap rubbish - or perhaps my TB6600s. And I shall take this on the chin, as I had suspected as such from the get-go.
Unfortunately, I have invested considerable time and cash getting this enclosure off the ground, and I'd be forced to shed a tear as it tips sideways into the wheely bin.

Oh, and I cant for the life of me, get the analogue MPG wired to the novusun NVUM to work - if anybody has some pics from a successfully wired one, I'd love to see them... before I toss the lot.

Thanks!
Giffster