Chapter 9 Part 3: Manual Vertical Milling Machines

TOOL HOLDING

Tool holding devices on a milling machine are designed to securely hold the tools for various operations. They need to be simple, quick, and easy to use. The most common tool holding solutions on milling machines are drill chucks and collets. These solutions come in many different styles, but they all perform the same function of holding the tools. It is very important to point out that drill chucks are only used to hold the hole making tools outlined in the drill press chapter. Tools that cut in a lateral motion require more support than a drill chuck can provide.

End mill holder

An end mill holder is a solid R8 tapered holder that has a set screw for securing an end mill or other side cutting tool. In addition to the precision taper, there is also a precision diameter. Both of these mate up against or inside the precisely ground spindle. The holder also has a thread in the end to tighten the tool into the spindle.

Spring collet

A spring collet, often just called a collet, also has an R8 taper, a precision diameter, and a thread in the end. However, these holders are not solid; they are flexible. The collets use this flexibility to clamp onto the tool as the drawbar pulls the collet up into the taper of the spindle. Collets are not designed to grip on diameters larger or smaller than the advertised size. Doing so could damage the tooling, the collet, or allow the cutting tool to slip during the machining process.

Draw bar

A draw bar is a long rod that has a head with a hex on one end and threads on the other. The draw bar sits inside the spindle, and the larger diameter head rests against the top. The threaded end of the draw bar is used to screw into the ends of various tool holders that may be inserted into the spindle. As the draw bar is tightened, the tool holder gets pulled further into the spindle and increases the engagement of the R8 taper, locking it in position.

Drill chuck

A drill chuck for milling machines can be similar to those of the drill press but is often of better quality and may be of the keyless variety. Keyless chucks have a couple advantages over keyed chucks. The first is that they are easy to use and require only hand strength to tighten. The second is that if they start to slip, the internal mechanism will twist, tightening the chuck and stopping the slipping action. One thing to note, is that drill chucks are only for holding plunging style tools that are capable of stabilizing themselves. End mills and all other side cutting tools can not be held securely in a drill chuck.

TOOLING

Tooling is a term used to talk about the tools used on machinery to cut the parts. On milling machines, the tooling might look similar to that of a drill press; however, aside from hole making tooling, the tooling designed for a milling machine is very different. Specifically speaking, milling machine tooling is designed to cut horizontally. Because of the capability of the milling machine to facilitate sideways cutting, the machinist can create flat, straight sides and rectangular parts. The tooling for a milling machine consists of a variety of different designs that allow the machinist to create different shapes for the features that may be required of a part.

Tooling materials

Tooling for milling machines can be made of a number of different materials. High Speed Steel (HSS) is often considered the baseline material for tooling in a machine shop and is often used on manual milling machines because it makes a great economical material for end mills and other rotary tooling. Generally, machine tools for cutting metal will never be of a quality less than HSS; however, there are many materials that have properties greater than HSS that are occasionally used on manual milling machines (Beaumont, n.d.). Cobalt tooling has a higher percentage of cobalt in its alloy than regular HSS. It can be used effectively to machine harder alloy steels and stainless steel. Carbide is another very popular tool material for its additional rigidity and heat resistance. In addition to base materials, coatings on tooling are a huge part of selecting a tool. Some tools are also made with an alloy steel body and indexable insert cutting edges. This design makes these tools more economical than a solid carbide tool.

Face mill

A modern day face mill has many indexable carbide inserts that are designed to cut the top of the work. This cutting action is called facing. Face mills can be as small as 1” in diameter to as big as 10”or larger. For manual equipment, 1”- 3” face mills will be the most common. It is advised to use face mills with a high positive rake because of the relatively low horsepower of many vertical manual milling machines. Neutral or negative rake facemills or facemills over 3” are only recommended for use on larger, more powerful, machines. For facing cuts over 3” in diameter, a fly cutter would be a better tool than a face mill.

End mill

An end mill, despite its name, does a majority of the cutting on the side of the tool. At first glance, the end mill looks similar to the twist drill, but that is where the similarities end. Some end mills are referred to as “center cutting” and are capable of plunge milling with the end of the tool, but this isn’t the tool’s main function. On a milling machine, end mills do a majority of the shaping of parts. From contours and angles to slots, grooves, and bosses, end mills are a very versatile tool. End mills come in a few different styles, rougher, finishing, inserted, ball nose, bull nose, 2 flutes to 6 flutes or more. Generally speaking, for a heavier cutting operation or sticky material, an end mill with fewer flutes works better because it allows the chips to flow freely through the flutes and not build up. For a finishing operation, or in harder materials, an end mill with more flutes can be used because it will remove less material and require less chip clearance. For manual milling machines, ⅛” to ¾” end mills are common. Anything over ¾” is not recommended because it often requires more power and rigidity.

Boring head

A boring head is a tool used on a milling machine for the purpose of boring holes to size with an attached boring bar. The boring head operates by spinning the offset boring bar in a circle around the center of the spindle. The bottom half of the boring head can accommodate the boring bar in three different positions, two facing down and one facing out. From these three different positions, the boring head is capable of boring a wide range of sizes. The boring head is adjusted by a screw mechanism in the main body, and the lower half moves on a dovetail. This screw mechanism has graduations of .001”. Boring heads come in many different sizes, with, 2” being a common size for a manual milling machine.

Slitting Saw

A slitting saw is a tool that is used to cut thin sections of material from a part using a horizontally rotating saw blade. The blade is held on an arbor and is secured by a key and a compression cap. Smaller saws may just utilize the clamping force of the cap to hold the saw in place. Slitting saw blades can be HSS, carbide, or carbide inserted to name a few. On manual equipment, generally HSS saws under 6” in diameter are used.

Form tool

A form tool is a specialty tool that has the exact shape needed on the part, already formed into the shape of the tool. This allows for a single pass to create critical and difficult to machine features in most instances. Some examples of standard form tools would be radius tools, woodruff key cutters, tee slot cutters, and dovetail cutters. Custom form tools can be any shape the tool maker can think of to create to make the production of a part easier. Think of door and window molding used in a home. Most moldings have a slightly different shape. Each different shape has a different router bit profile to create it. This same concept is used on custom form tools for milling machines.

Hole-making tools

Hole-making tools, such as drills, reamers, taps, countersinks, and counterbores, previously discussed in the drill press chapter, are also utilized on the milling machine.

TOOL SETUP

Setting up tooling on a milling machine requires some calculation, checks, and adjustments to make sure the cutting process will be successful. A couple of the most important things to think of when setting up tooling on a milling machine is to use the correct tool for the cut and to keep the tool setup as rigid as possible.

When selecting tools, a good rule to follow is to use the largest diameter and shortest tool that will be able to complete the job. Keep in mind that end mills are the most common cutting tool and generally come in sizes from ⅛” to ¾” for manual milling. If the print requires a deep cut with a lot of metal removal, a larger diameter tool will be more rigid and remove the material faster than a smaller diameter tool. If the print requires a narrow, shallow cut, a shorter tool would be better suited for the cut than a long tool because it will be more rigid and cut more accurately with fewer issues.

When loading the tool, the operator must think of how to optimize the rigidity of the tool they have selected. The operator should choose a type of holder that is capable of holding the cutting forces of the tool. End mills should never be put into a drill chuck. When installing the tool into the tool holding device, the operator should engage as much of the solid shank of the tool as possible, generally within ⅛” of the flutes. Likewise, the tool should never be gripped over the flutes of the cutting edges.

Loading tools into and removing tools from the milling machine

Just like with all machining setups, cleanliness is going to be key when loading tools into the milling machine. Clean tools and holders reduce the chance of damage and help maintain the accuracy of the spindle and tooling. Modern manual milling machines utilize an R8 taper and a draw bar for securing tooling. Some tools, such as endmills, are held in R8 tool holders or R8 collets. Other tools, such as face mills, may be held by an integral R8 shank that is part of the tool itself. Generally speaking, twist drills are held in drill chucks unless there is a specific need to hold the tool tighter, and there is a collet in the same size as the drill shank. Holding a reduced shank drill in a ½” collet is a good example of this instance.

For safety, a box end wrench or vise handle is not recommended when tightening the draw bar. An open-ended wrench is safer because it cannot be accidentally left on the draw bar and, inadvertently, have the machine turned on. Not heeding this warning could result in the operator being injured, the machine becoming damaged, or the tooling being broken.

The following process is for loading and unloading tools from a milling spindle with an R8 spring collet as the holding device. The process is similar for loading integral shank R8 tools or end mill holders. The main difference is that end mill holders should have tools installed and removed from the machine before being installed into the spindle. On specific machinery in the shop, tightening or loosening tools in tool holders while in the spindle could be a hazard to the operator. This is a habit that should not be started.

 

“Step 2: Put the milling machine in gear if it isn’t already. If the machine is in neutral, the brake mechanism will not function.“

“Step 7: Hold the collet with the left hand, reach up to the top of the machine with the right hand, and engage the draw bar with a few rotations. The collet is now being held in the spindle by the end of the draw bar.“

“Step 11: Still supporting the tool, use the ¾” open ended wrench to tighten the draw bar until the spindle starts spinning.“

“Step 12: Grab and apply the spindle brake while continuing to tighten the draw bar until the appropriate torque is reached.“

“Step 12: Grab and apply the spindle brake while continuing to tighten the draw bar until the appropriate torque is reached.“