tighter which will change the position of lever 124 and enable the nut to be readily regulated by the thumb while holding the handling knob 74 thus forming a second handling means so as to regulate the contour guides 76 and 77 to pivot about pivot member 96 which enables reentrant portion 75 of the rear contour guide 77 to be moved back and forth in recess 81 in the housing portion 78 this will enable the lever 124 to be loosened and the handling knob 74 to be moved about the axis of pivot member or bolt 116 so the marker 130 on lever 114 will register with one of the indicia 132 to indicate whether contour guide members 76 and 77 are planar if positioned at zero or have a convex contour when positioned to one side of zero the guide members 76 and 77 will be concave when moved to the opposite side of zero and the lever 124 tightened to maintain the contour guide members 76 and 77 in the desired position to form the desired contour the housing 12 is split longitudinally along a line 15 which housing portions are held together by screws 17 to make possible the disassembly and reassembly of the housing 12 as will be seen in fig3 the inner side of each portion of the housing 12 has hardened metal or a composition element 133 secured thereto as by welding or cementing as indicated at 135 which element is in circumferential alignment with the abrasive sheet 53 to retain the abrasive sheet 53.