Since When Were End Mills So Interesting? (+8 Bonus Tips)

Posted By: TYLER WELCH

Published: 18/08/2021

End Mills are a type of milling cutter and are essential for the cutting performance of a milling machine. According to a recent data report by 'Strategyr' the milling machine market is expected to grow massively in the coming years, and end milling is one of the most common procedures in industrial machining and applications. Read this article to learn everything there is to know about End Mills.

What Makes An End Mill Different?

People unfamiliar with cutting blades might be slightly confused about the difference between end mills and drill bits. It’s fairly simple: the main difference becomes clear when you take a closer look at the shape and geometry of the bits and its flutes.

This process differs from other operations due to the cutting teeth on the sides and end of the mill, the main difference compared to other cutters like drill bits. A drill bit is designed to cut (drill) directly into the material and create holes in the axial direction only. End mills can cut laterally into the material and create slots or profiles. Some types even cut in all directions and are therefore more flexible allowing for profile, tracer or face milling, plunging, contouring, slotting, drilling, and reaming operations.

To break it down:

End Mills

1. End Mills cut rotationally in a horizontal, or lateral (side to side) direction whereas a drill bit only cuts straight down, vertically into the material.

2. End mills are available in a wide variety of lengths, diameters, flutes and types, and are chosen according to the material they are cutting and the surface finish required for the project.

3. End mills are the cutters of the milling world and are used for slotting, profiling, contouring, counter-boring, and reaming.

4. End mills allow for precision parts to be cut, anything from machine parts, jewellery designs, wood engravings, sign making, plastic cutting, mold making and circuit boards.

 

Drill Bits

1. Drill Bits cut round holes straight down into the material by rotating them in a rotary drill.

2. Most drill bits have a spiral groove (flutes) which give the drill bits a twisted appearance and helps to cut away material as they move up and down in the hole.

3. HSS (High Speed Steel) and carbide drill bits are fluted. (twist drills)

4. The exception to this rule are diamond drill bits which have a flat end rather than pointed or fluted. (Unless it is a diamond twist drill which is not used for drilling but for expanding already existing holes such as in beads)

The Anatomy Of An End Mill

End mills feature many different dimensions that can be listed in a tool description. It is important to understand how each dimension can impact tool selection, and how even small choices can make all the difference when the tool is in motion.

VOR65-B2

Profiles 

The profile refers to the shape of the cutting end of the tool. It is typically one of three options: square, corner radius, and ball.

Square Profile End Mills - Square profile tooling features flutes with sharp corners that are squared off at a 90° angle.

Corner Radius End Mills - This type of tooling breaks up a sharp corner with a radius form. This rounding helps distribute cutting forces more evenly across the corner, helping to prevent wear or chipping while prolonging functional tool life. A tool with larger radii can also be referred to as “ball nose.”

Ball Profile End Mills - This type of tooling features flutes with no flat bottom, rounded off at the end creating a “ball nose” at the tip of the tool.

VOR55-S2 DIMS

Cutter Diameter (D)

The cutter diameter is often the first thing machinists look for when choosing a tool for their job. This dimension refers to the diameter of the theoretical circle formed by the cutting edges as the tool rotates.

 

Shank Diameter (D2)

The shank diameter is the width of the shank – the non-cutting end of the tool that is held by the tool holder. This measurement is important to note when choosing a tool to ensure that the shank is the correct size for the holder being used. Shank diameters require tight tolerances and concentricity in order to fit properly into any holder.

 

Overall Length (L2)

Overall length is easy to decipher, as it is simply the measurement between the two axial ends of the tool. This differs from the length of cut (LOC), which is a measurement of the functional cutting depth in the axial direction and does not include other parts of the tool, such as its shank.

 

Flute Length (L1)

An end mill’s flute length, is simply the length of the cutting part of the tool. It is measured from the start of the necked portion to the bottom of the cutting end of the tool.  The neck relief allows space for chip evacuation and prevents the shank from rubbing in deep-pocket milling applications. 

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Helix Angle

The helix angle of a tool is measured by the angle formed between the centre-line of the tool and a straight line tangent along the cutting edge. A higher helix angle used for finishing (45°, for example) wraps around the tool faster and makes for a more aggressive cut. A lower helix angle (35°) wraps slower and would have a stronger cutting edge, optimized for the toughest roughing applications.
A moderate helix angle of 40° would result in a tool able to perform basic roughing, slotting, and finishing operations with good results. Implementing a helix angle that varies slightly between flutes is a technique used to combat chatter in some high-performance tooling. A variable helix creates irregular timing between cuts, and can dampen reverberations that could otherwise lead to chatter.

VOR45-KM

Flutes

Flutes are the easiest part of the end mill to recognise. These are the deep spiralled grooves in the tool that allow for chip formation and evacuation. Simply put, flutes are the part of the anatomy that allows the end mill to cut on its edge.

One consideration that must be made during tool selection is flute count, something we have previously covered in depth. Generally, the lower the flute count, the larger the flute valley – the empty space between cutting edges. This void affects tool strength, but also allows for larger chips with heavier depths of cut, ideal for soft or gummy materials like aluminium. When machining harder materials such as steel, tool strength becomes a larger factor, and higher flute counts are often used.

What's the Difference Between High Speed Steel (HSS), Powder Metal & Carbide?

HSS

HSS is known for its ability to withstand high temperatures while maintaining its hardness. While HSS suffers from much slower cutting speeds than carbide, it is less prone to drill breakage and can perform well for a considerable length of time. HSS has proven cheaper and more effective in use with multi-toothed form cutters, with re-sharpening after a lengthy duration of use a snap. HSS is very forgiving, it will not just chip or fracture easily.

HSS end mills find regular use in drilling small diameters or large depths, where the material’s strength at withstanding cutting force makes it an asset despite natural limitations in cutting speed. HSS can also be used for milling cutters, tool bits, saw blades, and other cutting tools used for low-speed applications, where its high hardness can be best put to use.

 

Powder Metal

Powder metal is simply the medium between HSS and Carbide, it has the toughness of HSS with the tool life and wear resistance of carbide. It is perfect for high performance machining where vibration will be an issue. Because of this, it is a great choice for machinists wanting to upgrade from HSS. 

Powder metal cutters can be used on both manual and CNC machines and are also excellent for machining stainless steels.

 

Carbide

Carbide tooling comes with high efficiency in use and retains its cutting edge well at high machining temperatures. Compared to HSS, carbide tools boast a higher cutting speed range and improved rigidity. Carbide tools are known to provide exceptional surface finish quality.

Due to these advantages, carbide finds use in most cutting applications, from boring to face milling and beyond. Carbide is often used when machining on cast iron, plastics, and other nonferrous materials.

 

8 Common Problems With End Mills And Their Solutions

 

Tip #1: End Mill Breakage

There are several common causes of end mill breakage. Your feed could be too heavy. Check it and reduce the feed rate if it’s obvious the machine is biting off more than it can chew. The cut programmed into the machine could also be too aggressive; try decreasing the width and depth of your cut to fix this issue. 

There could also be too much tool overhang, meaning you’d need to hold the shank deeper or use a shorter end mill for your work. And lastly, the cause could be simple wear and tear. If your carbide cutting tool is too dull, it’ll break. Make sure you check it consistently and sharpen it before it becomes too worn down.

Tip #2: Unusual End Mill Wear

Check the following simple things to see which one of them can cause unusual wear on end mills:

  • Speed and rates could be too high. If so, adjust them accordingly.
  • If the material you’re cutting is too hard, make sure you’re using a coating like TiAlN or AlCrN.
  • Incorrect helix angle can cause unusual wear, so check to make sure it’s right if you notice this.
  • The primary relief angle could be too large. Decrease it to correct the problem.
  • When re-cutting, chips of material can get in the way and cause wear. If you notice that happening, try adjusting the speed, feed, and chip size. You can also clear chips with more coolant and air pressure.

Tip #3: Short Tool Life

If your metalworking equipment is wearing out faster than it should, one of the following could be the culprit:

  • The cutting friction is set too high.
  • Cutting hard material without coating.
  • Incorrectly set helix and relief angles.

Make sure your tools are sharpened, you’re using the proper coating on hard materials, and that your angles are correct. 

Tip #4: End Mill Chipping

Heavy feed rate and lack of rigidity can both cause chipping. Make sure you reduce the feed rate if you suspect a problem. You can also try using a shorter tool, holding the shank deeper, or climb milling. 

Tip #5: Excess Chip Packing

Check for the following problems if you experience excess chip packing: 

  • The cut is too heavy.
  • Not enough chip clearance.
  • Insufficient coolant.

You can try and correct this problem by decreasing the width and depth of your cut, using an end mill with fewer flutes (for chip clearance), or using higher coolant pressure and directing the coolant nozzle at the point of cut. Air pressure can also be used. 

Tip #6: Burrs

If you’re getting burrs, check to make sure your tool is sharpened, that your feed and speed rates are correct, and that your helix angle is set properly. 

Tip #7: Rough Surface Finish

Be on the lookout for any of these factors that can cause a rough surface finish:

  • The feed rate is too heavy.
  • Slow cutting speed.
  • Worn tools.
  • Shallow dish angle on the end of your tool.

If your product has a rough finish, try correcting the feed rate and speed, swapping out a dull tool for a sharp one, or increasing the dish angle on your tool. 

Tip #8: Chattering

Chatter can be caused by:

  • Feed and speed being too fast.
  • Lack of rigidity in your setup.
  • Poor setup in general.
  • The cut is too heavy.
  • Too much tool overhang.

Correct for this by making sure your feed and speed settings are correct, improving clamp rigidity, or decreasing the width and depth of your cut. You can also try using a shorter tool, climb milling, or holding the shank deeper. 

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