Metal Lathe 101

This introductory course provides the instruction and practice necessary to safely begin using the metal lathe for your own projects. In a small group setting, students will learn basic safety, and practice the fundamental techniques of facing, turning, chamfering and drilling/boring to precise dimensions.

It is important to note that this course provides the bare minimum of practical skills to safely use this versatile tool. The student is highly encouraged to use the additional resources provided to further their understanding.

Metal Lathe Drop-In Rate: $45/day (12pm to 9pm)

Tools/Materials

Carbide inserts
Digital Calipers
Cutting Fluid
Aluminum Stock
Samples of already machined parts

General Shop Safety

Safety glasses or face shield
Closed toe shoes
Full length pants
Long hair, drawstrings and shirt tails/sleeves tucked in/ tied back, no dangly jewelry, rings, watches.

Safety Considerations

Metal lathe injuries typically fall into one of the following categories:

Blunt force injury, i.e., being struck by a large flying object like the chuck key or a loose part. This is most likely to happen when someone leaves the chuck key in and turns the lathe on. The rule is, if the chuck key is in the chuck, your hand is on it. If you do that, you will never leave it in.
Eye injury from flying chips. Always wear safety glasses. Look at your work, not under it. If you’re concerned, wear a full face shield.
Entanglement in rotating machinery.
Cuts or splinters from handling swarf. Never move it out of the way with your hands. Steel swarf will slice you like razor blades.
Cutting tool injury. The tools themselves are pretty sharp. Don’t touch the cutting edge. If you’re messing with the chuck be aware that if you move the wrong way you could hit the tools.

To avoid or mitigate these injuries:

NEVER leave the key in the chuck. (Do not let go of the key while it is in the chuck.)
Protective eyewear MUST be worn. Note, a full face shield offers the best protection.
Locate and ensure you are familiar with the operation of the ON/OFF starter.
Faulty equipment must not be used. Immediately report suspect machinery.
No loose or dangling clothing, gloves, jewelry or long hair.
Keep hands away from all moving parts. (NEVER touch the rotating work-piece, even with sandpaper.)
Open belt cover to engage safety cutoff when working/measuring near any potentially moving parts, and to avoid accidentally hitting the on button.
Make sure everything is clamped firm and tightly. If it’s a thin wall part, put something inside to support it.
Before pressing the start button, give the chuck a quick spin to make sure you won’t hit it.
When using cutting fluid, and if the lathe is turning, come in from the right hand side.
Check underfoot to ensure no slip/trip hazards are present.
Do not lean on the lathe or base. More generally, maintain a stable working stance.
Do not take overly aggressive cuts. If it feels or sounds wrong, it probably is.
If unsure about the proper feed rate, slower is better (safer).
Never reach into a turning lathe to remove swarf. Stop the spindle and clear with pliers.
Never leave the lathe running unattended.
Do not attempt to slow/stop the rotating chuck by hand.
If a chuck is too heavy for you to safely lift and install, ask for help.
Keep the bed and slides of the machine clear of tooling.
Leave the lathe in a clean, tidy state.

IMPORTANT: You must report all mishaps that result in injury, tool damage and/or breakage.

Specific Goals

By the end of this course, the student will have practiced how to:

Name and identify the key components of the lathe
List most of the safety rules covered (and contained in the handout)
Secure raw stock in the 3-jaw chuck
Select an appropriate tool for the desired cut
Secure a tool in a holder, load the tool into the quick-change tool post, and align the tool on-centre
Look up and set an appropriate spindle RPM using the belt pulleys
Disengage the power feed (to allow manual advance)
Face the end of raw metal stock
Turn a piece of raw metal stock to a precision diameter
Drill a hole using the tailstock (in preparation for tapping)
Time permitting, bore a hole
Cut a chamfer using the compound slide
Change from one chuck to another (3-jaw to 4-jaw or vice-versa)
Part off a finished piece

Additionally, the student will be aware that:

● Parting-off on this lathe is problematic and requires caution
● A process exists for aligning a part in the 4-jaw chuck
● A process exists for cutting imperial threads on this lathe

Useful/Required Tools

The Machining Lab has many of the tools needed to craft precision parts on the lathe. This includes quick-change tool post mounting blocks, various tool-holders (that accept your own inserts), a live centre, a Jacob’s chuck for the tailstock, dial and dial test indicators, etc.

You will need to provide the following:

Digital caliper
Tooling inserts (these can be purchased at the front desk)
Cutting fluid (can use WD40 for aluminum)

Liability

If damage to the lathe or community tooling occurs owing to a violation of a listed safety rule, the member will be financially liable for any repairs or replacement parts. Further, access to the lathe may be revoked at MakerLabs’ discretion.

About the Metal Lathe

This is a Hercus 260 lathe. It has a self-centering chuck. The cutters that are used are single point cutters, and you want to have a single point engagement while cutting. Only use tools that have inserts. The carbide inserts can be switched out if they break.

Parts of the Lathe:

It can cut a variety of metals including:

Aluminum
Plastic (Acetal/Delrin, UMHW)
Brass
Bronze
Cast Iron
Copper
Carbon and Alloy Steel
Stainless Steel

Tooling

It’s important to understand how a single point cutter functions, especially the various relief angles that provide clearance. These terms also apply to insert tooling.

Source: https://learnmechanical.com/single-point-cutting-tool/

To understand how this geometry affects the actual cut, this short YouTube video is highly recommended: https://www.youtube.com/watch?v=bUrp8JMRwx4.

The American National Standards Institute (ANSI) has developed a coding system of numbers and letters to describe the shape, dimensions, and important parameters of turning inserts.

This PDF has detailed information on insert tooling nomenclature, use, etc.

https://www.machiningcloud.com/wp-content/uploads/2019/08/MachiningCloud_TurningToolsAndTheirApplication.pdf

Surface Speed by Material and Operation

The table below is applicable for high speed steel tooling. When using carbide tooling, increase the cutting speed by a factor of 2-4. All speeds are in SFM (feet/min). To convert from SFM to RPM or vice versa, use the following formulas (where DIA is the diameter of your workpiece in decimal inches):

RPM = SFM x12 / DIAx3.14 or SFM = 3.14/12 x RPM x DIA

Source:

https://www.cnclathing.com/guide/cutting-speed-chart-for-different-materials-in-turning-drilling-and-more-cnc-machining-processes-cnclathing

How It Breaks

Running a tool into the headstock.
Going too deep into the machine, and the tool gets grabbed by the machine.

*** Please note: If damage to the lathe or community tooling occurs owing to a violation of a listed safety rule, the member will be financially liable for any repairs or replacement parts. Further, access to the lathe may be revoked at MakerLabs’ discretion.

Start-up Checklist:

Follow the oiling/lubrication procedure. Each port should get one pump of the oiler.
Open the belt cover to preclude accidental starting of the spindle.
Check that the job is clamped tight in the chuck.
Check that the toolpost and tool are secure.
Make sure your tool is on-centre height of the spindle.
Ensure the correct speed for the machining process is selected.
Press paddle safety’s green button.
Check for potential crashes. Move the carriage as close to the chuck as needed, set a stop, and manually rotate the chuck to confirm clearance. (Note, this step will also discover a chuck key inadvertently left in the chuck.)
Stand to the side and “pulse” the start button to reconfirm safe operation

Setting up the Machine

Get your geometry right before loading the tool. The tool holders are specific to the type of tool rest.

Adjusting the Tool Post

The tool post will need to be adjusted to your stock when you initially set-up your material, and once progressing further into your project as the size of the stock decreases.

The post can be removed with a hex key.
Spacer. Might need to use a different spacer to get the vertical range of motion that you need.
Slide the tool post into position, tighten by hand, and then tighten with a hex wrench. You want it to be secure … but please do not overtighten.
The tool tip should be on centre. If you’re too high or too low, you run the risk of damage to the tool, and it could get sucked in / snap off.
Instructors should be familiar with disassembling and reassembling the Swiss toolpost. This process should be demonstrated to students.

Adjusting the Gears / Lead Screw

By adjusting the gears, you can adjust the speed of the lead screw.

A = Faster

C = Slower

Change the lead screw with the handle to change the direction that the lathe moves.

If the carriage is moving, and you want to override it, just hold onto the clutch.

The belts determine the RPM. There’s a belt on the side, and a belt at the top. The feed is in Inches per Revolution. You can’t get a better finish by playing with the belts.

Each increment on the dial is .001” (One-thou). 0.040” (40-thou) is about 1mm.

Types of Cuts

Facing

While the lathe is spinning, come in and touch off the material until it starts to generate a chip. Move slightly to go across the face of it. Not very much movement is necessary, only go to the middle of the material.

You can feel the cutter pushing back on you if you try and cut too much. If this happens, back off on the amount you’re taking off. If you see the curls coming out, you’re cutting the right amount. You want nice short, small chips coming off the lathe.

Turning

Before you start turning, set up the stop. Your setting will prevent you from crashing the tool or cross-slide into the spinning chuck.

Move the wheel to the end of your material.
Touch off from the material
Slowly walk up the material using the apron handwheel
If it makes a humming sound, the tool is rubbing. If it’s consistent you can overheat your tool. When this happens, you’re not taking a deep enough cut, or you’re going too slow and rubbing the tool.

Drilling

Drilling operations require a special chuck.

Insert the drill chuck into the tail stock.
Make sure there is enough extension on the tailstock barrel. (Retracting the barrel will unseat the drill chuck or live centre.)
Use an appropriate centre drill to provide purchase for the actual drill. Centre drill deep enough to engage the drill but stop short of the actual drill diameter.
Set the speeds according to the feed and speed chart.
As long as chips are coming out of both drill flutes, the speed is fine.
For deeper drilling, fully retract the drill periodically (“peck”) to clear chips and add cutting fluid to the hole and drill tip.

Boring

Boring refers to turning on the inside diameter of a part, i.e., widening an existing hole. It is more difficult than exterior turning as you can’t see the cutter.

Ensure the boring head fits into the hole with plenty of clearance. You might need to drill a larger hole for a boring bar to fit.
Ensure the boring bar’s insert is on centre (or ever so slightly below)
Use the minimum amount of tool stickout necessary to get to the depth you need.
Set up a dial indicator to accurately measure depth
Take light passes, remembering that winding the cross-slide dial CCW pulls the cutter towards you and therefore deeper into the material.

Resources:

Quinn Dunki (BlondiHacks)

“Lathe Skills”, an introductory 21-part YouTube series on using the metal lathe

https://www.youtube.com/playlist?list=PLY67-4BrEae9Ad91LPRIhcLJM9fO-HJyN

Joe Pieczynski

“General Lathe Videos”, 30+ YouTube videos on metal lathe tips and techniques from a seasoned veteran

https://www.youtube.com/playlist?list=PL4wikbEbcE3JX4jfTVtgxEBWmENsACjyQ

https://www.cnclathing.com/guide/cutting-speed-chart-for-different-materials-in-turning-drilling-and-more-cnc-machining-processes-cnclathing

This PDF has detailed information on insert tooling nomenclature, use, etc.

https://www.machiningcloud.com/wp-content/uploads/2019/08/MachiningCloud_TurningToolsAndTheirApplication.pdf

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