CNC Tooling Basics

Types of Tools

Center Cutting End Mills  Center Cutting End Mills  Can be used for plunging in pockets, face milling, end milling, and side milling.  May have two or more teeth.  Most versatile tool in your library.

Non-Center Cutting End Mills  Non-Center Cutting End Mills  Can really only be used for side cutting  Can NOT be used for plunging.  May have two or more teeth.  Their advantage is that they are inexpensive.  Not recommended for a CIM class lab, as they will break easily if used to plunge.

Ball End Mills  Ball End Mills  Great for milling complex surfaces.  Can be used for decorative edging operations like fluting or beading.  May have two or more teeth.

End Mill For a Surface?  Do NOT use an End Mill to perform a surface operation, as the tool will leave square ridges that will have to be removed by sanding or some other secondary operation.

Stepover  Stepover is defined as the space between passes of a tool during an operation. Inventor HSM defaults to 95%, which will take a long time to machine. By changing the value to 1/2 the diameter of the tool, it takes much less time.  Also, the smaller the tool, the smoother the surface.  1. Machine time = 8.49 minutes  2. Machine time = 3.51 minutes  3. Machine time = 6.41 minutes 2. 1/2” ball mill,.25 stepover 3. 1/2” end mill,.125 stepover Surface to be machined 1. 1/4” ball mill,.125 stepover

Depth of Cut  Sometimes a pocket or other operation is too deep to cut all at once; this is when we make more than one pass to finish an operation.  A good rule of thumb in your classroom is the depth of cut should be ½ the diameter of the tool.  A ½” end mill therefore would have a depth of cut of 0.25” A ½” tool is used with a 0.25” depth of cut on a pocket 0.75” deep.

Fly Cutter or Shell Mill  Fly Cutter or Shell Mill  Great for facing operations on larger machines  Usually have 4 or more replaceable carbide or ceramic teeth.  They are very heavy, and require a larger machine with a lot of horsepower to make it work.  NOT recommended or made for the smaller Intellitek machines.

Engraving Tools  Engraving tools are great for decorative work with a milling machine.  Tools are generally small diameter, and require care so as not to break them.  Depths must be kept very shallow, as do feed rates when using them.

Roughing End Mills  Roughing end mills are used to remove a lot of material quickly, but leave a very rough finish and must be followed by a finishing pass.  Not recommended in a classroom to cut Renshape and other soft modelling materials, as it will require more time and a tool change to do a finishing pass with a different tool as well.

Number of Teeth (or flutes)  Each cutting tool on a mill is attached to a groove called the flute, that pulls the chips away from the material being cut.  General rule of thumb: The harder the material you’re cutting, the more teeth you need.  The fewer the teeth, the more space between them. This is called chip space.  More chip space is necessary with softer materials like some forms of aluminum. Teeth Flutes

Chip Load  The thickness of material sheared away by each cutting tooth is called the feed per tooth, or the chip load.  The chip carries away with it some of the heat from the milling process.  This is why number of teeth on a tool can be very important; too many teeth, or the wrong speeds and feeds, and the flutes can get clogged with chips causing the tool and part to overheat and produce a poor cut.

Cutting Tool Materials  High Speed Steel (HSS)  Very inexpensive, but works well with Renshape and other soft modelling materials.  Wear quickly and break easily when cutting harder materials.  Carbide-tipped  More expensive, but works well when cutting metals.  Lasts much longer and stays sharper when cutting modelling materials.  Allows you to increase speeds and feeds.  Solid Carbide  Very expensive, and very brittle. Not recommended for cutting modelling materials.  Coatings:  Some tools come with coatings that give them special properties. The most common is TiN (Titanium Nitride) This provides extreme hardness and heat resistance, and allows you to increase speeds and feeds.

Climb Vs. Conventional Milling  Milling tools can advance through the material so that the cutting flutes engage the material at maximum thickness and then decreases to zero. This is called Climb Milling.  Cutting in the opposite direction causes the tool to scoop up the material, starting at zero thickness and increasing to maximum. This is called Conventional Milling.The fewer the teeth, the more space between them. This is called chip space.

Climb Vs. Conventional Milling  Conventional milling causes the tool to rub against the cutting surface, work hardening the material, generating heat, and increasing tool wear. Raking chips across the finished surface also produces a poorer surface finish.  Unless specifically recommended by the tool manufacturer for the material being milled, always use climb milling on a CNC. Climb milling produces far less cutting pressure and heat, leaves a better surface finish, and results in longer tool life.  Cutting in the opposite direction causes the tool to scoop up the material, starting at zero thickness and increasing to maximum. This is called Conventional Milling.The fewer the teeth, the more space between them. This is called chip space.

“What Tool Should I Use?”  Center cutting end mills are the work horse, and can be used for almost every operation, except surfaces.  Surfaces are best cut using ball end mills. Change the Step Over for smoother finishes.  The shorter the tool you choose, the more rigid it will be. This will allow for greater accuracy and less chance of breakage.  The more teeth, the smoother the finish at calculated speeds and feeds.  The larger the tool, the more efficiently it will cut: less machine time.