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Mill Operations
Mill Operations
This section covers some of the milling operations that you will see and use in the machine shop. They are listed in order from most common to least common. Information about the tools used for each operation is in the next section, Cutting Tools. These descriptions are to help you understand what mills can do. THIS IS NOT A SUBSTITUTE FOR PROPER TRAINING OR TALKING TO A PROCTOR.
Drilling
Drilling
Drilling is to create a hole in the workpiece by feeding a drill bit in the Z-axis (vertically). Using a mill to do this allows you to locate holes with more precision than using a hand drill or drill press. You should drill to start the slot in your E4 hammer head.
ONLY USE: Drill bits (in drill chuck)
Plunge Milling
Plunge Milling
Plunge milling is to feed an end mill into the workpiece to create a vertical hole. Use plunge milling for overlapping holes, or when entering a part to start a pocket/slot. For individual holes, especially in harder materials, use a drill bit instead. (Use this technique for widening the slot in your E4 hammer!)
Preferred: Center-cutting end mill (in collet)
DO NOT USE: Drill chuck, non-center-cutting end mill
Shoulder/Contour Milling
Shoulder/Contour Milling
Shoulder or contour milling is to remove material from the outer surface of a part. This is good for shaping parts and creating flat faces. Keep in mind that you can create convex right angles, but not concave right angles.
Preferred: Flat end mill (in collet)
DO NOT USE: Drill chuck!
Pocketing
Pocketing
Pocketing is to remove material from the inside of a workpiece to create a cavity, or "pocket". You start by plunging into the part in the Z-axis. Then, cut in the X- and Y-axes to remove material. Again, convex right angles, but no concave right angles.
Preferred: Any end mill (in collet)
DO NOT USE: Drill chuck!
Grooving/Slotting
Grooving/Slotting
Grooving and slotting is to remove material in a straight line, usually the X- or Y-axis. Start either by plunging or entering the outside surface of the part. You do this to create the slot on your E4 hammer!
Preferred: Any end mill (in collet), T-slot cutter (ask Drew)
DO NOT USE: Drill chuck!
Tapping
Tapping
Tapping is to create internal threads in a part. You can do this either by drilling a hole and then tapping by hand, or by using a combination drill-tap. You should use manual tapping for your ocarina and hammer head. If you need a combination drill-tap, ask Drew!
Preferred: Tap, tap handle, tap guide
DO NOT: Turn on the mill!
Alternative: Combination drill-tap
Countersinking
Countersinking
Countersinking is to create a chamfer on the edge of a hole or slot. This can be used for sinking a flat head cap screw flush to the surface of a part, making it easier to press fit parts together (like your hammer hard face!), or just breaking an edge to deburr it. Do this before tapping, too!
Preferred: Countersink tool (ask a proctor)
Facing (Mill)
Facing (Mill)
Facing is to create a flat surface on the top of the workpiece. This can be done either using a regular end mill or a face mill, which has more cutting surfaces specifically for creating flat faces.
Must use: End mill, face mill (ask Drew)
DO NOT USE: Drill chuck (of course)
Facing (Fly Cutter)
Facing (Fly Cutter)
Facing is to create a flat surface on the top of the workpiece. This can be done using a fly cutter, which can create a very fine surface finish. However, do not try to remove too much material at once!
Must use: Fly cutter (in collet)
DO NOT USE: DRILL CHUCK
Counterboring
Counterboring
Counterboring is to remove some of the material around a hole or slot, in a cylindrical profile. (Compare to countersinking, which creates a conical profile.) Used to sink bolt heads below the surface of a part, so that the top surface is flat.
Preferred: Counterbore tool
Can also use: End mill
Boring
Boring
Boring is to create a large-radius hole in the workpiece using a boring bar. This allows you to create big holes, but is a little more complex than just using an end mill. For most applications, program the mill to mill a pocket in a circular path instead.
Must use: Boring head, boring bar (ask Drew)
Chamfering
Chamfering
Chamfering is to remove material from the edge of a workpiece, resulting in a slanted surface where two faces meet. You would can do this using a chamfer end mill, but you can also mount your part at an angle.
Preferred: Chamfer end mill (ask Drew)
Reaming
Reaming
Reaming is to finish a hole using a reamer. This creates a better surface finish and hole size tolerances. ONLY feed in the Z-direction, and do not bottom out the reamer.
Must use: Reamer (ask a proctor)
Broaching
Broaching
Broaching is to remove material in linear strokes by using a broach. This is done by mounting the broach in the spindle and using it to remove material vertically. Useful for creating shaft keyways and right-angled channels.
Must use: Broach
Dovetailing
Dovetailing
Parts can be constrained in 2 dimensions using dovetails, which are trapezoidal slots cut into the workpiece, with walls sloped inward. Because dovetails have overhangs, a special dovetailing end mill must be used.
Must use: Dovetailing end mill
Cutting Tools
Cutting Tools
This section will detail an assortment of tools that can be used with the mill, what they look like, and what they are for. To use cutting tools that you can't find at the mill stations, speak to a proctor!
This is NOT a manual or substitute for training by a proctor. Before you do anything new, speak to a proctor and/or Drew. Be safe!
Tool Selection
Tool Selection
What cutting tool do I use based on the type of cut I want?
What cutting tool do I use based on the type of cut I want?
End Mills
End Mills
What are the different types of end mills? How do I choose?
What are the different types of end mills? How do I choose?
Flutes
Flutes
In addition to being musical instruments, "flutes" are also what we call the channels in drill bits and end mills! When choosing an end mill, one of the main points to consider is how many flutes you want your cutting tool to have (ranging from 2 to 8 flutes). Changing the number of flutes has various effects on your milling operation. MOST IMPORTANTLY, USING END MILLS WITH DIFFERENT FLUTE COUNTS CHANGES THE REQUIRED FEED AND SPEED WITH WHICH YOU MILL (see Feeds and Speeds, below). MORE flutes means LESS chip evacuation, requires a SHALLOWER depth of cut, BETTER surface finish, and a STRONGER cutting tool. The opposite is true for less flutes. Read on to learn about the most common flute options (2- and 4- fluted end mills) and why you would use each! As always, if you're not sure, talk to a proctor or the shop manager!
Two-fluted
Two-fluted
Two-fluted end mills are generally used for softer materials such as plastics and aluminum. When cutting these materials, you can use higher feed rates and remove more material per pass. Because the flutes are comparatively larger, the cutting tool is a bit weaker, but can push more chips out of the way. This is important because 4-fluted end mills may not be able to evacuate chips fast enough, resulting in poor surface finishes and poor tolerances.
Four-fluted
Four-fluted
Four-fluted end mills are generally used for harder materials, such as steels. When cutting these materials, you need stronger, more rigid cutting tools, cutting at lower feed rates and shallower depth of cut/stepover. Having 4 flutes basically means that you get 4 shallower cuts per revolution, instead of 2 big cuts. This can give better surface finishes, but may also lead to smearing of material on the cutting edges, if chips aren't evacuated fast enough.
Shape
Shape
End mills also come in different shapes. This usually refers to the "nose" of the end mill (the end of the end mill?). Different shapes result in different profiles being cut into the workpiece. There isn't much to think about when choosing these; just choose whichever shape you want your part to have. Here are some examples of the most common end mill shapes.
Square
Bull-nose (Corner Radius)
Ball
Chamfer / Taper
Other cutting tools
Other cutting tools
What can I use that isn't an end mill? How do I use it?
What can I use that isn't an end mill? How do I use it?
Drill Bit
Drill Bit
Use drill bits in drill chucks! Use them to drill straight holes. These holes can be blind (stop somewhere in the part) or through-hole (go all the way through the part).
Tap
Tap
Taps are used to create internal threads within a hole that has already been drilled. Use these with a tap guide on the mill to get very straight threads!
Reamer
Reamer
Reamers create nice surface finishes and very good tolerances in holes. Use by first drilling a hole with a drill bit or end mill, then plunging the reamer in slowly. Don't ream too far into the hole!
Fly Cutter
Fly Cutter
Fly cutters are used to create very fine surface finishes on flat faces. Mount one in a collet and pass it over the surface, taking off very little at a time.
Face Mill
Face Mill
Face mills are used to create large flat surfaces on a workpiece. These can remove a pretty large amount of material, but don't give the best surface finishes. Use like an end mill, but pay attention to the limited cutting surface!
Counterbore Tool
Counterbore Tool
Counterbore tools are used to create counterbores! First, drill a hole with a drill bit or end mill, then follow with a counterbore tool. The smooth cylindrical end of the counterbore tool will fit in the drilled hole and guide the cutting edges.
Countersink Drill Bit
Countersink Drill Bit
Drill/countersink combination bits can be used to start holes and set countersinks before drilling, especially with larger holes. Regular countersink bits are good for... well, making countersinks!
Combination Drill-Tap
Combination Drill-Tap
Combination drill-taps are a fast way to create tapped holes in a part. ONLY use with CNC, since you have to time the feed and speed perfectly.
Boring Bar
Boring Bar
Boring bars can create large interior holes. The diameter will be relatively accurate, but the surface finish can be a little poor. Easier to use on a lathe than a mill. Talk to Drew if you would like to use one!
Broach
Broach
Broaches are used to create linear shapes within parts by slowly removing material in small linear passes. Used to create keyways and small channels/grooves. Talk to Drew if you would like to use one!
Fixturing
Fixturing
Fixturing is to secure your workpiece to the mill table, so that you can safely (and accurately) remove material from it! This section gives a brief introduction to fixturing different types of piece properly, using different methods. Fixturing properly is CRUCIAL for safety in the shop!
This is NOT a manual or substitute for training by a proctor. Before you do anything new, speak to a proctor and/or Drew. Be safe!
Fixturing Flowchart
Fixturing Flowchart
What fixturing options are there for my type of stock?
What fixturing options are there for my type of stock?
Vise
Vise
By default, our mills are fixtured with a vise aligned properly to the mill table. If you can, simply clamp your piece securely in the vise jaws and get to work!
Parallels
Parallels
Sometimes, your piece is a bit too short to fit in the vise. In addition, you might want to drill through your workpiece (and not into the mill table!). The solution is to use a set of parallels to hold up your piece! These very flat steel bars sit against the jaws of the vise and keep your piece elevated. You can get creative with arranging these!
Hex Block + Collet
Hex Block + Collet
If your piece is round, and has a standard diameter, you can mount it in a hex block using a lathe collet. You can then clamp the flat sides of the hex block in a vise using parallels. This method is especially good if you need to machine holes at different angles in a cylindrical piece, since the hex block maintains the orientation of your piece!
Wee-vees
Wee-vees
Unfortunately, not all round pieces fit into lathe collets. When this is the case, you can use a set of wee-vee blocks! These V-shaped blocks provide 4 points of contact to securely hold your part in place on the mill.
Strap Clamps
Strap Clamps
Strap clamps hold your piece directly to the mill table by sliding into the T-slots in the table and tightening the nut until the strap clamp tightly holds your piece down. These are good for larger pieces, and can be used in a variety of configurations, including with step blocks or 1-2-3 blocks. However, be careful not to run into your clamps when you're milling. Ask a proctor!
Toe Clamps
Toe Clamps
Toe clamps are somewhat similar to strap clamps, but instead of holding your workpiece down from the top surface, they push inward from the sides, leaving the top open for milling operations. These are a bit trickier to set up, but their low profile makes them easier to use with some CNC programs that require traveling over the top surface of the part.
Soft Jaws
Soft Jaws
Sometimes, you may need to hold irregularly shaped pieces in the vise. When this happens, you can machine temporary custom jaws out of wood, plastic or aluminum to hold your piece. You can even 3D print them for low-stress fixturing! These are referred to as "soft jaws".
Rotary Vise
Rotary Vise
A rotary vise acts like a lathe chuck to hold your parts at varying angles relative to the mill table. You can then turn the rotary vise using the handwheel (or CNC-driven motor) to mill at different angles, or create curved profiles in shapes.
Other Mill Tools
Other Mill Tools
We've talked about cutting tools and fixturing, but those aren't the only items used in machining on a mill! Here are some other useful tools to know about and use on/around the mill.
Drill Chuck
Drill Chuck
Drill chucks can support a variety of drill bits without having to switch to a bunch of different collets. The drill chuck can ONLY be used for cutting exclusively in the Z direction, such as when using a drill bit or reamer.
Collet
Collet
On the mill, collets are used to securely hold cutting tools, drill chucks, edge finders, etc. so that they can be used on the mill. As opposed to lathe collets, mill collets have INTERNAL threads.
Edge Finder
Edge Finder
One of the most important tools in the shop, the edge finder allows you to determine where your zero point should be on the digital read-out (DRO). Spin it at high speeds and watch as it deflects to know when you've just barely hit the surface of a part.
Deadblow/Lead Hammer
Deadblow/Lead Hammer
Mainly used to make sure parts are snug against parallels/the vise. Tighten the vise most of the way and give your workpiece a few firm strikes with the hammer to press it down and make sure it is parallel. Can also be used for aligning the vise on the table. These are better than other hammers because they don't rebound and/or damage your tooling. Not recommended for taking out your pent-up frustration.
Vise Stop
Vise Stop
Used to save time zeroing a workpiece over and over. For parts that are symmetrical and need operations on multiple faces, or for when you need to make multiples of an identical part. Zero once on your first part and set the vise stop. After that, you can just align to the stop and not zero the mill anymore!
Indicator
Indicator
Indicators are used for precise alignment for accurate fixturing. This is important for setting up a vise, or fixturing parts with strap/toe clamps. Align the tip of the indicator along a flat face that is supposed to be parallel to a mill axis. As you move the mill axis, the indicator dial will tell you how far that face is from parallel. Can also be used to check for circular-ness, planarity, etc. if you're creative!
Quill Stop
Quill Stop
The quill stop is an often-underutilized tool that allows you to set a maximum or minimum height to which you can move the quill (how far you can pull the handle), without locking the quill in a single place (like the quill lock does). This is really good for making sure that you don't drill into the vise or mill table! If you can, set the quill stop to just above the mill table surface before you fixture your part.
Speed Handle
Speed Handle
The speed handle on the vise has four shorter handles rather than a single long handle (which is standard on most vises). It can be taken off if it gets in your way!
Basket / End Mill Holder
Basket / End Mill Holder
A small plastic bin and a funnel-shaped end mill holder are provided for users to handle sharp end mills. Use the plastic bin to catch end mills as you eject them, and use the end mill holder to push the end mill upward as you set the cutting tool into the mill.
Mill Feeds and Speeds
Mill Feeds and Speeds
Cutting Speeds
Cutting Speeds
Often, you will see mill cutting speeds reported in revolutions per minute (RPM), which is the value the mill reads out. However, while RPM tells you the speed at which the spindle is spinning, it does not necessarily tell you how fast your tool is cutting! This is because cutting tools have different diameters, so the tangential velocity at the cutting edge (the "cutting speed") varies from tool to tool, even with the same RPM. Instead, cutting speed should be calculated in surface feet per minute (SFM). Different materials and cutting tools necessitate different SFPMs, and these are listed in the table below. These specifications are based on material properties; generally, the harder a material is, the lower the appropriate SFPM rate. The softer a material is, the higher the SFPM should be. Note that the listed ranges are starting points, and depending on the coolant, depth of cut, and desired finish, you may want to adjust the numbers. If your chips start turning blue, purple, or black, turn down the RPM.
Although cutting speeds are specified in SFPM, the mill only specifies cutting speed in RPM. To use the chart below, follow these steps:
Identify the material you are milling, and locate the appropriate row in the cutting speed chart.
Identify the material of the cutting tool you are using. HSS (High speed steel) cutting tools are bright silver or gold, and carbide cutting tools are dark grey/black. See the section above for more info!
Select an appropriate SFM within the specified range. For roughing passes with relatively large depth of cut, use a lower speed. For finishing passes, use a higher speed to achieve a more uniform surface finish.
Convert your selected SFM to RPM using this formula: RPM = (3.82*SFM) / Cutting Tool Diameter
While the mill is OFF, select either high or low gear. Turn the mill ON, then turn the small handwheel to specify the correct RPM.
Feed Rate
Feed Rate
Feed rate is the speed at which you feed your material into the cutting tool. This is especially relevant for autofeeding and CNC operations, which allow you to precisely control the speed at which your material passes the cutter. In our shop, feedrate is usually measured in inches per minute (IPM). To identify the proper feed rate:
Identify the material you are cutting and find the appropriate row in a table (like the one below). Find the maximum allowable chipload.
Identify the RPM you will use, using the steps above in Cutting Speeds
Count the number of flutes your end mill has (usually 2 or 4)
Multiply Chipload*RPM*# of Flutes to get your feed rate in inches per minute.
(Optional) Program this into the DRO to autofeed, or write it into gCode/CAM for CNC operations.
Mill Glossary
Mill Glossary
You might hear a lot of new terminology in the shop (or in the information on this page). Here are some illustrations and explanations for some of the words you might see associated with milling!
Feed
Feed refers to how fast you are moving the cutting tool through the workpiece. This can be in the X- and Y-axes (pictured above), or in the Z-axis when plunging, drilling, or ramping. Usually measured in inches per minute (IPM).
Speed
Your spindle speed, usually measured in surface feet per minute (SFM/SFPM) and converted to revolutions per minute (RPM), is how fast your cutting tool is spinning.
Depth of Cut
Also known as "axial depth of cut", measures the height of your cutting pass.
Stepover / Width of Cut
Also known as "radial depth of cut", measures how much your tool moved laterally into the piece since your last pass.
Climb Milling
Viewed from the top, cutting tools almost always rotate clockwise. Climb milling means the cutting tool moves around the part as if the cutting tool is pulling it along the surface, like a wheel. Around a contour, this means the cutting tool travels clockwise around the perimeter.
Conventional Milling
The opposite of climb milling, conventional cutting feeds material into the cutter against the direction of the cutting tool. This usually means the cutting tool takes a counterclockwise path around the perimeter.
Surface Finish
Surface finish refers to the pattern/texture that is left on the surface of a part after it has been cut. Every operation leaves a unique surface finish, with different tolerances, feel, and function. Get a nice surface finish by using a slow-feed, high-speed finishing pass that takes off very little material!
Chip Evacuation
Chips are the material that gets removed by a cutting tool. Once material is cut by the edge, it has to go somewhere, such as through the flutes in an end mill or cutter. Chip evacuation is important for achieving good surface finishes and keeping tools sharp/undamaged.
Troubleshooting
Troubleshooting
Fine Z-control
Fine Z-control
Basics
Basics
To use the fine z-axis control:
Use the lever below the fine z-axis wheel to engage the wheel (push to the left)
Make sure that the wheel itself is engaged. If you're turning it and nothing is happening, it probably means that it isn't engaged. Turn the wheel so that the little notch behind the wheel goes in the hole facing the wheel.
When you're done, disengage the fine z-axis wheel by pushing the lever mentioned in step 1 to the right. If you don't disengage the wheel, you won't be able to move the coarse z-axis adjustment lever.
If the fine z-axis control won't move…
If the fine z-axis control won't move…
Push the black lever under the z-axis wheel (circled in the picture) in. That lever locks the spindle in a mode that allows you to use the wheel to control the z. By pushing the lever in, you unlock this mode.
Handwheels won't move
Handwheels won't move
Check the DRO to see whether the autofeed is engaged! When the autofeed is active, the handwheels cannot be moved by hand.
Collet is stuck in the mill (especially Mill 2)
Collet is stuck in the mill (especially Mill 2)
One of the most common mill problems occurs when you try to use the tool changer without putting the z-axis all the way up. This can cause the collet to get stuck in the mill. To fix this problem, follow these instructions. If you're not a shop proctor, ask a shop proctor to do this for you.
Turn the circuit breaker off
Put the quill stop at the top and lock the z-axis lever in place
Using the hex wrench on top of the CNC monitor, unscrew the three screws on the power drawbar (gold cylinder). Make sure to keep track of these screws. (Use a stool in the main shop to reach these)
Take off the gold cylinder (power drawbar).
Turn the rod (drawbar) that you see after taking off the gold cylinder to screw in the collet. Once the rod is stuck in place, loosen it 1-2 turns.
Put the gold cylinder back up and retighten the three screws. (Make sure these line up with the actual holes)
Put the hex wrench back on the CNC monitor, and see if your collet will come out.
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