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Tips for CNC Router Aluminum Cutting Success

Updated: Aug 31

Tips for CNC Router Aluminum Cutting Success
CNC Aluminum Cutting Success

Today they I was asked "what materials can’t be used in a CNC machine?" My response was "CNC machines cut through nearly any material you can think of."

What’s your idea?

While there are a wide range of materials you can use in a CNC machine, the most commonly employed materials used are:

  • Metals — such as aluminum, brass, or steel.

  • Plastics — numerous choices such as Acetal (POM), Acrylics (PMMA), Polycarbonate (PC), and Polypropylene (PP), just to name a few.

  • Wood — usually less to choose from but commonly hardwood, plywood, softwood, etc.

  • Foam — tend to be more lightweight yet durable. The two main types are carving foam and rigid foam.

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.

Here are 7 tips for CNC Router Aluminum Cutting Success:

1. Take your time.

Material removal rates will be slower than those on a mill, but since most CNC routers handle material larger than a standard mill, the speed to size ratio is a good trade-off. So for high-quality work, slow down your removal of material

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. Avoid overly slow feed rates. By slowing the feed rate too much, you run the risk of making your tool rub instead of cut. Because the spindle is going so fast, this is can be a larger risk for CNC router users than for mill users.

3. Choose the proper router bit.

Use a 2 or 3 flute carbide endmill. They allow for a higher spindle speed on your router. Avoid cobalt and HSS cutters for working with aluminum.

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. Use smaller diameter cutters.

Forget about 1/2″ endmills and go to 1/4″ or smaller. This allows higher feed rates and makes for smoother cuts.

6. Clear your chips.

Keeping the chips clear of the cutter will avoid breaking endmills. If available, before working, use an air blast aimed at the point of the endmill cut. This will keep your cut clear of chips that can build up and break your cutter.

7. Examine Cut Depths and Slotting-they make it harder to clear chips.

Chips become harder to clear as you cut deeper and closer to a slot. Here’s a tip. 

When working with a material that has a thin sheet of aluminum bonded to it, set the sheet with the aluminum side up.  That makes it easier to get the aluminum cleared away from the cutter as quickly as possible.

8. 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.

9. Don’t slow down the feed rate too much!

If you go too slowly on your feed rate, 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.

10. 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.

11. CNC Router Aluminum Sheet Work is different than CNC Routers cutting Aluminum Plate.

There’s a world of difference for a CNC Router cutting thin aluminum sheet vs a CNC Router cutting thicker aluminum plate. The thicker the material and the greater the depth of cut, the more important it is to follow these tips.

Conclusion for CNC Router Cutting Aluminum:

Machining Aluminum with a CNC Router is absolutely doable with almost 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 the wise selection of tooling and cutting parameters.

If you any interested in CNC Router Cutting Machines, welcome to contact us, more information will be sent.

We reference Bob Warfield of CNC Cookbook and craft cloud post-amazing articles.

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