Climb Milling with Bantam Tools Desktop CNC Machines
When programming the path your end mill takes through the workpiece, there are two strategies to choose from: climb milling and conventional milling. As with many aspects of CNC machining, the strategy you choose depends on a number of factors, such as:
The type of machine you’re using (CNC machine vs. manual mill or large production machine vs. desktop machine)
The type of material you’re cutting
The feature you’re milling
In most cases, climb milling is the preferred choice when working with modern CNC machines, like the Bantam Tools Desktop CNC Milling Machine and Bantam Tools Explorer™ CNC Milling Machine. Using climb milling with desktop CNC machines extends tool life, optimizes machine performance, and results in better surface finishes. Let’s take a closer look at these strategies to understand why.
Climb Milling vs. Conventional Milling
The difference between these two strategies is the cutter rotation and the direction of the feed. During climb milling, your cutter rotates in the same direction as the feed, while during conventional milling, the cutter rotates in the opposite direction of the feed.
Climb milling is beneficial because it reduces cutting pressure and produces less heat, which results in superior surface finishes. The cut strategy starts with the maximum chip thickness and then decreases over the course of the cut, causing heat to transfer into the chip instead of the workpiece. Additionally, because the tool is rotating in the same direction as the feed, the chips are evacuated behind the tool (away from the cutting path.
On the other hand, conventional milling is good for machining rough surfaces (e.g., castings and forgings), as well as hardened, hot-rolled, or hard-coated materials. Additionally, it’s an ideal cutting strategy if you’re using a manual mill (more on this below).
With conventional milling, the tool enters the workpiece at a shallow depth and then finishes with a deep cut. This puts a lot more pressure on the end mill and causes the heat to transfer into the workpiece, which can cause work hardening. Because the end mill is rotating in the opposite direction of the feed, the chips are evacuated in front of the tool (into the cutting path), so the end mill has to machine both new material and the evacuated chips and that means you’ll get a rougher surface finish.
Given these pros and cons it seems like conventional milling doesn’t make much sense, which may have you wondering, “If climb milling is more common for modern machines and more beneficial, why is conventional milling called ‘conventional’?” Glad you asked.
A Brief History of Conventional Milling
Back in the day (way before CNC machines were even conceivable), conventional milling was the only way to mill something. Old-fashioned manual machines needed to cut using this strategy because of backlash—the clearance or “slop” between the lead screw that drives a machine axis and the nut riding on the lead screw that turns it into linear motion. The force generated during conventional milling keeps the nut pressed against the lead screw, so the machine's axis remains stable.
Using a climb milling strategy on a machine with backlash, with anything other than very light cuts, results in a lot of motion because the cutting force is actually pulling away from the nut. This excessive motion could result in chatter, a damaged workpiece, a ruined end mill, damage to the machine, or even an injured machine operator. The good news is that modern CNC machines account for this backlash with things like anti-backlash nuts and, in turn, are now better suited for climb milling.
Working with Desktop CNC Machines
Therefore if you’re looking to optimize the performance of your Bantam Tools milling machine, extend the life of your end mills, and achieve great surface finishes, climb milling is the way to go.
Our Bantam Tools milling machines, like other professional CNC machines, are optimized for climb milling. But it’s important to remember that it’s not a 1:1 comparison between aerospace-grade CNC machines and our Bantam Tools milling machines—even if they are prototyping powerhouses. One way we’ve optimized our desktop CNCs for climb milling is by gearing more power toward the spindle motor rather than to the motors that drive the linear axes because climb milling allows the spindle to help pull the end mill through the cut. Because our desktop CNC machines punch above their weight class when it comes to build volume (among other machine specs), the power matchup and cutting forces between climb and conventional milling becomes even more prevalent. For instance, putting a 7" x 9” x 3.3" piece of aluminum in our Bantam Tools Desktop CNC Milling Machine is like putting a refrigerator-size piece of aluminum into a Mazak!
For certain toolpaths in Fusion 360 (e.g. the 3D adaptive pass) climb milling is the default. However, this is not necessarily the case for all toolpaths. So the next time you’re programming your part, be sure to select climb milling to ensure optimal machine performance, to prolong the life of your end mills, and to get an awesome surface finish.
At Bantam Tools, we build desktop CNC machines with professional reliability and precision to support world changers and skill builders. For the latest Bantam Tools news, sign up for our newsletter. If you’re interested in adding a Bantam Tools machine to your workflow you can order directly from our online store or request a quote.