How To Use A CNC Router To Cut Aluminium ? | TheEdgeCutter

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People, especially beginners, often have queries regarding Aluminium and CNC routers asking if they can cut an Aluminum piece with their CNC router. As a router is generally used for slicing wood and plastic materials, my answer to the above query is "Yes, any CNC Router is fit for cutting Aluminium only if you can do that right.". 

So, what does that mean? Well, to do it right means you need to follow certain tips and guidelines while attempting to cut Aluminium on a router. Once you master a few points, you can easily and productively machine Aluminium materials with a router.

Just a little preparation and care, and you are all set to pursue the Aluminium cutting task. But, before I move straight to the tips of how you can use a CNC Router for Aluminum cutting, let's first understand what makes this task different from cutting a wooden or plastic material. 

How Aluminium is Different from Wood and Plastic? 

Firstly, the optimal speeds and feed rates range for Aluminium is quite limited. So, if you try to surpass that level, the cutter may end up breaking. Also, sometimes a lower feed rate can wear out the cutting bit a lot faster, affecting the tool life. As a result, you will get a poor cutting finish. 

Secondly, Aluminium has a stickiness factor, that is, its chip has the tendency to weld and stick to the cutter, which may jam the cutter flutes, causing the tool to break. Once the cutter gets gummy Aluminium chips deposited on it, that tool is no more useful for further cutting works, especially not for a speed that is 20,000 RPM or more.

Despite these issues and many others, you can still cut Aluminum quite conveniently with almost any router by applying these 11 tried and test tips

TIP No. 1 : Don't Work Hastily

You can cut Aluminum on a CNC Router, as long as you do the work with care and patience. But, considering the overall  Removal Rate of the material, CNC mill is way better and purposely built for Aluminum cutting. Conversely, sometimes even a big-sized industrial CNC router outranks a CNC mill and stands fit to allow a larger material cutting area on its table than most mills could. Simply, install the accurate bit, place the Aluminum piece on the cutting table, hit the green button, and relax.

TIP No. 2 : Get a Feeds and Speeds Calculator

To check the feed and speed limits of your CNC machine while cutting different sorts of workpiece, you will need a measuring device to give you an idea of how much speed or feed rate you should apply to the cutter. That's why you should use a feeds and speeds calculator. G-Wizard is one of the leading digital calculators used for this task. 

Cutting Aluminum with a CNC Router is not an easy task. So, you must be very digilent while cutting the material. For that, having a Feeds and Speeds calculator is really important.  If you ask any professional CNC-er, the first name he/she might recommend you is the   G-Wizard Feeds and Speeds Calculator. Well, there are many other choices on the market, but the one I just mentioned is typically designed to meet the CNC router's cutter feed rate and speed requirements. 

If you decide to go for a different calculator for your CNC machine, then make sure to check on the following points in that calculator:

  • Minimum RPM value: The calculator is not helpful if it only tells you to slow down the feed rate than you literally can. 
  • CNC Router Bit Types: Downcut bits, Compression bits, and V-Bits are the three most significantly used CNC Router bits. Check if your chosen calculator handles these end mills just like the G-Wizard does. However, these bits are not for Aluminium cutting (in case you want to try one).
  • Deflection: Tool deflection accounts for an increased tendency of tool breakage, and this is very common with any machining tool. So, make sure to use a calculator that presumes such risks of deflection beforehand and has other capabilities like CADCAM Wizards and Cut Optimizer to find solutions that prevent uncontrolled tooling deflection.
  • Rubbing Warning: Reduced fee rate will slow down the cutter resulting in unclear cutting finish on the Aluminium material surface. This faulty effect is called "rubbing" and it shortens the tool life affected by the heat generated by the cutter. So, make sure your calculator has a rubbing warning determiner.
  • Chip Thinning: You get thin chips when the cut width is less than half of the cutter diameter. However, with a proper calculator, you can compensate for thin chip cutting so that you don't end up damaging the cutting bits prematurely.
  • Derate Horsepower: Make sure the calculator features both full rated and derated machine profiles. This will help you to conveniently switch between a derated and full rating as per the material's cutting requirement.

The primary issue that you will deal with after getting a calculator is that the suggested value of RPM is lower than it practically can be done. For most CNC routers, the spindle speed is way faster than the CNC mills. Where an averagely new CNC mill features a maximum turning speed of 10,000 RPM, most CNC routers can not run that slow. For them, the speed begins at about 20,000 RPM (approximately).  The further set of tips typically focus on the solutions of this problem.

TIP No. 3 : Use CNC Router Carbide Bits to Cut Aluminium 

CNC Routers employ cutters of various sorts which may or may not be suitable for Aluminium cutting. For example, Compression bits, Downcut Spirals, and other like ones have no utility in Aluminium cutting.

2 to 3 flute Carbide Spirals are widely used  by the CNC routers for cutting Aluminium.  

This helps your machine reach the recommended higher RPM at which the router spindle operates. The measurement that calculates this parameter is called the Surface Speed. As I mentioned already, Carbide cutters are the best fit for Aluminium. This is because of their faster rotating speed compared to High-Speed Steel(HSS) bits. Even the Cobalt cutters are not appropriate for cutting Aluminum.

Let's suppose, you want to cut an Aluminium slot using a ¼ inch bit and you use a G-Wizard calculator for determining measurements. Now, if you pick an HSS type cutter, G-Wizard will recommend you to apply an RPM of 5877, while your router whose spindle speed is around 20,000 RPM can not go that slower.   So, in that case, you have to use a Carbide end mill. Now, the calculator will suggest a speed limit of around 17419 RPM, which is a closer value to the spindle's 20,000 RPM  value. Also, the Surface Speed this time is much higher with 1140 SFM(Surface Feet Per Minute). So, now you are good to start the slotting operation.

TIP No. 4 : Use Cutters/End Mills of Smaller Diameter

One more way to shoot up the RPM is to employ small diameter end mills. Skip the ½ inch one and move to ¼ inch bit, or it is even better if you can use one that is far less.

Note: Since you are going for the smaller diameter bits, make sure that the tool is rigid enough, else it will start deflecting from the track. Use a Feeds and Speeds Calculator to prevent risks of tool deflection. I would suggest using a Carbide end mill as its rigidity is more than the HSS bits. So, the former is a favorable option.

TIP No. 5 : Pay Attention to Clearing the Chips

Aluminium has a close affinity to stick to the cutter. So, recutting chips may affect more cutting bits and this is the most common that frequently happens.

Pay a little attention to clearing out these chips with a tried and tested vacuum dust cleaning system. If you ask me, I would suggest an air blast attached to the router spindle and pointed directly to the portion where the cutter meets the Aluminium piece being cut. Holding a brush in hand or a vacuum nozzle thinking you can manage to keep the cutting area clean, would be a flop idea. 

TIP No. 6 : Check on the Slotting and Depth of Cut– these make chip clearing harder 

With a deeper cutting depth, closer to a slot, the end mill travels deeper inside. Consequently, the chips then produced are harder to clear off from the bottom of the drilled hole. 

So, you can either try using an internal coolant or make several passes to cut through the required depth and open up the superficial  depths to get better access.

Note: While working on an Aluminium piece or any material that has Aluminium to any of its surfaces, set the Aluminium side up while cutting. It keeps the Aluminium chip clear from the cutting bit as fast as possible.

TIP No. 7 : Apply Coolant or Mist for Lubrication 

A CNC router will require lubrication of flood coolant or mist for hassle-free, smooth Aluminium cutting. So, your next step is to apply a lubricant to generate minimal friction and heat, and keep the chips away from the cutting edges. Unless it is a thin an Aluminium sheet, you will require using a mister. It is quite affordable and easy to provide lubricating coolant and air blast to cut Aluminum plates (or other metals).

The best part of the mister is you can set how much fluid you want it to spray during the cut so that it doesn't make a mess around. Just make sure to set the mister spraying nozzle in a way that it directly sprays where the cutter meets the material cutting surface. 

TIP No. 8 : Do Not Decrease the Feed Rate Much 

Slowing down the feed rate can cause tool head rubbing due to which you may get a poorly cut finish on the material surface. This is a notable setback for the CNC router users compared to the mill users because the spindle speed in the former type is much faster. So, to keep things compatible, you have to maintain an optimal tool head RPM that smartly matches the router's spindle speed.

For example, you want a 3/16 inch cutter at 21,000 RPM to be fed at 91 IPM. But, if you reduce the rate to almost ¼ (say) of that, you are actually hampering the tool life causing it to get drastically rubbed at 20,000 RPM.

However, the good news is you can stay on top of this rubbing issue with a G-Wizard calculator that warns you about this problem much earlier.

TIP No. 9 : Use End Mills with Less Flutes for Faster Feed and Increased Depth of Cut

The CNC router cuts Aluminum the best with a 1 flute end mill. This way, the Aluminium chips don't get enough space to accumulate within the flute, which otherwise hampers the feed rate of the machine, thereby breaking the CNC bit.

Normally, it is suggested to use end mills that have less than 3 flutes. A 3 flute router bit is also workable in this regard; just be sure not to use bits with 4 or more flutes in Aluminium cutting.

Why? The more the flutes, the greater is the space for the larger Aluminium chips to get accumulated within. Conversely, fewer flutes gives more area of cutting and room for the chips to blow away. Too many flutes in CNC bits causes the chips to jam the flutes, which may ultimately break the cutter.

Let's consider a situation where you have a G-Wizard calculator that recommends you to use a 3 flute router bit at 166 IPM. But, your CNC machine can only support a speed of 100 IPM to cut the Aluminium piece accurately. So, what to do in such cases?

It's simple. You just have to replace the 3 flute with a 2 flute end mill to achieve the feed rate 110 IPM.

If you want to use a 1 flute end mill at an RPM of 20,000, and G-Wizard recommends a feed rate of 294 IPM.

TIP No. 10 : Use a Derated Horsepower Limit to Match the Router's Rigidity

Now that you have mastered the above 9 points and things are heading smoothly, you may be running against the machine's rigidity limits. So, if you ram in full power, things might get worse and the machine may chatter, destroying the cutter bit. As a result, you may either get a poorly finished Aluminium surface or the machine may deflect and deliver inaccurate cuts.

The force required to cut a metal piece is much higher than that required for wood cutting. The Gantry mills which we normally call CNC routers are comparatively less rigid than CNC mills, and are fit for cutting wooden materials. This is one point. Another is the work envelope of a CNC mill (lower than CNC router) and mill's weight (higher than a router) against a Gantry mill. An industrial Gantry mill is, however, an exception. Other than this a CNC machine is no way as rigid as a CNC mill. Except for the biggest industrial Gantry Mills, So, you need to compensate.

The exact rigidity value of the machine (CNC router) is not known as there is no published benchmark specification that I could use for comparing or calculating the rigidity parameter. However, as a substitute, I used the spindle power; a "pushing" force against the Aluminium workpiece during its cutting, which the machine's rigidity must withstand. G-Wizard is a popularly used machinist calculator that can calculate a "derated" spindle power value which is compatible with the weight and work envelope of your router and its rigidity level. The results may be surprising. They are, however, based on practically observed values.

Derating the Horsepower limit to 0.17 HP will take down the feeds and speeds down to 22K RPM and 79 IPM respectively, for a full slot with a 3/16 inch and a 2-flute end mill. But, you will get a better cutting accuracy, well-finished surface and little tendency to deflect the router alignment.

Note: Do not reduce the machine power frequently. Keep both derated and non-derared machine profiles and employ the derared one while expecting a finer cut finished surface or in cases when the cutter has the tendency to break.

TIP No. 11 : Cutting an Aluminium Sheet with a CNC Router is Different from Cutting Aluminium Plate with CNC Router

The thicker the Aluminium workpiece, the higher is the depth of cut. So, greater should be the spindle speed with an optimal feed rate such that the CNC cutter against the Aluminium doesn't break. Also, you must know that the RPM value will differ according to the diameter of the CNC bit used, ranging roughly within ⅛ to ⅕ inch bits. 


FAQs

Can I cut Aluminium using a CNC?

Yes, you can easily cut Aluminum using a CNC. Just make sure to choose the right bit or cutter and apply the correct speed and feed, to avoid the possible hazards explained in this article. 

What is the primary reason behind failed cutting of Aluminium with a CNC router? 

Lack of lubrication is the primary reason behind the failed Aluminum cut with a CNC Router. The chemical affinity of Aluminium causes its chips to stick to the cutter if proper lubrication is not included.

How to achieve a feasible CNC router speed and feed for cutting Aluminum?

Install a high quality speeds and feeds counter for CNC routers to help achieve a desired feed rate and speed for Aluminium cutting. Apart from that, many other typical issues relating to CNC routers must be taken into account to obtain proper feed rates and speeds.

Which CNC router bits are the best for cutting Aluminum?

Employ high quality Carbide based 3 flute or 2 flute end mills to get the best Aluminium cutting experience.


Conclusion

Using a CNC router to machine Aluminum is absolutely achievable. All you need to check on are the proper speeds and feed rates, installing proper bits that match the thickness, texture, and other cutting cum tooling parameters for the Aluminium material. I hope this article helps. I will get back with many other interesting posts regarding CNC routers. Stay tuned!

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