The Math of Machining

FPR = 0.0878*?^4 - 0.1981*?^3 + 0.136*?^2 - 0.0159*? + 0.0042

Something I've really enjoyed since I started BetterCNC is getting to dive into some of the nitty gritty of machining that I've never had the resources to do before.

While we're still transitioning to carbide drills, we're working with our existing inventory of cobalt drills. The formula above is how I determine the feed rate for drilling in aluminum up to a 1" drill. And I have a similar formula for every other type of material. This is something I had never put much thought to over the years. Something that now I realize would have saved so much time in my career had I figured this out early on.

Prior to this, I was trained on some very basic numbers to use when drilling in various materials, but for the most part it was just experiment, find something that didn't burn up the drill and use that every time. The rule was to play it safe. So most of the time, I'd find a comfortable rpm and feed rate for my tooling and just stay there. Everywhere I've worked, that was typically the case for every programmer. Every programmer would have a slightly different number, but it was a tried and true number for them. A program from one employee may be different than the next, but they all built good parts, albeit at different cycle times.

Now that I use a CAM program that has the ability to store all of these cutting recipes, I've been diving deeper and deeper into the science of machining. Instead of using a comfortable cut recipe, why not find the fastest possible cut recipe? I've now gathered and built a variety of reference documents so I am no longer programming based on previous experience, I'm programming based on proven numbers. With this new found power, I'm feeding endmills and plunging drills faster than I ever have. Despite using the same types of tools that have been around since I started machining, I'm drilling holes 3-4 times faster than what I was 5 years ago. I'm roughing material 10 times faster than I did 10 years ago. Not that I was a slouch before, I take pride in the machinists I've scared with my aggressive programs over the years, but now I'm managing to scare myself and I love it!

My philosophy is to always find better ways of doing things. Sometimes this means to just experiment and find a better way, but if there are resources out there, following the math and science can be that much more beneficial. The next time you're programming a new part, think about how you came up with your cutting recipes. Is it a number that came from something, or is it just the tried and true you've always used?