7 Tips for CNC Router Aluminum Cutting Success

7 Tips for CNC Router Aluminum Cutting Success

Folks often ask whether a CNC Router can cut aluminum. They’re used to seeing the primarily cut wood and plastics. My answer to this question is always, “Yes, if you do it right.” CNC Router machines are suitable for fabricating with wood, plastic, aluminum and more.

There are a couple of things to remember about how aluminum is different from wood or plastics. First, they have a much smaller “sweet spot” for optimal feeds and speeds. If you leave the sweet spot, cutters start breaking, wearing out a lot faster, and surface finish is poor at best. In fact, there are several sweet spots depending on what you want to accomplish: Metals have much smaller sweet spots (narrower range of acceptable feeds and speeds) than wood or plastics. The second thing is that for aluminum, there is a “stickiness” factor. Aluminum wants to stick to the tool. In fact, it will do so to the point that it welds itself to the tool. Once you have gummy aluminum deposits on your cutting edges, that tool is not long for this world, especially not at 20,000 rpm or more. Despite these challenges, you can cut aluminum very successfully on almost any router.

Here are 7 tips for CNC Router Aluminum Cutting Success:

1. Don’t be in a hurry A CNC Router Machine can cut aluminum, but it isn’t the ideal tool for hogging out big aerospace parts like wing spars. The price you’ll pay for success is slowing things down. Note that I don’t mean to literally slow down your feeds and speeds, but your overall Material Removal Rates will be less than what can be achieved with a purpose-built CNC mill. So relax and let the machine do its thing. At the very least, a good sized CNC Router can fit a lot more material on its table than most any CNC mill. Load it up, press the green button, and walk away.

2. Use matched Feeds and Speeds One of the issues for most CNC Routers is the spindle goes fast compared to a lot of CNC mills. Your average new CNC mill maxes out at 10,000 rpm and many CNC Routers can’t go that slow. Life for them begins at circa 20,000 rpm. The next couple of tips focus on solutions for this problem.

3. Use carbide coated cutters bits One way to bump up the recommended rpm is to be sure you’re using cutters that are happy going that fast. The measurement that determines this is called Surface Speed (for more on this and many other feeds and speeds hints and tips). Carbide cutters can go much faster than HSS cutters. Forget HSS and Cobalt for the most part. A coating, such as TiAlN allows the cutter to go even faster. Shop for carbide TiAlN coated cutters. They cost a little more, but they can change your results so much it’s darned well worth it. For example, say I need to cut a slot using a 1/4” endmill. If I select an HSS Endmill, G-Wizard tells me it wants to run 5877 rpm and my 20,000 rpm router spindle won’t go that slow. So I switch to a TiAlN Carbide Endmill. Now the recommendation is 16897 rpm–we’re much closer. This is with a Surface Speed of 1106 SFM. You may be able to find a more aggressive SFM recommendation for your manufacturer’s tooling. With aluminum, I’d go ahead and try 20,000 rpm for this cut. It’ll probably be just fine.

4. Use smaller diameter cutters The other way to bump up the rpms is to use smaller diameter cutters. Forget about 1/2″ endmills. Drop down to 1/4″ maximum and typically less. Because you’re going to smaller diameters, you want more rigid cutters lest tool deflection starts to be a problem. Carbide is much more rigid than HSS, so this is one more reason to favor carbide. The moral of the story is to carefully match your tooling to the capabilities of your machine.

5. Lubricate with a Mist Provide lubrication to cut down on the tendency for the chips to stick to the cutting edges. You pretty much have to use some kind of lubricant. In fact, buy a mister to provide air blast and coolant mist. It’s easy and inexpensive. Sometimes, it just isn’t possible to use mist but you still need to cut some aluminum. If you’re cutting very thin aluminum, or taking very shallow passes, you may be able to get by without lubrication. Do some tests and see.

6. Don’t slow down the feedrate too much! If you go too slowly on your feedrate, you run the risk of making your tool rub rather than cutting. This is a much bigger risk for CNC Router users than mill users simply because the spindle is going so fast. In order to maintain recommended chip-loads with rpms that high you’ll have to keep the cutting moving smartly. Our 3/16” cutter at 21000 rpm wants to feed at 91 IPM, for example. If you slow down too much, say to 1/4 of that, many will think they’re babying the machine and tool. Nothing could be further from the truth. If you wind up going slow enough that the cutter starts rubbing at 20K rpm, you’re going to heat up the whole works and drastically shorten your tool life.

7. If your CNC machine can’t feed fast enough, use fewer flutes and increase cut width Normally, we use 3 or fewer flutes with aluminum anyway–don’t try a four or more flute cutter in aluminum! The reason is that aluminum produces especially large chips. The fewer the flutes, the more space between the cutting edges, and the more room for the big chips to escape and be blown away. With too many flutes, the chips back in too tightly, jam up the flutes, and pretty soon you have a broken cutter.

Conclusion for CNC Router Cutting Aluminum: Machining aluminum with a CNC Router is absolutely doable with most any router. It’s just a matter of matching your machine’s capabilities to the “sweet spot” feeds and speeds requirements of the material through wise selection of tooling and cutting parameters.

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