This is a short overview of mill cutting tools. Check the suppliers page for tooling suppliers.

General properties

Material

First off, machine tooling comes in two main types: high speed steel (often abbreviated to "HSS") and Tungsten carbide (often displayed as just "carbide"). HSS tooling is much softer than carbide, meaning that the edges wear more quickly and a long HSS tool has a tendency to vibrate in the cut, leading to chatter. Carbide is more expensive than HSS and is more likely to come coated. End mills are typically carbide and benefit significantly from the rigidity it provides. Drills and other holemaking tools on the other hand are typically HSS, steel's flexibility prevents the drill from breaking as it enters the cut, and the hole reinforces the tool, preventing chatter.

You can identify if a tool is HSS or carbide by weight. Carbide is around 2x as dense as steel, so the difference in weight will quickly become obvious.

Importantly, do not put carbide in a mill drill chuck (even a carbide drill), it will prematurely wear out the jaws.

Flute count

Flutes are the cutting edges of a tool. A typical twist drill has 2 flutes, while mills commonly have 2 to 6, though specialty ones can have far more. Flute count determines how fast you can move through material, with more flutes typically being faster than fewer flutes.

But as you increase the number of flutes, you reduce the space for a chip to form between them. If you're cutting soft material like copper or aluminum quickly or without coolant this space can fill up, often causing the tool to snap.

More info available here

Coating

Cutting tools are frequently coated with a material harder than carbide to extend tool life even further. Sometimes it's literally diamond. These coatings occasionally react poorly with some materials, so it's important to either know what material you'll be using or getting a general purpose coating. There are a whole ton of coatings, some are proprietary, so I'll only go over a couple here.

• TiAlN or AlTiN: Titanium Aluminum Nitride is a very tough coating, very good for cutting steel and stainless. But because it contains aluminum, aluminum sticks to it, for this reason you want to avoid AlTiN coated tools while cutting aluminum.
• DLC: Diamond-Like Carbon, it's very close to as hard as diamond, but it has the unfortunate property of burning and dissolving in steel under the temperatures and pressures in the cut. This makes it unsuitable for cutting stainless and steel, or cutting very hard metals. But it'll last pretty much forever in aluminum.
• Uncoated or bright finish: As the name suggests, this is just uncoated carbide. Without the coating, these tools are sharper than coated tools, and they give a good finish, but tend to chip after significant use. I'd recommend them if you want a tool that's dedicated to finishing parts.
  

Tool types

There are numerous types of milling tools out there, some are versatile and cheap, others are quite expensive but may be necessary for certain things.

End mills

These are the most common and versatile type of milling tool, with cutting edges on the sides and bottom. They are capable of taking side cuts and doing most basic machining operations.  In the manual, they can make slots, shallow holes, and finish walls and floors. In the Tormach, they can also do helical boring, making them a replacement for a reamer for most situations.

Bull nosing is a usually small radius (0.005-0.015) ground onto the corner of the end mill. This is useful to prevent tool wear, as it's usually the corner that chips first. I would recommend it for a tool that will be cutting harder metals, but be aware of the inside corner if you have a mating part. 

Chamfer mills

Chamfer mills are also designed to side mill (as opposed to drills, which plunge into material). They're similar to end mills but with much less flute and a 90 degree included angle, so they make a sloped surface. They are used to create very small chamfers on parts to break sharp edges and make a professional appearance, or a large functional chamfer if necessary.

Drills

The second most common tool type. Machinists typically use twist drills that look very similar to the common ones you're familiar with. In a pinch, a hardware store twist drill will typically do the job for a short time, but a drill from a metalworking supplier will usually be much harder and last longer.

Drills are often labeled as "cobalt," which is short for cobalt steel. It is a very good tool steel for metalworking drills, and usually the price difference between a cobalt vs HSS drill is small, and I would recommend getting cobalt.

Drills come in a wide variety of lengths.

• Stub length drills are around 5x diameter, making them much stouter and cheaper. If you're starting on an uneven surface and haven't spotted the hole, use a stub drill.
• Jobber drills are considered the basic length, and have a flute length of around 10x their diameter. It's a good, versatile length that often comes in a drill index.
• Taper drills are long, around 15x diameter. They are quite spindly. Avoid these unless you need them, and if you do need to drill that deep, you'll need some extra precautions with your start and to evacuate chips.
• Aircraft length drills are exceptionally long, usually 6in regardless of diameter. They should be avoided.
  

Drills come in a frankly ridiculous system of diameters: Letter size, fractional size and number size for Imperial measurements. If you're working in metric, you'll just have mm diameters.

The [tap & drill diameter chart](https://www.brokenbolt.com/images/starrett-inch-metric-tap-drill.pdf) is pretty critical for selecting the right drill diameter, especially if you're tapping a hole. You can deviate from the recommended size a little, but that's outside the scope of this topic.

A drill index is just a collection of different-size drills -- usually fraction sizes. A good quality one can be pricey, but it would be worthwhile to have your own, so that you can guarantee you have basic drill sizes.

Taps

Taps are there just to make threads from an already-drilled hole. These do not get chucked into the machine directly, and instead you need a tap handle to drive them. Do not attempt to power tap with either the Tormach or the manual, it will not end well. Instead, use the Lab's spring-loaded tap guide and a tap handle to get a good start.

Taps are sensitive to their pre-drill hole diameter. You'll need to be close to the recommended pre-drill size for things to work. Refer to the [tap & drill diameter chart](https://www.brokenbolt.com/images/starrett-inch-metric-tap-drill.pdf).

Spot drills, Center drills and Countersinks

A spot drill is just a very stout drill that will make a small spot for a longer drill to use to get a good start. This helps position your hole precisely, and are recommended for all drills, and required if you're using a taper length or longer drill.

A countersink is used to apply a chamfer to a drilled hole. This can be done for either cosmetic reasons, to deburr a tapped hole, or to accept a countersunk screw. If it's the latter, be aware that inch uses a 90 degree countersink, while imperial uses an 82 degree countersink.

A center drill is technically a drill designed to place a lathe center. But they are cheap and because their geometry includes a taper, they can also be used as a countersink though the angle will not be appropriate to accept a countersunk screw.

Reamers

Reamers are another tool used to finish a hole. They are designed to remove only around 0.005 of material off the diameter of the hole, chasing it out and bringing it to a precise size. They are the most common way to create a precision hole in a manual machine. In the Tormach, helical boring can do the same thing, but a reamer might be necessary if you intend on making a very deep precision hole.

Be aware that reamers follow the drilled hole location, if the hole is off center or crooked, the hole will still be crooked after a reaming operation.

Broaches

Broaches don't spin, they instead plunge through the material and scrape off a chip in many passes, with the help of many cutting flutes. Currently, the makerlab does not have the equipment to support broaching. We need an arbor press to support this operation.