Going below zero

I just put together a Rostock Mini Pro. Until now I have been able to find my own answers. But this one has me stumped. I have calibrated the bed. And when I manually jog the position or use a macro the extruder goes to the right spot. But when I print the extruder hits the bed. If I remove the bed the extruder will go another 10mm and hit the bottom plate. I have been over all the tabs and settings and can not see where I went wrong. I have looked at the G-code and nothing jumps out at me. For the record I am using Simplify3D. Below is the first part of the G-code.

; increaseFanForBridging,0
; bridgingFanSpeed,100
; use5D,1
; relativeEdistances,0
; allowEaxisZeroing,1
; includeM10123,0
; stickySupport,1
; detectArcs,0
; arcReplaceG2G3,0
; arcRadialCompensation,1
; gcodeXoffset,0
; gcodeYoffset,0
; gcodeZoffset,0
; overrideMachineDefinition,0
; machineTypeOverride,1
; strokeXoverride,160
; strokeYoverride,160
; strokeZoverride,165
; originOffsetXoverride,80
; originOffsetYoverride,80
; originOffsetZoverride,0
; homeXdirOverride,0
; homeYdirOverride,0
; homeZdirOverride,1
; flipXoverride,1
; flipYoverride,-1
; flipZoverride,1
; startingGcode,G28 ; home all axes
; layerChangeGcode,
; toolChangeGcode,
; endingGcode,G28 X0 Y0 Z0 ;home,M104 S0 ; turn off extruder,M140 S0 ; turn off bed,M84 ; disable motors
; createX3G,0
; celebration,0
; celebrationSong,Random Song
; postProcessing,
; defaultSpeed,3600
; outlineUnderspeed,0.5
; supportUnderspeed,0.8
; rapidXYspeed,4800
; rapidZspeed,1000
; minBridgingArea,50
; bridgingExtrusionMultiplier,1
; bridgingSpeedMultiplier,1
; filamentDiameter,1.75
; filamentPricePerKg,46
; useMinPrintHeight,0
; minPrintHeight,0
; useMaxPrintHeight,0
; maxPrintHeight,0
; overlapRemoval,0
; overlapRemovalPercentage,0.3
; useDiaphragm,0
; diaphragmLayerInterval,20
; robustSlicing,1
; mergeAllIntoSolid,0
; onlyRetractWhenCrossingOutline,1
; retractBetweenLayers,1
; useRetractionMinTravel,0
; retractionMinTravel,3
; useRetractionOozeRate,0
; retractionOozeRate,100
; onlyWipeOutlines,1
G90 ; use absolute coordinates
M82 ; absolute extrusion distances
G21 ; set units to millimeters
M106 S0
M104 S190 T0
M109 S190 T0
G28 ; home all axes
G92 E0
G1 E-1 F1800
; layer 1, Z = 0.18
T0
; tool H0.2 W0.4
G0 X-18.99 Y5.168 F4800
G0 Z0.18 F1000
G1 E0 F540
G92 E0
G1 X-27.6 Y5.168 E0.2577 F1800

Before I start, note that I use Repetier-Host software with CuraEngine as the slicer. When running into issues with the Zero plane, I found that I just needed to calibrate my machine's Z-Axis (always a good place to start).

- If that isn't the issue then I may suggest making sure your units are declared (G21) & your machine is homed (G28) before setting the CSYS (G90) and extrusion distances (M82).

ONLY if your machine supports the @pause command, you may try the code below to help find where your machine looses location. Simply use a gauge or calipers at each pause to check if the extruder tip is actually moving to those specific heights.

G21 ; Set Units to MM
G28 ; Home extruder
G1 Z15 F1000 ; Check Z-Distance for 15mm
@pause Check Z-Distance 15mm
G90 ; Absolute positioning
M82 ; Extruder in absolute mode
M190 S50 ; Heat Bed
M104 T0 S200 ; Heat Extruder
G1 Z20 F1000 ; Check Z-Distance for 20mm
@pause Check Z-Distance 20mm
G92 E0 ; Reset extruder position
G1 Z15 F1000 ; Check Z-Distance for 15mm
@pause Check Z-Distance 15mm

Turned out that I had to change the Z_MAX constant in the RAMPS controller. Now that part is working fine. However I am going nuts trying to get the extruder to work, it is constantly jamming.

- Extruder jams that I've experienced are normally due to inconsistent filament size. If your feeding more material into the 'Hot End' than it can extrude successfully it starts to create a back up pressure that eventually jams the extruder.

Suggested test:
- On a few pieces try dialing the flow-rate down or increasing the filament size parameter a bit and see if that begins to alleviate the jamming.