diff --git a/OpenbuildsGRBL.cps b/OpenbuildsGRBL.cps
index be2e78c..c85564e 100644
--- a/OpenbuildsGRBL.cps
+++ b/OpenbuildsGRBL.cps
@@ -17,6 +17,7 @@ This post-Processor should work on GRBL-based machines such as
 30/JAN/2017 - V6 : Modified capabilities to also allow waterjet, laser-cutting..
 */
 
+
 description = "Openbuilds Grbl";
 vendor = "Openbuilds";
 vendorUrl = "http://openbuilds.com";
@@ -49,9 +50,12 @@ properties =
 	spindleTwoDirections : false,		// true : spindle can rotate clockwise and counterclockwise, will send M3 and M4. false : spindle can only go clockwise, will only send M3
 	hasCoolant : false,					// true : machine uses the coolant output, M8 M9 will be sent. false : coolant output not connected, so no M8 M9 will be sent
 	hasSpeedDial : true,				// true : the spindle is of type Makite RT0700, Dewalt 611 with a Dial to set speeds 1-6. false : other spindle
+	wantHoming: false,					// do not home by default, can be dangerous
 	machineHomeZ : -10,					// absolute machine coordinates where the machine will move to at the end of the job - first retracting Z, then moving home X Y
 	machineHomeX : -10,
-	machineHomeY : -10
+	machineHomeY : -10,
+	fourAxis: false,					// enable four axis mode
+	makeAAxisOtherWay: false			// change direction of rotation of A axis
 	};
 
 // creation of all kinds of G-code formats - controls the amount of decimals used in the generated G-Code
@@ -60,6 +64,7 @@ var mFormat = createFormat({prefix:"M", decimals:0});
 
 var xyzFormat = createFormat({decimals:(unit == MM ? 3 : 4)});
 var arcFormat = createFormat({decimals:(unit == MM ? 4 : 5)});    // uses extra digit in arcs
+var abcFormat = createFormat({decimals:3, forceDecimal:true, scale:DEG});	// A axis is rotating, so set unit as degrees
 var feedFormat = createFormat({decimals:0});
 var rpmFormat = createFormat({decimals:0});
 var secFormat = createFormat({decimals:1, forceDecimal:true});
@@ -68,6 +73,9 @@ var taperFormat = createFormat({decimals:1, scale:DEG});
 var xOutput = createVariable({prefix:"X"}, xyzFormat);
 var yOutput = createVariable({prefix:"Y"}, xyzFormat);
 var zOutput = createVariable({prefix:"Z"}, xyzFormat);
+var aOutput = createVariable({prefix:"A"}, abcFormat);
+var bOutput = createVariable({prefix:"B"}, abcFormat);
+var cOutput = createVariable({prefix:"C"}, abcFormat);
 var feedOutput = createVariable({prefix:"F"}, feedFormat);
 var sOutput = createVariable({prefix:"S", force:true}, rpmFormat);
 
@@ -144,7 +152,17 @@ function writeComment(text)
 	}
 
 function onOpen()
-	{
+{
+	if (properties.fourAxis) {
+        // Create the fourth axis
+        // See page 23 of https://github.com/AutodeskCAM/Documentation/blob/master/Autodesk%20Post%20Processor%20manual-sm-130829.pdf
+		var aAxis = createAxis({coordinate:0, table:true, axis:[(properties.makeAAxisOtherWay ? -1 : 1) * -1, 0, 0], cyclic:true, preference:1});
+		machineConfiguration = new MachineConfiguration(aAxis);
+
+		setMachineConfiguration(machineConfiguration);
+		optimizeMachineAngles2(1); // map tip mode
+	}
+
 	// Number of checks capturing fatal errors
 	// 1. is CAD file in same units as our GRBL configuration ?
    // swarfer : GRBL obeys G20/21 so we should only need to output the correct code for the numbers we are outputting, I will look at this later
@@ -165,6 +183,9 @@ function onOpen()
 	// 2. is RadiusCompensation not set incorrectly ?
 	onRadiusCompensation();
 
+	bOutput.disable(); // five and six axis not yet supported
+	cOutput.disable();
+
 	// 3. here you set all the properties of your machine, so they can be used later on
 	var myMachine = getMachineConfiguration();
 	myMachine.setWidth(600);
@@ -303,7 +324,7 @@ function onSection()
 		writeBlock(gAbsIncModal.format(90));	// Set to absolute coordinates
 		if (isMilling())
 			{
-			writeBlock(gFormat.format(53), gMotionModal.format(0), "Z" + xyzFormat.format(properties.machineHomeZ));	// Retract spindle to Machine Z Home
+			if(properties.wantHoming) writeBlock(gFormat.format(53), gMotionModal.format(0), "Z" + xyzFormat.format(properties.machineHomeZ));	// Retract spindle to Machine Z Home
 			}
 		}
 
@@ -359,15 +380,22 @@ function onSection()
 	forceXYZ();
 
 	var remaining = currentSection.workPlane;
-	if (!isSameDirection(remaining.forward, new Vector(0, 0, 1)))
+	if (!properties.fourAxis && !isSameDirection(remaining.forward, new Vector(0, 0, 1)))
 		{
-		alert("Error", "Tool-Rotation detected - GRBL only supports 3 Axis");
-		error("Fatal Error in Operation " + (sectionId + 1) + ": Tool-Rotation detected but GRBL only supports 3 Axis");
+		alert("Error", "Tool-Rotation detected - GRBL ony supports 3 Axis or fourAxis is false");
+		error("Fatal Error in Operation " + (sectionId + 1) + ": Tool-Rotation detected but GRBL ony supports 3 Axis or fourAxis is false");
 		}
 	setRotation(remaining);
 
 	forceAny();
 
+	// Move A axis first if needed
+	if (properties.fourAxis) {
+        // See page 24 of https://github.com/AutodeskCAM/Documentation/blob/master/Autodesk%20Post%20Processor%20manual-sm-130829.pdf
+		var abc	= machineConfiguration.getABC(currentSection.workPlane);
+		setRotation(machineConfiguration.getRemainingOrientation(abc, currentSection.workPlane));
+		writeBlock(gMotionModal.format(0), aOutput.format(abc.x));
+	}
 	// Rapid move to initial position, first XY, then Z
 	var initialPosition = getFramePosition(currentSection.getInitialPosition());
 	writeBlock(gAbsIncModal.format(90), gMotionModal.format(0), xOutput.format(initialPosition.x), yOutput.format(initialPosition.y));
@@ -434,14 +462,44 @@ function onLinear(_x, _y, _z, feed)
 
 function onRapid5D(_x, _y, _z, _a, _b, _c)
 	{
-	alert("Error", "Tool-Rotation detected - GRBL only supports 3 Axis");
-	error("Tool-Rotation detected but GRBL only supports 3 Axis");
+	var x = xOutput.format(_x);
+	var y = yOutput.format(_y);
+	var z = zOutput.format(_z);
+	var a = aOutput.format(_a);
+	var b = bOutput.format(_b);
+	var c = cOutput.format(_c);
+	if (x || y || z || a || b || c)
+		{
+		writeBlock(gMotionModal.format(0), x, y, z, a, b, c);
+		feedOutput.reset();
+		}
 	}
 
 function onLinear5D(_x, _y, _z, _a, _b, _c, feed)
 	{
-	alert("Error", "Tool-Rotation detected - GRBL only supports 3 Axis");
-	error("Tool-Rotation detected but GRBL only supports 3 Axis");
+	var x = xOutput.format(_x);
+	var y = yOutput.format(_y);
+	var z = zOutput.format(_z);
+	var a = aOutput.format(_a);
+	var b = bOutput.format(_b);
+	var c = cOutput.format(_c);
+	var f = feedOutput.format(feed);
+
+	if (x || y || z || a || b || c)
+		{
+		writeBlock(gMotionModal.format(1), x, y, z, a, b, c, f);
+		}
+	else if (f)
+		{
+		if (getNextRecord().isMotion())
+			{
+			feedOutput.reset(); // force feed on next line
+			}
+		else
+			{
+			writeBlock(gMotionModal.format(1), f);
+			}
+		}
 	}
 
 function onCircular(clockwise, cx, cy, cz, x, y, z, feed)
@@ -502,7 +560,7 @@ function onClose()
 	writeBlock(gAbsIncModal.format(90));	// Set to absolute coordinates for the following moves
 	if (isMilling())
 		{
-		writeBlock(gAbsIncModal.format(90), gFormat.format(53), gMotionModal.format(0), "Z" + xyzFormat.format(properties.machineHomeZ));	// Retract spindle to Machine Z Home
+		if(properties.wantHoming) writeBlock(gAbsIncModal.format(90), gFormat.format(53), gMotionModal.format(0), "Z" + xyzFormat.format(properties.machineHomeZ));	// Retract spindle to Machine Z Home
 		}
 	writeBlock(mFormat.format(5));																					// Stop Spindle
 	if (properties.hasCoolant)
@@ -510,7 +568,7 @@ function onClose()
 		writeBlock(mFormat.format(9));																				// Stop Coolant
 		}
 	onDwell(properties.spindleOnOffDelay);																			// Wait for spindle to stop
-	writeBlock(gAbsIncModal.format(90), gFormat.format(53), gMotionModal.format(0), "X" + xyzFormat.format(properties.machineHomeX), "Y" + xyzFormat.format(properties.machineHomeY));	// Return to home position
+	if(properties.wantHoming) writeBlock(gAbsIncModal.format(90), gFormat.format(53), gMotionModal.format(0), "X" + xyzFormat.format(properties.machineHomeX), "Y" + xyzFormat.format(properties.machineHomeY));	// Return to home position
 
 	writeBlock(mFormat.format(30));																					// Program End
 	writeln("%");																									// EndOfFile marker