Folks often ask whether a CNC Router can cut aluminum. They’re used to seeing them primarily cut wood and plastics. My answer to this question is always, “Yes, any CNC Router can cut aluminum if you do it right.” I’m going to tell you EXACTLY how to cut aluminum with your CNC Router with these 11 easy tips.

Once you know the secrets, you’ll find machining aluminum with a CNC Router is not only easy, but very productive. Using a CNC Router for aluminum parts can be a very successful pursuit with a little care and preparation.

Manufacturer Onsrud suggests. This works particularly well for routers. Optimizing feed rates and speeds: 1. Start off using an RPM derived for the chip load for the material being cut (see charts). Increase the cutting speed (feed rate) until the quality of the part’s finish starts to decrease or the part is starting to move from hold downs. Feeds and Speeds Quick Guides 10 Tips for CNC Router Aluminum Cutting Success: Take these shortcuts and skip a lot of pain. Tips for Getting the Best CNC Milling Surface Finish: And the truth about mirror finishes. Feeds and Speeds for Fly Cutters and Manual Mills: Tips and tricks for using G-Wizard with Manual Mills.

But, there is no simple cutting speed formula available to give proper feeds and speeds for HSM. Before there were good HSM Feeds and Speeds Calculators like G-Wizard, you had to just look at a bunch of scenarios others published and try to pick one close to your situation.

There are a couple of things to remember about how aluminum (and other metals) are 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, they wear 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 acceptible feeds and speeds) than wood or plastics…

The second thing is that for aluminum (and some other metals), 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 10 tips for CNC Router Aluminum Cutting Success:

1. Don’t be in a hurry

A CNC Router 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 a Feeds and Speeds Calculator

Look, you’re going to approaching the limits of what your machine can do in all likelihood. Cutting aluminum on a CNC Router is not a cakewalk, so let’s do it right. None of this “cutting by ear” the old timers so love to talk about. The ear can’t keep up fast enough as your machine skates around corners and through pockets. One minute things are fine, the next you’re dodging the tip of the cutter that got broken off and flung across the shop. All CNC’ers can benefit from a Feeds and Speeds Calculator, but when you’re near the edge of the performance envelope, you want to be particularly careful. Of course we recommend our own G-Wizard Feeds and Speeds Calculator. There are certainly others out there as well, but ours is the world’s first feeds and speeds calculator especially designed for the needs of CNC Router users (click that link to see why).

Make sure the one you get has the right features for CNC Routers. Very important features for CNC Routers that we include with G-Wizard Calculator include:

– Minimum rpm setting. The Calculator doesn’t help if it keeps telling you to go slower than you possibly can.

– CNC Router Cutter Types: V-Bits, compression bits, and downcut bits are all important for CNC Router users. Make sure your new calculator handles them like G-Wizard does.

– Deflection: Tool deflection is a fact of life and accounts for a lot of broken tools. Make sure your calculator will figure out the deflection and that it has capabilities like our Cut Optimizer and CADCAM Wizards to help find solutions that avoid excessive deflection.

– Rubbing Warning: If you slow down feedrates too much, your cutter quits slicing off nice clean chips and starts to plough along on the surface. This is called “rubbing” and really reduces tool life due to the heat it generates. Get a calculator that includes a rubbing warning.

– Chip Thinning: When you take light cuts whose width is less than half the diameter of the cutter, you get chip thinning. Your calculator needs to compensate for that or you’ll wear out the tools prematurely.

– Ability to derate horsepower for less rigid machines: See #10 below for more. It’s also nice if the calculator has multiple machine profiles so you can easily switch between full rating and derated profiles as needed.

Once you’ve got a calculator, your first problem will be dealing with the recommended rpms being too low. 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 CNC Router Bits for cutting aluminum (carbide endmills)

CNC Routers use a variety of specialized cutters that should not be used with aluminum. Downcut Spirals, Compression Cutters, and the like have no place in aluminum work.

You want cutters specifically made for aluminum. Most of the CNC world uses 2 or 3 flute carbide endmills for the purpose.

This helps to bump up the recommended rpm to be sure your cutters are happy going at the high rpms CNC Router Spindles operate at. The measurement that determines this is called Surface Speed (for more on this and many other feeds and speeds hints and tips, check out our Feeds and Speeds Cookbook). Carbide cutters can go much faster than HSS cutters. Forget HSS and Cobalt cutters for aluminum.

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 Carbide Endmill. Now the recommendation is 17419 rpm–we’re much closer. This is with a Surface Speed of 1140 SFM. You may be able to find a more aggressive SFM recommendation for your manufacturer’s tooling.

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–remember, you need a Feeds and Speeds Calculator that deals with tool deflection. Carbide is much more rigid than HSS, so this is one more reason to favor carbide.

Looking at our example in #3 of the carbide cutters, suppose that instead of a 1/4″ endmill, we are using a 3/16″. That seemingly small change has now kicked up the recommended rpm to 23226 rpm–prime router spindle territory. It’s easy for us to slow that down to 20K rpm and pick up a little extra tool life.

The moral of the story is to carefully match your tooling to the capabilities of your machine.

5. Be paranoid about clearing chips

I can’t stress this enough, especially when the material has an affinity to bond with the cutter.

Recutting chips breaks more cutters than most any other thing I see happening. Be paranoid about clearing the chips. Don’t count on a nearby vacuum dust collection system unless you have personally verified it sucks the chips out of even the deepest cuts. More reliable is an air blast fixed to the spindle and pointing right at where the cutter meets the material being cut. If you’re standing there, nozzle in hand (or worse a brush) thinking you can keep things clear, you’re not paranoid enough about clearing chips.

6. Watch cut depths and slotting–they make it harder to clear chips

The deeper you cut and the closer to a slot the cutter travels in, the harder it is to clear the chips out of the bottom of the hole. Make more passes to cut down to required depth and to open up the shallower depths for better access.

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.

7. Lubricate with a Mist

Assuming you’re suitably paranoid about those chips, the next issue is providing lubrication to cut down on the tendency for the chips to stick to the cutting edges.

Many CNC Router users are loathe to mess with coolant of any kind, but you pretty much have to use some kind of lubricant to cut anything but the thinnest aluminum reliably. Since you’ve presumably already rigged up a compressed air blast, you may as well run coolant mist through the same mechanism. In fact, buy a mister to provide air blast and coolant mist. It’s easy and inexpensive.

You can set the mist so very little fluid is deposited to reduce the mess, and that’s fine so long as what’s being sprayed is going on the cutter.

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.

8. Don’t slow down the feedrate too much!

If you go too slow 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 cutter moving smartly.

Our 3/16″ cutter at 21K 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. For more on this rubbing phenomenon, see our article on chip loads and surface speeds.

Being on top of rubbing problems is easy when you use a feeds and speeds calculator like G-Wizard that warns you about rubbing.

9. If your machine can’t feed fast enough, use fewer flutes and increase cut width

Normally, we use 3 or fewer flutes with aluminum anyway–just 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.

Let’s suppose you are using your feeds and speeds calculator, and you come up with a situation where your machine just can’t move the cutter fast enough. For example, taking our 3/16″ example at 21K rpm, let’s say we’re cutting an 0.040″ wide cut. G-Wizard suggests feeding a 3 flute endmill at 166 inches per minute, but your CNC Router can only cut accurately and reliably at 100 IPM. What to do?

Cnc Router Feeds And Speeds For Cutting 2.5mm Thick Aluminum Siding

The answer is to try fewer flutes. A 2 flute cutter only needs a feedrate of 110 IPM. Slowing that down to 100 IPM is not going to run a rubbing risk–it’s only 10% slower.

BTW, we’ve been talking about cutting aluminum, but you can hit this problem even worse with wood because you can cut the softer material so much faster. Plug in these values and select Hardwood in G-Wizard and it wants to go 883 IPM at 20,000 rpm!

Here’s a tip: they make 1 flute cutters for precisely this reason.

Cnc Router Feeds And Speeds For Cutting 2.5mm Thick Aluminum Foil

If we take the scenario down to a single flute at 20000 rpm GW now recommends 294 IPM. If you’re burning the wood, it’s probably because you’re feeding too slowly and the cutter is rubbing. BTW, I love watching a fast moving industrial CNC Router blasting through wood and shooting up a blizzard of chips and dust. Cool beans!

The other thing to be aware of is what’s called “Radial Chip Thinning“. If your cut width is less than 1/2 the cutter diameter, you need to speed up your feedrate because your machine is producing unnaturally thin chips due to Radial Chip Thinning. Here again, you think that by taking super thin cuts and slowing the feedrate down drastically. Instead, because of radial chip thinning and rubbing, you’re drastically reducing your cutter life. The G-Wizard Feeds and Speeds Calculator automatically factors in radial chip thinning to its calculations.

10. Use a Horsepower limit to derate for rigidity

Okay, you’ve mastered the other 9 tips, and things are going well, but you’re now running up against the rigidity limits of your machine. If you plow in with full power, bad things happen. The machine chatters and destroys the cutter, surface finish is lousy, or the machine deflects and cuts very inaccurately.

Cutting forces for metal are likely to be much higher than for wood and CNC Routers (sometimes called Gantry Mills) are considerably less rigid than equivalent CNC Mills. This is just a fact of life. If nothing else, compare the work envelope of the mill (much lower than a router) and it’s weight (much higher than a router) against a CNC Router. Except for the biggest industrial Gantry Mills, there is no comparison. And because of that, no way that machine is as rigid as a CNC Mill. So, we have to compensate.

We don’t know the exact rigidity of a given machine. There’s not a published spec we can use to compare or calculate from. But, we can use spindle power as a proxy. It is that power “pushing” against the workpiece while cutting, that the rigidity must fight. G-Wizard has the ability to calculate a “de-rated” spindle power that matches the work envelope and weight of your machine to a spindle power that is appropriate for that level of rigidity. The results may surprise you, but they’re based on real empirical measurements.

For example, suppose you have a 4′ x 8′ router with 20″ of Z travel that weighs 1000 lbs. Note that even a fairly lightweight commercial CNC mill, like a Haas TM-1, will have travels of 30″ x 12″ x 16″ and a total weight of 3240 lbs–a much smaller envelope and a lot more weight. To perform at this kind of level of rigidity (and a TM-1 is not exactly the pinnacle of rigidity either) requires derating horsepower to 0.17 HP.

Derating will take our numbers way down–22K rpm and 79 IPM for the full slot with a 3/16″ inch and a 2 flute. But, we’ll get the job done with better surface finish, accuracy, and less tendency to deflect the machine frame or chatter.

Don’t run derated all the time, keep a machine profile that is derated and one that is not. Use the derated one for finer surface finish or for cases where the cutter keeps breaking.

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

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. A good feeds and speeds calculator like our G-Wizard can help you do that. Add to that the need for lubrication and being paranoid about chips piling up and you’re ready to tackle an aluminum project.

CNC Router Aluminum Cutting FAQ

Can a CNC Router cut aluminum?

Absolutely! It’s a matter of using the right cutter or bit, the correct feeds and speeds, and avoiding various other pitfalls described in this article.

What’s the #1 reason CNC Routers fail to cut aluminum?

Lack of lubrication is the #1 reason CNC Routers fail to cut aluminum. Aluminum has a chemical affinity for the cutter that causes chips to weld onto the cutter if there is no lubricant. Read more in this article.

How can I get good cnc router speeds and feeds for aluminum?

Use a high quality feeds and speeds calculator made for CNC Routers. There are many issues peculiar to CNC Routers that must be considered for proper feeds and speeds.

What are the best CNC router bits for aluminum?

Use good quality carbide end mills with no more than 3 flutes.

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There are certain parameters that must be considered, before setting up any file for cutting if you are to accomplish the finish and accuracy required. One of the most important of these factors is the Chipload per Tooth (Cpt). Chipload can be defined as the size or thickness of the chip that is removed with each flute per revolution.
When material is machined the cutter must revolve at a specific RPM and feed at a specific feedrate to achieve the proper Chipload. There are also several factors to be considered when choosing the proper RPM and feedrate.
The feed rate used depends upon a variety of factors, including power and rigidity of the machine, rigidity of part hold-down, spindle horsepower, depth and width of cut, sharpness of cutting tool, design and type of cutter, and the material being cut.
To obtain the optimum Chipload, you must consider these variables, along with the machine and materials you intend to cut. This will help you find the best feed rate and RPM for any given tool and material.
One thing to remember is to make chips not dust. Chips will help by removing the heat produced in the cutting process thus increasing tool life and improving edge quality. Feeds and speeds are usually all set in the programming software that is used to create the machine program. There are many resources available to help determine suitable settings for particular material / router bit combinations.
These often provide a good starting point but can usually be further improved through a small amount of trial and error. Most machine controllers allow you to adjust the feed rate while a program is running and by listening to the sound the cutter makes this can be a good way of optimizing the parameters.
Feed rate is calculated using the following equation:
Feed = N x T x Z
N = number of cutting edges (flutes)
T= chip load (chip per tooth) is the amount of material, which should be removed by each tooth of the cutter as it rotates and advances into the work. (mm per tooth)
Z= RPM, the speed at which the cutter revolves in the spindle. (Revolutions per minute)
We will now break down the relationship between the Feed rates, number of cutting edges, chip load and RPM. For most materials there is a recommended chip load.
If you are running at 18000 RPM using a 25mm cutter with two flutes, and a recommended chip load of 0.1 mm/tooth:
Feed = 2 x 0.1 x 18000 = 3600 mm per min
If the RPM were increased to 24000 RPM the new feed rate would work out to be:
Feed = 2 x 0.1 x 24000 = 4800 mm per min
Based on this equation, as RPM increases, feed rate will also increase if all other settings remain the same. If the number of cutting edges changes, however the feed rate will either increase or decrease depending on the whether the number goes up or down. The same applies to chip load if the recommended chip load is 0.1 mm/tooth the RPM, feed or number of cutting edges may go up or down to maintain the required chip load. Therefore if chip load remains the same, and feed rate increases, either the RPM and or number of cutting edges must increase to maintain the recommended chip load.
When calculating the feed rate for any material the chip load is therefore one of the most important factors to be taken into account because the chip load determines the amount of material that each tooth will remove, plus the load that each tooth will have to take. Another factor that affects chip load is the diameter of the cutter. A larger cutter will be able to handle a larger chip load.

No of cutting edges (Z)	Chip Thickness (mm)	Feed rate (mm/min) at RPM
		18000	21000	24000
1	0.1	1800	2100	2400
2	0.1	3600	4200	4800
3	0.1	5400	6300	7200
1	0.4	7200	8400	9600
2	0.4	14400	16800	19200
3	0.4	21600	25200	28800

Therefore depending on the diameter of the tool, if the RPM and number of cutter edges stay the same chip load will increase with a larger diameter cutter, thus the feed rate will also increase. When machining softer materials or using a stubby router bit the chip load can be increased. If an extra long router bit is being used, the chip load should be decreased.
For most material that you will be cutting on a CNC router you will typically set the RPM between 12000 and 24000, and adjust your feed rate to obtain the required results. The speeds and feeds chosen can be affected by the power of the spindle being used. Higher power spindles will produce more torque thus allowing the machine to run at a variety of RPM’s (torque drops off as the RPM is reduced).

Typical chip thickness values for various size cutters
Cutter Diameter	Hardwood	Softwood/Ply	MDF/Particleboard	Soft Plastic	Hard Plastic	Aluminium
3mm	.08 -.13	.1 - .15	.1 - .18	.1 - .15	.15 - .2	.05 - .1
6mm	.23 - .28	.28 - .33	.33 - .41	.2 - .3	.25 - .3	.08 - .15
10mm	.38 - .46	.43 - .51	.51 - .58	.2 - .3	.25 - .3	.1 - .2
12mm and over	.48 - .53	.53 - .58	.64 - .69	.25 - .36	.3 - .41	.2 - .25

Even though there are formulas for calculating feed rates you will find that optimum feed rate will be determined from experience. You will typically start off with the calculated feed rate. Under ideal conditions it is usually suggested that the actual feed rate be set to approximately one-half the calculated amount and gradually increased to the capacity of the machine and the finish desired.
Once you have determined what feed and speed to start with, there are other factors to be taken into consideration. The next thing to be considered is the direction of cut, which is the direction the cutter is fed into the material. Conventional milling or cutting forward is the most commonly used method. With this method the work is fed against the rotation direction of the cutter. The other method is climb milling or cutting reverse. For this machining method the workpiece and the machine must be rigid. When machining non-ferrous materials, climb milling should be used to achieve a good finish.
Another factor is depth of cut. Depth of cut will effect edge finish as well as tool life. You will have to adjust your depth to achieve the desired results depending on the type of material and size of cutter. Usually a depth of cut that equals the radius of the cutter is a good starting point when cutting non-ferrous metals.

The Do’s and Don’ts

Do …

Cnc Router Feeds And Speeds For Cutting 2.5mm Thick Aluminum Pipe

- Make sure you have the right router bit for the material to be processed

- Look up recommended settings when programming for a new type of material of router bit

- Check with your machine supplier if you aren’t achieving the expected quality or productivity

- Make sure your collet is not worn and the tool is fitted correctly

- Start with lower feed and plunge rates if not sure to avoid potential tool breakage or machine damage

Don’t …

Cnc Router Feeds And Speeds For Cutting 2.5mm Thick Aluminum Steel

- Forget that doing some test cuts on a spare piece of material is a good way of checking settings before running your main program
- Use worn or damage router bits which can cause overheating and poor cut quality
- Continue cutting if you hear an unusual cutting noise.
- Pause the machine and check the router bit and settings
- Cut too deep in a single pass. Sometimes it can be more efficient to use a higher feed rate and two or more passes rather than a single cut at a low feed rate