diff --git a/involute_gears.scad b/involute_gears.scad
index 9093283..a2866ab 100644
--- a/involute_gears.scad
+++ b/involute_gears.scad
@@ -295,31 +295,35 @@ module involute_bevel_gear_tooth (
 
 module gear (
 	number_of_teeth=15,
-	circular_pitch=false, diametral_pitch=false,
+	circular_pitch=undef, diametral_pitch=undef,
 	pressure_angle=28,
-	clearance = 0.2,
+	clearance = undef,
 	gear_thickness=5,
-	rim_thickness=8,
-	rim_width=5,
-	hub_thickness=10,
-	hub_diameter=15,
-	bore_diameter=5,
+	rim_thickness=undef,
+	rim_width=undef,
+	hub_thickness=undef,
+	hub_diameter=undef,
+	bore_diameter=undef,
 	circles=0,
 	backlash=0,
 	twist=0,
 	involute_facets=0,
 	flat=false)
 {
-	if (circular_pitch==false && diametral_pitch==false)
+	// Check for undefined circular pitch (happens when neither circular_pitch or diametral_pitch are specified)
+	if (circular_pitch==undef)
 		echo("MCAD ERROR: gear module needs either a diametral_pitch or circular_pitch");
 
 	//Convert diametrial pitch to our native circular pitch
-	circular_pitch = (circular_pitch!=false?circular_pitch:180/diametral_pitch);
+	circular_pitch = (circular_pitch!=undef?circular_pitch:pi/diametral_pitch);
+
+	// Calculate default clearance if not specified
+	clearance = (clearance!=undef?clearance:0.25 * circular_pitch / pi);
 
 	// Pitch diameter: Diameter of pitch circle.
-	pitch_diameter  =  number_of_teeth * circular_pitch / 180;
+	pitch_diameter  =  number_of_teeth * circular_pitch / pi;
 	pitch_radius = pitch_diameter/2;
-	echo ("Teeth:", number_of_teeth, " Pitch radius:", pitch_radius);
+	echo (str("Teeth: ", number_of_teeth, ", Pitch Radius: ", pitch_radius, ", Clearance: ", clearance));
 
 	// Base Circle
 	base_radius = pitch_radius*cos(pressure_angle);
@@ -342,8 +346,17 @@ module gear (
 	half_thick_angle = (360 / number_of_teeth - backlash_angle) / 4;
 
 	// Variables controlling the rim.
+	rim_thickness = (rim_thickness!=undef?(rim_thickness!=0?rim_thickness:gear_thickness):gear_thickness * 1.5);
+	rim_width = (rim_width!=undef?rim_width:root_radius * .1);
 	rim_radius = root_radius - rim_width;
 
+	// Variables controlling the hub_diameter
+	hub_thickness = (hub_thickness!=undef?(hub_thickness!=0?hub_thickness:gear_thickness):gear_thickness * 2);
+	hub_diameter = (hub_diameter!=undef?hub_diameter:root_radius * .3);
+
+	// Variables controlling the bore
+	bore_diameter = (bore_diameter!=undef?bore_diameter:root_radius * .1);
+
 	// Variables controlling the circular holes in the gear.
 	circle_orbit_diameter=hub_diameter/2+rim_radius;
 	circle_orbit_curcumference=pi*circle_orbit_diameter;
@@ -736,4 +749,3 @@ module test_backlash ()
 	translate([0,0,-5])
 	cylinder ($fn=20,r=backlash / 4,h=25);
 }
-