around the pivot point 41 the receiver 40 may preferably be held at a desired angle relative to the base 40 through engagement of the pin 45 with the edge of the slot 43 or other suitable means which will be apparent to those skilled in the art in operation the apparatus 2 is presented to the obstacle 6 such that the obstacle 6 passes through the gap 20 into the open centered of the support 18 and is preferably positioned at or near the axis of rotation r the engager 22 then operatively connects the traveler 16 to the driver 50 permitting rotation of the traveler 16 about the support 18 as the traveler 16 slides along the support 18 a tool 15 mounted to the bracket 24 is moved around the perimeter 13 of the obstacle 6 preferably the engager 22 operatively engages the traveler 16 at least two points 26 shown on fig2 and 3 two of which points are separated by a distance at least equal to the difference between the length of the support and the length of the traveler in particular the traveler 16 is preferably no longer than the support 18 if it is desired for the traveler 16 to have full 360 u00b0 rotational capacity it is desirable that the traveler 16 operatively engage the engager 22 at two points which are sufficiently far apart to ensure that regardless of the position of the.