I would stay away from these low RPM spindles if you want to mill aluminum. I’ve seen most of these being listed at 12000 rpm or below.
Theory
Chip behavior depends on the surface speed the cutter moves at. In a nutshell at lower speeds, there is more plastic deformation that requires more force to overcome while at higher speeds the behavior is more like a brittle break. Cutting forces and temperatures tend to raise steadily before that threshold is reached, then fall off once the chip behavior changes. This happens with most metals, however with soft aluminum alloys the drop is especially sharp. There is a diagram from a study done long time ago in this article. Later research confirmed that using badass methods such as shooting workpieces at cutting edges and filming the behavior.
Why this matters? Because cutter surface speed (sfm) is directly dependent on the RPM and the diameter of the cutter SFM = .262 * D * RPM
Let’s plug in some numbers.
500W spindle: .262 * 0.125 * 12000 = 384 sfm
DW660: .262 * 0.125 * 30000 = 960 sfm
For aluminum 1200 sfm is a recommended value for small cutting tools. Thus DW660 gets you a lot closer to that.
Practice
- Kevin’s build featured in the Aluminum Guide uses DW660.
- There is a report in the forum claiming Makita is way better than the 500W spindle