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The Little Things - A Mini Mill Article: Part 1

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It’s the little things.

It’s the little things.
Many times in life it’s the little things that make the biggest difference. The same goes for machining in many ways. You could have the best benchtop milling machine or lathe in the world, but if you don’t consider the “small” details of the machining process, you will never be able to produce a well machined part. Not to say that the quality of your mill itself is not important, because it is and without a rigid high quality milling machine, all the tips and tricks in the world will not get you better results.
I would like to briefly go over one of the most important and frustrating aspects of milling, especially for people new to machining and that is end mills, feeds and speeds.

End Mills, Feeds and Speeds
Using the correct end mills/cutters on your mini mill is extremely important. With all the styles, brands, coatings and material differences available, the task of finding the best end mills for your 3, 4 or 5-axis CNC benchtop milling application is not always easy and can be overwhelming at times.
To keep it simple, a good rule of thumb is to use 2 flutes for aluminum and 3 or 4 flutes for Stainless Steel. Aluminum machines are better with a heavier chip load so 2 flute end mills work best compared to stainless steel which machines best with a smaller chip load. So how does a 4 flute end mill make a smaller chip load compared to a 2 flute when machining on a mini mill? By increasing the flutes on an end mill, you are increasing the number of times the cutter makes a cut into the material per revolution. This means that a 4 flute end mill takes twice as many cuts in one revolution than a 2 flute end mill. As a result, it decreases the chip load per tooth by 50%.
Another way to look at it is to consider a milling machine that is milling at a given feed rate, let’s say 40 IPM, with a 2 flute end mill rotating at 1500 rpm creating a chip load of .1mm per tooth. If we change out the cutter with a 4 flute and keep the rpm at 1500 and the feed rate at 40 IPM than the chip load will decrease to .05mm per tooth. We could also achieve the .05mm chip load with the 2 flute end mill by increasing the rpm to 3000 or decreasing the feed rate to 20 IPM.
To some the above information probably sounds very confusing, and it did to me as well until I started testing and researching. Thankfully there are a lot of resources to help us figure out what the best cutter is for a specific material and what types of feeds, speeds and chip loads work best for those materials.
Please continue reading the second half of this article in Part 2 below.

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