Actually, the feedrate, rpm and # of flutes are dependent on the chip load.Is the chip load only dependant on the feedrate, RPM, and number of cutting surfaces (flutes)?
The tool manufacturer should tell you what the recommended chip load should be. You then adjust rpm and feedrate to obtain that chip load. Be aware that it can be difficult to obtain a proper chip load on a homebuilt machine, especially with larger tools, as proper chiploads can require large cutting forces and high spindle power. Taking shallower cuts can alleviate these issues, but cause more wear on the tip of the tool.
As bit diameter increases, so does chip load. But it's not proportional. Chip load increases gradually as diameter increases.
No.The formula does not take into account the bit size? The reason I ask is that I know intuitively that with smaller bits, I should increase the RPM. But in theory, should I increase the RPM so that the outer edge of the bit matches that of a larger bit that I know I cut successfully with?
The chipload for a 1/8" tool is similar to that of a 1/4" tool, so if you double the rpm, you need to double the feedrate. You don't keep increasing feedrate as bits get smaller. It's usually the opposite. The larger the tool, the faster you can go, because the larger tools are stronger.For example, I'm using a 1/4" spiral-o-flute upcut bit, at about 15K RPM, and 40-45ipm, at .080 depth. Does this mean that I should run a similar 1/8" bit at 30K RPM and keep the feedrate constant, or keep the same RPM, and lower the feedrate by half? Is it directly proportional, as the formula suggests, or am I missing something?
Not sure with aluminum, but with wood, you should use the lowest rpm that gives an acceptable surface finish. The higher the rpm's, the more heat that is generated. Heat is the enemy of tooling. So lower rpm's generally are better.
As you decrease rpm, though, at some point, the finish quality will deteriorate.
Bottom line, is to follow the manufacturers chip load whenever possible. It's OK to use your gut feeling for rpm, but the feedrate needs to be correct for whatever rpm you choose, to achieve the recommended chip load.