So, if we need to helix down 1″, and we specified a 1/4″ DOC as we did for this example, it will take 4 rotations at these feeds and speeds to get to the bottom of the hole. The helix angle is based on the idea that the endmill will achieve the depth of cut specified in one rotation. G-Wizard tells us the ramp angle is 6.1 degrees and our adjusted feedrate should be 31 inches per minute, which is a little slower than the 43 IPM a straight slot calls for. Now press the “Interpolate” button to bring up the Interpolation Mini-Calculator.
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Set it with a full 1/2″ width of cut and let’s be a little conservative on depth of cut–we’ll use 1/4″. Say we have a 1/2″ carbide endmill and we’re cutting 6061 aluminum. Start out figuring feeds and speeds for slotting. We can use the G-Wizard CNC Calculator to figure it out: What should our feedrate be and what should the helix ramp angle be? Let’s assume we’ve decided to use helical interpolation. Helical Interpolation (aka Circular Ramping) That chip is dull and soon causes the tool to break as it grows during the cut. Often, the wrong kind of entry is microscopically chipping the tool. When people contact me about problems cutting tough materials like stainless steel, one of the first questions I ask is how the cutter entered the cut. So, a 2 flute cutter could plunge at 1/2 it’s slotting feedrate. A good rule of thumb is to divide the normal feedrate if slotting to the same depth by the number of flutes. The feedrate when plunging is typically a fraction of the normal straightline feedrate.
You can plunge with an endmill, but it is hard on it, chip evacuation is harder, you need a center cutting endmill and so on. Ramping means moving the cutter in a straight line while gradually increasing depth. If you’re not familiar with these methods, helical interpolation involves producing a circular hole by having the endmill describe a helical motion. I’ve seen this confirmed over and over again by a variety of sources, but I was prompted to pen this quick post while reading some guidelines for HSM by Robbjack. Helical Interpolation creates the least wear on the tooling, followed by ramping, and plunging is by far the least kind way of entering a cut for your tools. Leaving aside the possibility of pre-drilling a hole or other strategies that could involve a tool change, the pecking order is pretty straightforward. What’s the best way to get the cutter to depth when beginning a pocket? Helical Interpolation Ramp Angle Calculator: Best Ways to Enter a Cut