Before moving and cutting a block, the CNC machine needs to know where to start, the start position is the part zero used in programming. In this article, here are three ways for how to set zero point in CNC or how to zero a CNC mill with stock before machining.
Parts zero is the datum corresponding to the 0, 0 coordinate on the CAD drawing, used to create g-code and complete other CAM work, in the g-code program, the X0Y0Z0 represents the location of part zero. The g-code commands are the instruction to tell the CNC machine what to do in the machining and cutting process, including guide the spindle to move specific distances in each axis, all these movements need a known starting position, which is the Part Zero. It can be any location in the workspace, but X/Y is usually set to one of the four corners of the work material, or the center of the work material, and Z home position is usually set to either the top surface of the work material or the bottom of the work material. CAD software will generate g-code according to the given zero location. For a typical 3-axis machine, g-code will contain instructions to move X (left/right), Y (front/back) and Z (up/down) in precise distance.
Choose a type of metal (steel, aluminum, or others) as the stock and tighten it in the vise. Use a hammer to hit the stock and the handle, repeat as necessary to ensure the stock and the parallels underneath can’t move, parallels are also up against the vise. Use some other parallels to properly raise your stock up from the vise for through holes. There are three ways to set an origin on the part in CNC.
1. Use a drill chuck and a pointer
The first method of CNC milling part zeroing is better to use when you have ample material. Scribe two lines on your stock on where you want your origin to be, then move your pointer over the intersection on what you think is close enough, finally to zero the X and Y axis (press X and Y).
2. Touch the stock slightly with an end mill
This technique is faster than the first one. You do not need to remove and insert a drill chuck with the pointer, after the end mill is lowered and ready to cut your part. For zeroing the X-axis, turn on the milling machine and slowly move the end mill into the direction of the X-axis towards the part, and stop when you see a small puff of metal shavings, and zero the X-axis by pressing X. But considering the tool offset, which is the radius of the end mill, after raising the end mill above the part we can move in the x-direction towards the part by a distance equal to the radius, then zero the X-axis by pressing X and absolute set, you will need to repeat this entire process to zero the Y-axis.
3. Use an edge finder
The third one is the most common and accurate way to locate part zero on the CNC machine. The edge finder also uses the drill chuck, so with the edge finder, properly set up next to your part, ready to turn on the machine, poke the edge finder so that it’s off-center and then slowly coming to the part, note it will appear to become one piece and then shift to the left, this indicates we’re finally touching the part and ready to zero. Zero the Y-axis by pressing Y. Similar to the second method, when using the end mill we need to consider the tool offset, first raise the edge finder above the part then move in its radius then zero the Y again by pressing Y.
For locating your part zero on CNC machines, there are other modern tools and techniques that can be used, such as 3D Taster, a Camera or Scope, Laser Sight, CNC probe, and more.