This is arguably the most important feature to consider when choosing an end mill for CNC machined aluminum. Again, aluminum is gummy and soft, which means it tends to stick in the flutes of your CNC mill. While coatings can help alleviate this issue, if you’re using a 4- or 5-flute end mill to cut aluminum, even the best coatings may not help. One of the main goals of flutes when cutting aluminum is to clear CNC machined chips. While having fewer flutes makes your tool less rigid, it also allows for more efficient movement of those chips. If you don’t get chips out of there, you risk ruining your surface finish, by re-cutting chips, or worse, destroying your end mill by friction welding the chips right to your cutter - every CNC machine owners worse nightmare! Your best bet for an end mill in aluminum is two or three flutes. While you can get away with more flutes, if you are really concerned about rigidity, your risk of destroying your end mill will go up.

Not at those prices I won't. 10 Euro's for one drill? I can get the microbox set I linked above for that, or a pack of 10 replacement bits.

It's not my only guide, but value for money wise most modellers don't need expensive high precision drills to drill holes in plastic models. The microbox drills and other like them are perfectly adequate for the job.

I got fed up breaking the cheapo drill bits but now I use Proxxon drill bits such as these Proxxon 28255 Diamond Twist Drill Bits 0.8 and 1.2 mm. Not cheap but worth it in the long run .

I've given up on buying drill sets, as like others I keep breaking the finer bits - or the carpet monster eats them. Instead I buy packets of 10 HSS bits off Amazon.

You're right, they are good, and also easy to change, as the base is thicker. I did something stupid and broke the 0.2mm, but 0.3mm is still going strong.

If you ask five CNC machinists the same question, you’re bound to get seven answers. But that doesn’t mean they're indecisive, just there are many different ways to perform any given CNC operation. That being said, there is no 100% right or wrong way to cut aluminum, but here are a few things to keep your eyes on when buying end mills.

I currently use PCB drills (bought off Ebay cheap) however, I find them incredibly brittle and the thread is very, very aggressive, which often means the drill bits bite and snap (especially in resin).

@Dave Swindell many thanks for the recommendation! I'd seen those at my local (Jadlam), will pick up a set next time I'm there

Aluminum makes lots of little flakes and shavings when it's milled. I used to work at a machine shop. I hated that stuff, too! It gets everywhere!

https://www.performacut.co.uk/hss-drill-bits/hss-jobber-drill-bits/phantom-psd-hss-jobber-drill-118-0-2mm-to-20mm-11450?returnurl=%2fsearch%3fq%3d0.3mm

Interrupted cuts are hard on tool life and surface finish, so using high-helix geometries allows you to stay more consistent and move CNC machine chips out faster. Interrupted cuts wreak havoc on your parts. This video shows how interrupted cuts with a chipped end mill can affect your cutting strategies.

I've given up on buying drill sets, as like others I keep breaking the finer bits - or the carpet monster eats them. Instead I buy packets of 10 HSS bits off Amazon.

https://www.performacut.co.uk/hss-drill-bits/hss-jobber-drill-bits/phantom-psd-hss-jobber-drill-118-0-2mm-to-20mm-11450?returnurl=%2fsearch%3fq%3d0.3mm

If you’re looking to cut aluminum, fear not… it’s a forgiving material. If you want to cut aluminum better, look for end mills with high lubricity and an efficient flute design for chip evacuation. With some fine-tuning in your feeds and speeds, you’ll use your CNC machine to make piles of aluminum chips in no time.

I think I've only ever broken the two smaller sizes in my set, and like you I've bought packets of 10 so as to have spares in stock. Shesto do the sets and packs of 10 individual sizes, so you have a choice of what suits you best. Personally, I like the set in the handy storage box, and I'd recommend it to anyone looking for a general purpose set of small drills, however I've only ever bought two sets, one for the home workshop and another for a travelling toolbox.

I currently use PCB drills (bought off Ebay cheap) however, I find them incredibly brittle and the thread is very, very aggressive, which often means the drill bits bite and snap (especially in resin).

So much of CNC machining is about math, and choosing an end mill is no different. While the number of flutes is an important consideration, flute geometry should also be considered. High-helix flutes help dramatically with CNC chip evacuation, and they also help with the cutting process. High-helix geometries have more consistent contact with your workpiece… meaning, the cutter is cutting with fewer interruptions.

Surprised no one has mentioned the Tamiya bits? For small sizes I find them great as they have really accurate but short threads and sturdy shank. The cutting portion is only 4 or 5mm long so difficult to break and while I’ve gone through boxes of pcb bits (and still find them good for bits about 1mm and up ) I now have the full set of Tamiya bits from 0.2mm to 1mm. Not cheap but never had to replace any so actually good value. Also don’t have to try and dig broken pcb bits out of my models

I remember talking to my dad about small drill bits. He worked in light engineering all his life and must have drilled millions of holes. Small drill bits in metal didn't last long for all sorts of reason, but largely because they were so small and relatively fragile despite whatever they were made out off. He reckoned that the really small bits in plastic suffered because plastics are relatively good insulators of heat, and so the area around the bit heats up. In some cases the plastic will soften and foul the bit, thus making it more likely to break. Also plastics may not be a consistent density. A

Not at those prices I won't. 10 Euro's for one drill? I can get the microbox set I linked above for that, or a pack of 10 replacement bits.

Aluminum is soft when compared to other metals. This means chips can clog up the flutes of your CNC tooling, especially with deep or plunging cuts. Coatings for end mills can help alleviate the challenges that sticky aluminum can create. Titanium carbo-nitride coatings are slippery enough to help keep chips moving, especially if you aren’t using coolant. This coating is often used on carbide tooling. If you’re using high-speed steel (HSS) tooling, look for coatings like titanium carbo-nitride (TiCN). That way you get the lubricity needed for aluminum, but you can spend a little less cash than on carbide.

Surprised no one has mentioned the Tamiya bits? For small sizes I find them great as they have really accurate but short threads and sturdy shank. The cutting portion is only 4 or 5mm long so difficult to break and while I’ve gone through boxes of pcb bits (and still find them good for bits about 1mm and up ) I now have the full set of Tamiya bits from 0.2mm to 1mm. Not cheap but never had to replace any so actually good value. Also don’t have to try and dig broken pcb bits out of my models

lot of industrial cutting and drilling uses/used cutting oils or other lubricants to ease the process, and also cool the work piece I have long since accepted that small 0.3mm/80 drill bits will not survive long.

Going on from above. A good lubricant for cutting plastic is water believe it or not. However the sort of drilling we do in plastic is more of a case that the drill bit is rotated by hand rather by machine. so heat should be minimal.

I have been modelling for years and constantly have to keep buying new drills......only break .5 and below - all the time(at least 30 years plus).  I have tried all makes of drills, diamond, etc, you mention it, I have used/tried it......anything below .5 is going to eventually break, if it doesnt, it either goes blunt or bent........impossible to see the tips to resharpen, even purchased jewelry drills.....tried everything.  You just have to accept, those small drills have a limited shelf life........I just write off to various Jewelry  shops and buy bulk drills.....10 x .5   - 10 x .4 -   10 x .3................have many duplicates now of the sizes that do not break......being so fine, they are a welcome prize for the carpet monster......I have a special mains miniature vacu-cleaner, just to hoover the carpet about once per month.

I have used two sets from Trumpeter Master Tools for several years, #09954 and #09955. I have managed to break only the 0.3mm, wasn't careful enough. I don't drill resin, just polystyrene which is softer, so I don't how long lasting they would be if used to drill resin parts.

Carbide stays sharper longer. While it might be more brittle than other end mills, we’re talking aluminum here, so carbide is great. The biggest downside to this type of end mill for your CNC is that they can get pricey. Or at least more expensive than high-speed steel. As long as you have your speeds and feeds dialed in, carbide end mills will not only cut through aluminum like butter, but they will also last quite a while. Get your hands on some carbide end mills here.

Sadly, those PCB drills are not at all suitable to hand drill as they're far too brittle. I had a set and they snapped with the least bending. I stick with regular HSS sets.

Someone on the RPF forum puts the insulation from electrical wire around the shank of their micro drill bits. The effect is some slight give in the shank where it's held in the chuck/collet and where it tends to snap, and not one has broken since he started doing it.