Lathe Tutorials

Lathe Operations

This section covers some of the lathing 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 lathes can do. THIS IS NOT A SUBSTITUTE FOR PROPER TRAINING OR TALKING TO A PROCTOR.

Turning

Turning is to feed the cutting tool along the length of the piece (along the Z-axis). This can be used to reduce the diameter of a part, create shoulders or create tapers.

Preferred: Right hand, carbide cutting bits

DO NOT USE: Parting tool

Facing

Facing is to feed the cutting tool perpendicular to the lathe's axis of rotation (along the X-axis). This creates a flat surface on the end or shoulder of the workpiece.

Preferred: Right hand, carbide cutting bits

DO NOT USE: Parting, 45° cutting tools

Parting

Also known as a cutoff operation, parting is to feed the cutting tool perpendicular to the lathe's axis of rotation in order to sever a section of the workpiece from the chucked section.

ONLY USE: Parting tool

Chamfering

Chamfering involves creating an angled surface at the edge of the workpiece or a shoulder. It can be done by feeding a 45° cutting bit along the X- or Z- axes into the workpiece, or by feeding a cutting tool at an angle.

For 45° chamfers: 45° cutting tool

For other: Right hand, carbide cutting bits

Drilling

Drilling uses a drill bit mounted in the tailstock of the lathe to create a hole in the end of a workpiece. This hole is aligned with the lathe axis. Countersinks and counterbores can be made using the same method.

Use: Drill bit, countersink, counterbore (ask a proctor for a box)

Tapping

Tapping uses a tap to create threads on the inside of a hole at the end of the workpiece. To do this, use a spring-loaded tap guide mounted in the tailstock and a tap mounted in a tap holder. The tap is then turned by hand to create the threads.

Use: Tap, tap handle, tap guide

DO NOT TURN THE LATHE ON

Reaming

Reaming uses a reamer mounted in the tailstock to finish a hole at the end of the workpiece. The reamer is fed into the workpiece, refining the surface of the hole and improving the hole size tolerance.

Use: Reamer (ask a proctor)

Threading

Threading creates an external thread on the surface of a workpiece, by synchronizing the feed of the cutting tool with the rotation speed of the lathe. The lathes have a specific setting for threading.

Use: Threading tool / insert (ask Drew)

Knurling

Knurling creates a patterned "knurled" texture of straight, angled, or crossed lines are rolled onto the surface of the workpiece, which is effective for adding grip to tools, or as decoration.

Use: Knurling rig (ask Drew)

Profiling/Grooving

Profiling involves creating more complex shapes in a workpiece using a combination of different feeds and/or tools. Grooving is similar to parting, except that the tool is only fed partially into the workpiece, such that no segment of the part is severed.

Form Turning

Form turning involves using a specifically created cutting tool to create more complex shapes in the workpiece. To perform form turning, a custom cutting tool is machined, hardened, and ground.

Boring

Boring involves the use of a boring bar to create a large inside diameter on the end of a part. Boring differs from drilling in that the boring bar is mounted as a cutting tool, not in the tailstock, the bar moves parallel to the axis, and larger or nonstandard diameters can be created.

Cutting Tools

This section will detail an assortment of tools that can be used with the lathe, what they look like, and what they are for. To use cutting tools that you can't find at the lathe 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 - What cutting tool to use based on type of operation?

Tool Post - Mount these in the quick-change toolpost near the lathe chuck. There are lots of other types; these are the ones used most in the shop.

Right Hand Cutting Bit

The HSS (high speed steel) right hand cutting bit is ideal for turning (reducing diameter) and facing. Remember that the corner of this bit is rounded, so account for this radius when machining!

Carbide-Insert Cutting Tool

The carbide cutting bit can be used for a variety of cutting operations, including turning, facing, and shallow grooves. Use this tool whenever you're working with harder materials like harder steels!

45° Cutting Bit

The 45° cutting bit is ideal for creating chamfers at the end of a part. I don't know why you'd use it for anything else...

Parting Tool

The parting tool is useful for performing parting/cutoff operations (shocker, I know). It can also be used to make grooves in your part.

Threading Bit

A threading bit is used for single-point threading, which synchronizes the feed and speed to create external threads on a part.

Knurling Tool

A knurling tool is used for knurling, creating textured patterns on the external surface of a part. The rollers are pressed against the workpiece to create an impression of the pattern in the part.

Tailstock - Mount these in the tailstock, which points axially toward the chuck/workpiece. These are the ones most commonly used in the shop.

Drill Bit

Hopefully you've heard of these before. Use them to drill a hole in the end of your workpiece. If you're using a large-diameter drill bit, start with a smaller pilot hole and/or a combination drill-countersink.

Reamer

Reaming perfects the finish of a hole that has already been drilled, and ensures greater precision in the hole diameter. Be careful, as reamers are relatively delicate. Don't jam the reamer too far into the part!

Combination Drill-Countersink

These are used for starting holes and leaving a small countersink at the edge of the hole. They're especially useful if you're planning on tapping a hole, and they're great as pilot holes for larger bits.

Countersink

Countersinks are used for creating a countersink, or internal chamfer, on the edge of a hole that has already been drilled in the end of the workpiece. Use this after you've drilled a hole!

Tapping Setup

Creating internal threads in drilled holes uses a three-piece tapping setup. The cutting tool is the tap, which is secured in the tap handle, also known as a tap wrench. The tap wrench is pushed into the hole by a spring-loaded tap guide, which is mounted in the tailstock. The tap handle is turned and counterturned a little at a time, which cuts threads into the interior surface of the hole. Remember to use cutting fluid and avoid driving the tap too deep, which will break either your threads or the tap. DO NOT TURN THE LATHE ON WHEN TAPPING.

Other - These aren't cutting tools, but they can be useful. Talk to a proctor about how to use these!

Live Center / Dead Center

These can be used to support the end of a piece for greater precision, which is especially useful for longer parts, which tend to flex at the end furthest from the chuck. Live centers spin, dead centers don't! Also used for aligning the lathe axis.

Steady Rest

Just like centers, steady rests stabilize longer or more flexible parts to ensure that the far end of the workpiece stays in alignment with the lathe axis. Use the steady rest as an alternative when centers can't be used.

Indicator

Indicators are precision measurement tools that are used to ensure alignment. They can be used to center the lathe axis, align the tool post, check parallelism of the workpiece, centering stock in the lathe chuck, and much more. Used with an indicator base.

Lathe Feeds & Speeds

Cutting Speeds

Because a lathe rotates the part past the cutting tool instead of rotating the cutting tool itself, calculating speeds for the lathe is a little different than calculating speeds for the mill, drill press, or other machines. When using a lathe, the cutting speed is calculated in surface feet per minute (SFM/SFPM). This accounts for the circumference of the workpiece, which may vary greatly. Different materials and cutting tools necessitate different SFMs, 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 SFM rate. The softer a material is, the higher the SFM 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 SFM, the lathe only specifies cutting speed in RPM. To use the chart below, follow these steps:

1. Identify the material you are turning, and locate the appropriate row in the Cutting Speeds chart.
2. 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!
3. 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.
4. Convert your selected SFM to RPM using this formula: RPM = (3.82*SFM) / Diameter
5. Use the dials on the lathe to specify the correct RPM.

Cutting Speeds_Lathe.pdf

Common Feeds & Speeds

This is a copy of the feeds and speeds poster that can be found posted next to every lathe in the shop.

Autofeed

The Harrison lathes in the machine shop (not the Monarch) feature an autofeed function that automatically moves the tool holder of the lathe in the X- or Z-axes. Autofeed is good for getting a uniform finish, really slow operations, or operations that take a long time. Note that autofeed is not an advanced feature, and will not stop unless you pull the lever. Therefore... LATHES ON AUTOFEED SHOULD BE SUPERVISED AT ALL TIMES.

Choosing a feed rate

First, calculate the appropriate feed rate for your machining operation using the speeds and feeds chart posted next to each lathe. If you're working with a common material, find the feed rate from the poster posted next to every lathe in the shop (reproduced above: Common Feeds & Speeds). Feed rates are listed in inches/revolution or mm/revolution.

Using the bottom chart on the headstock, find your desired feed rate. Use the F columns. Note that the left chart is in inches per revolution, and the right chart is in millimeters per revolution. Identify the corresponding gearbox sequence (e.g. AR1X).

Setting a feed rate

To set the feed rate, use the four dials at the bottom of the headstock panel. According to the gearbox sequence you identified from the table, turn the dials so that they are aligned to the appropriate gears. For example, if you read AS8X, you would align the dials as shown in the picture. Only change the top three (letter) dials when the lathe is off. The bottom (number) dial can be changed when the machine is running, but try with the machine off first.

Engaging autofeed

The direction of the feed is set using the feed axis selector. Push this knob IN to select Z-axis feed (parallel to axis) and OUT to select X-axis feed (perpendicular to axis).

The autofeed is then engaged by lifting or depressing the feed engage lever. Lifting makes it go one way, and pulling it down makes it go the other way. Test it out far away from your part first!

NOTE: The autofeed will only start feeding once you turn the lathe on.

For a more detailed autofeed tutorial, click here

Single-Point Threading

A tutorial for creating external threads on the surface of a part. This is suitable for large threads. For smaller threads, use a die instead. Make sure you know what you're doing and get familiar with the lathe before you even consider trying this! For more information, talk to Drew.

Threading on a lathe.pdf

Troubleshooting

Chattering

If the cutting tool is making scratching sounds while machining, this is called "chatter." When your tool chatters check for the following:

Tool bit is dull - Switch out the tool bit and give the dull one to the shop proctor.
Tool bit is on loosely - Tighten the tool bit with the hex at your station.
You are cutting too much - Try removing a little less material per pass (shallower depth-of-cut)
Your cutting speed is not adequate for this material - You might be going too fast or too slow. Make sure you're working with the suggested cutting speed.

Chip Color

Chip colors can indicate whether your cutting speed is too fast. If your chips are the same color as the material, you are at an appropriate speed. If they are copper-colored, then you are at the upper limit of appropriate cutting speeds. If the chips are blue, purple, or black, then your piece and the tool bit are really hot. If this happens:

Stop the machine and let the tool and piece cool down.
When you start cutting again, go slower and use more cutting fluid. You may want to try removing less material per pass.
If your chips are still running hot, talk to a proctor. You might have a dull cutting bit, or you might be using the wrong cutting speed.

From left to right: Good temperature, silvery; be careful, coppery; too fast, blue; way too fast, purple

Measurements are off

Are you reading off the DRO? Be sure to make measurements with calipers when accuracy is important. The digital readout is a helpful tool, but your piece might be out of spec if you are relying only on the readout for measurements. Have a set of calipers or a micrometer on hand to accurately measure the dimensions of your part. Better yet, keep a set of calipers AND a micrometer, and check with both. The different measurement methods will keep you in spec all the time. Measure well, measure often!

Digital Readout is in the wrong units

To change between inches and millimeters, press the period button on the DRO.

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