HOW TO USE A G3 COUNTERCLOCKWISE ARC IN A CNC MILL PROGRAM

Hello and welcome back to lesson four in the series of Basic CNC Programming. In the previous lessons we have learned how to pick coordinates in a Cartesian coordinate system and how to determine their plus and minus values. And then in the last session we have learned how to use a G1 and a G2 in CNC programs. G1 being linear or straight line moves and G2 being clockwise arcs. So the next G code we're going to learn is a G3 and that would be counterclockwise arcs. So in this example we're going to use a half inch end mill again to walk around this part in a clockwise motion. This time we're going to start in the lower right hand corner and the origin is located in this lower left hand corner. And of course that's where X and Y is zero. Now notice as you're walking this radius the cutter pad makes a counterclockwise arc. So that would be where we would use a G3. Now what I would like you to do this time is pause the video and find the coordinates to the centerline in the tool as it walks around this part. You have enough dimensions here to determine the location of the tool. So let's spend a few minutes make a list of the start point and one through ten and then we'll come back and we'll compare coordinates. All right so let's take a look at the numbers real quick. We talked about the origin being right here at the lower left hand corner. Again that's where X and Y is zero. So our start position is 750 thousandths away from our three inch edge. So the centerline of that tool is sitting at 3 inches 750 Y minus 250 at the start point of the program. Then we're moving in a linear motion to position one right here. This edge is X zero and we're going to have to go a quarter inch past that edge to line up the side of the tool with this edge because that's what we're going to be cutting next. So X will be minus 0.250 and we were already sitting in So that's the coordinate for this position. Now again we're gonna do a linear move to position two as it's cutting this edge and we're gonna line up the bottom of the tool in line with this tangent of the radius. So we're still sitting at X minus 250 as we make that linear move and then we come up to Y one inch 500. Then we're going to make a linear move to get ready to swing a radius. Now there's no radius between here and here yet between two and three that's still a straight line move so that's going to still be a G1 to X zero. Notice the centerline of the tool is in line with this left edge where the origin is located and of course we're still sitting at Y 1.5. Now from this point three to four we're going to swing an arc a counterclockwise arc and the endpoint center point of the tool is in line with this top edge so that is Y two inches and the center point is sitting at X a half an inch. So then we need to position the tool to do a linear move across the top part here so the bottom edge of the tool will have to be lined up so that means we're going to move in a straight move to Y two inches 250 and of course our X stays the same. From five to six linear move we're going to go to X two inches 500 again getting that left edge of the end mill in line with our next radius. We're going to make another linear move between six and seven to Y two inches and then we're going to do another counterclockwise arc to number eight where our X value is three inches Y back to one inch five. Next move from eight to nine linear move getting this edge lined up with this final edge to be cut so we're sitting at three inches 250 Y 1.5 and then we make one final pass machining this edge right here and we're so that's number 10. So compare your numbers to these and let's go plug these into our program. All right so here we are we have plugged in our numbers into a small program and we have placed G1s and G3s on the proper lines so let's go ahead and verify that our shape is looking good as we step through this program. So let's first of all get to our start point here it is and let's move on we're going to make a G1 move right here in a straight line that's looking good then up to where the radius is notice the straight line before and after the radius look at the top line straight line before and after the radius and our final shape right there that's looking good and looks like the G3 produced the correct shape. So now let's look and see what would happen if by accident we had put a G2 on this G3 line. So let's take a look and the machine is going to try and do a G2 arc or a clockwise arc it will still do it but of course the resulting shape is not what we intended. So let's go ahead and move these back to G3s counterclockwise arcs and that look that looks good. So you have learned G1s G2s and G3s and their proper use in the program. So thank you for watching and we'll see you in the next video.