– Incremental vs Absolute IJK: We’ve discussed IJK as offering coordinates relative to the starting point for the center. Here is a screen shot of the setup options: G-Wizard Editor let’s you specify several parameters in its Post that determine how arcs work. But there are controllers that don’t work exactly that way, so be sure you know what’s going on. In general, the rule is supposed to be that if you have both IJK and R in the same block, R takes precedence and IJK is ignored. This is another one of those places where lots of obscure things happen and you need to know what your controller will do without assuming anything. When IJK Are Not Incremental and What About Having Both IJK And R? Plus, Other Modal Shenanigans and Arc Variations It’s a good skill to be good at as a machinist! Variations in Arc Syntax for Different G-Code Dialects and Modes It’s kind of like being told you should only use the 4-jaw chuck on a lathe when you first start out so you’ll get very comfortable dialing it in. You’re going to need to be comfortable with relative coordinates anyway, as they’re darned handy. I say go with whichever approach makes sense for your particular situation, but you should definitely be familiar and comfortable with both. Personally, I don’t know if I agree with the CNC instructors that this is providing any extra checking or not. It has to chose a center that guarantees equal distance. In the case of the “R” format, the controller has no such double check. The check of each of those two distances is the double check. Once it has the center’s coordinates, it can check that it is equa-distant from both end points. Their argument is that when you use IJK, you get a double check that your arc is correct.īecause the controller gets to compute an actual set of coordinates for the center via IJK. But, the CNC teachers in the world will suggest that you should prefer IJK. Many of you will be deciding right here and now that since R is easier to understand and shorter to write, you’re just going to use R and forget about IJK. In this case, our circle has a radius of 2, so the g-code might be simply: We can also define the center just by specifying the radius of the circle. In other words, if we add the I value to the starting point’s X, and the J value to the starting point’s Y, we get the X and Y for the center.ĭefining the Center Via the Radius Using “R” The I and the J specify relative coordinates from the start point to the center. This arc starts at X0Y2 and finishes at X2Y0. The center is most commonly identified by using I, J, or K to establish relative offsets from the starting point of the arc to the center. The center is a bit more complex.ĭefining the Center Via IJK Relative Offsets The other may be established by XYZ coordinates. The current control point, or location when the block is begun establishes one endpoint. Once either the G02 or G03 mode is established, arcs are defined in G-Code by identifying their 2 endpoints and the center which must be equi-distant from each endpoint or an alarm will occur. G03 establishes a mode for counter-clockwise circular arcs. G02 establishes a mode for clockwise circular arcs. Like linear motion (initiated by G00 and G01), circular motion is a mode initiated via G02 or G03. Circular Motion is a Mode Initiated Via G02 and G03 If the machine has any backlash at all, it will be obvious at these reversals because there will be a glitch in the cut there. These would be the points corresponding to 0, 90, 180, and 270 degrees. Drawing a complete circle involves not just coordinated motion but reversal of direction at each of the 4 quadrant points. Circular interpolation is quite a bit more demanding on your machine as two axes have to be precisely coordinated. Other than the fairly exotic ability to follow a “NURBS” path, most g-code controllers only support two kinds of motion: linear and circular. Having just finished discussing linear interpolation, or motion in a straight line, we next come to circular interpolation, which is motion along a circular arc. Quick G-Code Arc Tutorial: Make G02 & G03 Easy, Avoid Mistakes Circular Interpolation is Motion Along a Circular Arc
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