Machinists like to live on the edge, but they always want to know precisely where it is. If you’ve watched any machining videos (*cough*) then you’ve seen heavy use of digital readouts on machines. A “DRO” (as the cool kids call them) is a little computer that knows where the slides are, and thus where your cutter is on the piece. However, there’s a catch. DROs don’t know the absolute position of the spindle, they know the relative position of it. The bottom line is that a DRO is just a fancier version of the graduated scales on the hand wheels. The key difference is that the DRO doesn’t suffer from backlash, because it is measuring the slides directly (via glass scales similar to your digital caliper) rather than inferring position from rotations of the leadscrews. With traditional hand wheels, you have to compensate for backlash every time you change direction, and a DRO saves you from that (among other convenience features).

The point is that, whether old school or new, you still only get a relative coordinate system on your part. You need to establish an origin somehow. A useful way to do this is to set an origin at one corner of the part, based on its physical edges. How do you tell the DRO (or hand wheels) where the edges are? Enter the edge finder.

Precision Beyond Measure

The humble edge finder is one of those tools that are so commonplace in manual machining that everyone has forgotten how clever they are. It’s just a shaft with a precision ground stub on the bottom of it that is free to float around laterally (with some spring tension on it). This shaft is of a precise (and known) diameter — typically something conveniently halved like 200 thou or 6mm. You’ll see why this matters in a moment.

When chucked in the mill, the edge finder’s stub will wobble around like crazy, because it’s free to do so. To use it, you run the spindle at a moderate-to-high RPM (say 1000) and bring the wobbling end up to the workpiece. As the edge finder contacts the part, the wobbling end will become more and more concentric with the arbor of the tool.

So here’s the trick, and what makes the device so clever. In principle, when the wobbling end is precisely touching the surface, the edge finder tool will be running perfectly concentric. However that’s pretty much impossible to see by eye. If it’s close-but-not-quite concentric, you won’t be able to tell. To get around that, the spring tension holding the wobbling end is calibrated such that the spinning surface will “grab” the part and gain traction right as it becomes concentric, causing it to kick off to the side as it tries to roll along the surface. This is visible as the wobbling end “kicking-over” to one side. There is some technique here to get a perfect reading, because if you continue cranking the table past that kick-over moment, your reading won’t be precise. However, with proper technique, this very simple device is extremely precise and repeatable.

Going Halfsies From Tip to Spindle

Once you’ve found that edge, you know that the edge of the tool and the edge of the material are in the same place. However, what you want is for the center of the tool (and thus your spindle) to be on that edge. This step is easy, because as we said earlier, the diameter of the edge finder’s tip is known. Simply raise the tool clear of the work, and continue moving in that direction by the radius of the tool (as shown on your hand wheel or DRO). You can now set your DRO (or hand wheel) to 0 in that dimension and repeat in the other dimension. You’ve now got an origin in a known location, and by extension a coordinate system across the whole part. There are many types of edge finders (including electronic ones commonly used in CNC), but the basic cylindrical wobbling type is common, inexpensive, and precise. Three things that machinists love!

Avoid Tolerance Stacking

One final note — when making your own mechanical drawings, it’s always helpful to pick one corner of each surface from which to mark all your dimensions and locations. Edge finding is a main reason why. If all your numbers are relative to the same corner, the machinist only has to edge-find once, and there will be less accumulated error from resetting the origin. Either that, or the machinist has to do math to recalibrate all the numbers you gave to be relative to the same place. Both scenarios will make said machinist angry. Help heal the generations-old rift between engineers and machinists by minding your origin. If you don’t, expect to someday find a chuck key on the wrong side of your broken window.

Machining is one of those fascinating fields that bridges the pre-scientific and scientific eras. As such, it has gone from a discipline full of home-spun acquired wisdom and crusty old superstitions to one of rigorously analyzed physics and crusty old superstitions.

The earliest machinists figured out most of what you need to know just by jamming a tool bit into spinning stock and seeing what happens. Change a few things, and see what happens next. There is a kind of informal experimentation taking place here. People are gradually controlling for variables and getting better at the craft as they learn what seems to affect what. However, the difference between fumbling around and actually knowing something is controlling for one’s own biases in a reproducible and falsifiable way. It’s the only way to know for sure what is true, and we call this “science”. It also means being willing to let go of ideas you had because the double-blinded evidence clearly says they are wrong.

That last part is where human nature lets us down the most. We really want to believe things that confirm our preconceived notions about the world, justify our emotions, or make us feel better. The funny thing about science, though, is that it doesn’t care whether you believe in it or not. So go get your kids vaccinated, and up your machining game with scientific precision. Let’s take a look.

Ditch Your Gut and Trust the Science

In the cutting edge world of modern machining, we must trust the science. We’re optimizing for the long tail of efficiency now, and gut feel doesn’t cut it anymore. On high end CNC equipment, spindle traversal speeds are in the neighborhood of 25 inches per second (about 64 cm per second). A wise machinist once said, “At those speeds, the E-Stop button is entirely decorative”. More importantly, at these speeds, physics really really matter. Crashing a spindle at full rapids on an $80,000 machine is not something your boss lets you forget.

Proper chip formation is now something we understand at a very basic level, thanks to modern tools like finite element analysis. We can perform simulations of the physics that are happening at the tool/material interface, and perform experiments to determine the optimal tool angles, cutting fluids, and so forth. When you’re trying to remove material as efficiently as possible, while minimizing tool wear and maximizing surface finish quality, this level of understanding becomes necessary.

The Physics of Better Surface Finishes

For example, machinists have long known that 8-15° is the ideal back rake for a cutting edge when machining steel. On the lathe, this manifests as the angle at which the top surface of your tool bit is ground to fall away from the cutting edge.

Through modern physics and simulation of the machining process, however, we now also know that, if the angle and speed are just right, the steel chip can actually enter a plastic flow state as it encounters this back rake surface. This optimizes the speed at which that steel gets out of the way, increases material removal efficiency, and prevents buildup on the cutting edge (which compromises surface finish).

We’re going to be talking more about how we know what we know in machining, so watch this space. Until then, find the oldest machinist in the room and ask them what they know, because it’s a lot more interesting than reading research papers, and gets you 80% of the way to the same place (but keep your rapids at 20% for now).

“Everything is a spring”. You’ve probably heard that expression before. How deep do you think your appreciation of that particular turn of phrase really is? You know who truly, viscerally groks this? Machinists.

As I’ve blathered on about at length previously, machine tools are all about precision. That’s easy to say, but where does precision really come from? In a word, rigidity. Machine tools do a seemingly magical thing. They remove quantities of steel (or other materials medieval humans would have killed for) with a slightly tougher piece of steel. The way they manage to do this is by applying the cutting tool to the material within a setup that is so rigid that the material has no choice but to yield. Furthermore, this cutting action is extremely precise because the tool moves as little as possible while doing so. It all comes down to rigidity. Let’s look at a basic turning setup.

Spring Forces Illustrated on a Lathe

The colored arrows show some of the major spring forces that a machinist will know and feel. First and foremost is the downward pressure on the tool bit (red). This is, in turn, trying to torque the rear of the toolpost upwards (green). The toolpost is then trying to torque the rear of that cross-slide downwards (blue), and the whole setup is torquing the far end of the carriage upwards on the ways (yellow). Meanwhile, the tool pressure is driving that tail stock (brown), and the spindle bearings (purple) upwards.

Everything is a spring, and these are but a few that you’ll find in the simplest of machine tools. If any of these sources of springiness fails to hold up its end of the job, the result will be chatter, imprecise cuts, or the machinist picking shards of parting tool out of her forehead. None of those are good outcomes.

The Machinist’s Rigidity Aresnal: Mass and a Perfect Fit

The weapons we have in this fight for rigidity are primarily two in number. First and foremost is cast iron. By sheer mass it can be made rigid inexpensively, and it is also good at absorbing harmonic vibrations which can make any rigidity problems elsewhere much worse. The second weapon is precision fitting parts. If we can minimize movement where the parts connect to each other, we eliminate sources of spring. This is difficult when those parts need to slide, but that’s why we have things like dovetails and adjustable gibs. These are features that allow parts to slide relative to each other in one dimension, while moving as little as possible in all other dimensions. It’s all about murdering the foul demon of spring that threatens the glorious and righteous kingdom of rigidity.

So, next time you hear the phrase “everything is a spring”, pour one out for your local machinist. Sure, the mechanical engineers will go on about it, but it’s the machinists who Really Know.

Let’s say you’ve recently bought a lathe and set it up in your shop. Maybe you’ve even gone and leveled it like a boss. You’re ready to make chips, right? Well, not so fast. As real machinists will tell you, you can use all the levels and lasers and whatever that you want, but the proof is in the cut. Precision leveling gets your machine in the ballpark (machinists have very small ballparks) but the final step to getting a machine to truly perform well is to cut a test bar. This is a surefire way to eliminate any last traces of twist in the bed.

There are two types of test bars. One is for checking headstock-to-ways alignment, which is what we’re doing here. There’s another type used for checking tailstock alignment, but that’s a subject for another day.

We start by chucking some stock. You want something of a substantial diameter, because we’re going to have a lot of unsupported stick-out, something you would normally never do. The stock needs to be as rigid as possible on its own. The more stick-out you have, the more precise your measurement of bed twist will be, but the test becomes impossible if stick-out is too much for the stock to remain rigid while cutting. It’s a tricky balance. For this demo on my small bench-top machine, I’m using 1-¼” diameter stock, 5″ long. For a large floor-standing machine, 2″ diameter stock around 10″ long is a good place to start.

Dial it in as close as you can in the four-jaw chuck. The more run-out we eliminate now, the quicker and easier this test will be. If you have stock with a machined surface, that’s ideal, but cold-rolled stock from the factory is generally fine. I’m using mild steel here, but something like 12L14 free-machining steel would make it easier to get a good finish (which helps with the measurements).

The general idea is that we’re making a barbell shape. We’ll make high-precision cuts on the ends, while leaving a narrower area in the middle that we can easily skip over.

With the stock dialed in, turn down a relief area in the center of the bar, leaving about an inch on each end untouched. We’ll only be measuring the ends, so the middle section will just be in the way. Making a relief also minimizes tool wear between cuts (which would affect our test results). A relief of 30-50 thou is sufficient. We want just enough room to clear a few test cuts on each end. Don’t relieve too much, because we need that rigidity in the stock.

Note that we’re not using the tail stock for support here. This is important because the tail stock introduces its own set of variables that affect alignment. We’re only testing headstock-to-ways alignment, so we can’t use the tailstock. This means we have to make very light cuts because our rigidity is very low.

With the relief made, we can now take very light cuts in the two measurement areas. We want just enough to clean up the surface all the way around (so we know we’re inside any runout in the chuck). I’m making two-thousandth cuts on each pass here. Make your pass on both measurement areas, without touching the cross-slide in between. Stop the machine at the end and measure, then wind the carriage back and do another cut as needed.

Once you have a clean cut on both measurement areas, compare the diameters with a high quality micrometer. If they are different, the machine is cutting a taper, which means your bed has some twist. Adjust or shim the lathe’s tailstock-end feet a little bit and make another cut.

A larger tail-end on the bar means the front-right corner of your ways is too low (the toolbit is getting closer to the work as it travels). If the chuck-end of the bar is larger, the front-right corner of your ways is too high (the tool bit is getting further away from the work as it travels).

How close you want to get these measurements is up to you, but a tenth of a thousandth over 5-6″ is likely good enough for anything a hobbyist is going to need. Once you’re done, you can oil and store the test bar for use later on. With a relief cut of 30 thou or so, the same test bar can be reused several times.

That’s all there is to it! Cutting a test bar is an easy hour-long project that will teach you valuable lathe skills and build your confidence in the machine. Once you know you can trust the machine, you’ll know that any future problems exist only between the hand-wheels and the drawing*.

*That’s you.

Let’s say you’ve gone and bought yourself a sweet sweet metal lathe. Maybe it’s one of the new price-conscious Asian models, or maybe it’s a lovely old cast iron beast that you found behind a foreclosed machine shop. You followed all the advice for setting it up, and now you’re ready to make chips, right? Well, not so fast. Unlike other big power tools, such as band saws or whatever people use to modify dead trees, machine tools need to be properly level. Not, “Hurr hurr my carpenter’s level says the bubble is in the middle”, but like really level.

This is especially true for lathes, but leveling is actually a proxy for something else. What you’re really doing is getting the entire machine in one plane. Leveling is a primitive way of removing twist from the structure. It may not seem like a huge piece of cast iron could possibly twist, but at very small scales it does! Everything is a spring, and imperceptible twist in the machine will show up as your lathe turning a couple thousandths of taper (cone) when it should be making perfect cylinders. All this is to say, before making chips, level your lathe. Let me show you the way.

If you have a bench-top machine, start by leveling the bench to pathetic carpenter’s standards. That is, level it with any old bubble level such that a pencil won’t roll off. Personally, all my benches use grade 8 bolts as feet, which makes leveling a breeze.

The next step is to acquire a quality machinist’s level. These differ from hardware store bubble levels in several key ways. First, they are incredibly sensitive, typically reading less than five thousandths of an inch displacement per foot (or less than 0.5mm per meter). Second, they can be self-calibrated. Third, they have precise ground surfaces on at least three sides, and a V-shaped bottom to minimize error from mating with the machine’s surface.

Calibrating the Level

Every time you use a machinist’s level, you need to calibrate it. The cool thing about a level is that they are “self-proving”. Here’s how that works.

First, place the level on a clean and dry granite surface plate. Rotate the level until you find an axis that is level. There will always be one, because the granite plate is a plane (as good a one as humans can make anyway) and any plane will have one axis that reads level.

Next, place a heavy straight edge against the level, such as a 1-2-3 block or an angle plate. This holds your reference. Now you can flip the level 180°, place against the reference edge, and check it again. Using the calibration screw on the level, split the difference so the bubble reads halfway between those two readings. You’ll need to go back and forth a few times. Try to touch the level as little as possible. The heat from your hands will warm it up and cause it to change shape sufficiently to lose your calibration.

The goal is to get the level to show “zero” in both directions. As you close in on this, you’ll need to find new axes that are more level to use as reference. Once you get zero both ways, it has self-proven and calibration is complete.

Leveling Your Machine Tool

Next, place the level on the ways (the machined parts where the tailstock slides) of the machine, down near the tailstock. Make sure the ways are clean, dry, and free of raised burrs. A 1-2-3 block may be needed for the level to sit flat. If you use blocks for this, measure them first to make sure they are the same. Inexpensive 1-2-3 blocks may not be! Precision-ground gage blocks are better, if you have them.

For a floor standing machine, adjust the feet until you get a level reading. If your machine has a lot of feet, try the “three point” method. Get your machine sitting on only three of its feet (or two feet and a screw jack). A triangle is much easier to get level. Once level, carefully lower the remaining feet until they take weight but don’t upset the level.

For a bench-top machine, you’ll typically shim under the feet of the machine as needed. A variety pack of steel shim stock in various thicknesses is helpful here, or sacrifice an old feeler gauge.

Do the same procedure for the ways near the headstock, and also with the level placed lengthwise on the ways. You’ll likely need to go back and forth a few times until every position reads level.

Another school of thought says that, instead of placing the level on the ways, you should place it on the cross-slide, since that’s where the cutting tool is. Personally, I think this just introduces new sources of error, but I like to double check on the cross-slide after the ways are level.

Be Zen About Releveling

Leveling is not a one-time deal, so get comfortable with it. The machine needs to be re-leveled any time it is moved, and periodically as the floor shifts or settles. Even concrete moves, so check your machines from time to time and re-level as needed. You should also check a new machine after using it for a few weeks, as the machine’s castings will “settle in” under the vibration of use. Check it again any time you suspect the machine is turning a taper, such as if you’re struggling to hit a dimension on a long part. Older machines are more flexible and will need re-leveling more often.

Once your machine is level, the next step is to really dial it in by cutting a test bar. This is a topic for a future article, so stay tuned for that. In the mean time, stay away from those carpenter types. Apparently that “wood” stuff is ruined by fire. Why would anyone bother with it?

You say to yourself, “Self, I want, nay, need a lathe”. Being a good little trooper, you then did all your research, having chosen Import or American, Imperial or Metric, and all your feed options and such. You then pulled the trigger and the machine is en route to your shop. Now what?

Choosing a Spot for a Serious Tool

First and foremost, you need to figure out where to put it. Sure, you probably should have done that before you bought it, and maybe a pulling a tape measure would have been a good idea. Never let pesky details like that get in the way of buying something cool, though. You can make room. How badly do you really need a refrigerator? In a pinch you could sleep under the workbench and gain all that space taken up by the bed. Get creative in your shop layout.

If you bought a bench-top machine, you will of course need bench space for it. Some smaller machines, such as watchmaker’s lathes, can be stored in a cabinet and pulled out for use. Anything larger will need a permanent home, and should be bolted to the heaviest bench possible. The more mass you can inject into the system, the fewer issues you’ll have with tool chatter. Mass also damps vibrations when turning stock off-center or spinning up oddly-shaped things. Make sure the bench location you choose is close to power, because extension cords are to be avoided for machine tools. You’ll also likely need a bit of room behind the machine to access fuses and such.

If you bought a large floor-standing machine, be aware that these often require access to the back side of them for some types of adjustments and setup. This can mean anywhere from a few inches to several feet, depending on the machine. Large lathes are often placed in the middle of a shop partly for this reason. Big lathes also often need access to an overhead crane or chain fall for changing large chucks, or manipulating heavy stock.

Regardless of the type of machine, make sure to leave space to the left of the headstock. You need room for long stock to protrude through the spindle. If you’re limited to only working on stock that fits entirely inside the spindle, you’ll limit your projects quite a bit, and you’ll be forced to waste a lot more stock.

I also recommend giving a thought to cleaning. Machine tools throw chips everywhere, and all the shields and trays and guards in the world won’t prevent it. Make sure you’ll be able to clean in, around, and behind the machine. You don’t want oily chips piling up forever. In some cases, this can even be a bit of a fire hazard.

Next, you want to look down and see what’s there. If your shop is in a bouncy castle, you’re no doubt having fun, but perhaps machining is not for you. (Small children also tend to gum up the change gears, which are a hassle to clean.) A concrete floor is ideal, whether under the machine itself, or under the workbench the machine is sitting on. Wood floors are not ideal for a floor-standing machine, because it shifts and warps. Less stable flooring can be okay, but you’ll need to re-level your machines more often. The same goes for mounting a bench-top machine on a wooden bench.

Delivery Day is About Heavy Lifting

With all that sorted out, it’s time to think about taking delivery. New bench-top machines are likely to come on a pallet. Unless you have a loading dock, that means you’ll need lift-gate delivery service, which costs extra. If you’re buying used, don’t assume the seller has any way to put it in your truck. You’ll also need a way to get it off your truck and on to your bench in your shop. An engine hoist (sometimes also called a cherry picker, engine picker, or shop crane) is a great tool for all these jobs. They fold up nicely and are incredibly useful for lots of things around the shop. The rule of thumb for these is to get one at least double the size you think you need. If your machine weighs around 300lbs, get the 2-ton crane. The reason is that the ratings for these are based on the shortest extension of the lifting arm, which renders them useless. They operate (typically) at one-quarter their rating at full extension of the arm. Note that engine hoists can handle up to medium-sized floor-standing machines as well. Just make sure you really know how much it weighs.

For a large floor standing machine, you’ll need to get more creative for loading in your truck. Forklifts and front-end loaders are a good option, and can be easily rented. If the seller has a gantry crane or overhead chain fall hoist of some sort, that’s also good. Failing all that, it is possible to winch them up a ramp on to a trailer, but don’t underestimate the difficulty of this for 3000lbs of cast iron. It can easily be an all-day job to load this way, and it’s not the safest option. Unloading is the reverse of loading, as the saying goes (not really — I just made that up). If your machine came with a manual, be sure to follow the lifting instructions therein. Machines often have an unintuitive center of mass, so it can be tricky to know where and how to lift it. Use proper lift slings and good crane etiquette. This means absolutely no meat parts under the load at any time, be in control of the momentum, and always assume the worst is about to happen.

Once in your shop, floor-standing machines can be moved with various methods. A pallet jack is a great option if the machine is already sitting on something that allows you to get under it. Failing that, a common method is to go Full Egyptian. You can jack up the machine a little at a time and slide round steel bar stock under it. With a piece every foot or so, you can roll and slide the machine with a large prybar. It’s possible to move huge machines by yourself using this method.

I’ll close with the word that sows dread into the heart of every machine shop enthusiast. That word so heinous that many dare not speak it aloud: Stairs. Yes, the real world often has stairs in it, and people have moved huge machines down narrow basement death ladders. The first rule of doing this is to reduce weight as much as possible. Tear the machine down as far as you can. I’ve seen people strip lathes all the way down to a bare ways in order to slide pieces down the stairs one at a time. If you’re doing a restoration project, this is no big deal because you were going to dismantle it anyway. Plan ahead for this, though. It can be a long project in itself to dismantle a large machine, and you don’t want to be doing that on your front lawn on a school night in the rain.

Once you get your machine in situ, it’s time to get set up. Next time we’ll talk all about the fine art of lathe leveling.

Lathes are complicated machines, and buying one requires weighing a lot of options. We’ve already talked about buying new Asian, or old American machines (with apologies to the Germans, British, Swiss, and all the other fine 20th century machine tool making-countries). We also talked about bed length and swing, and you ain’t got nothin’ if you ain’t got that swing. Let’s talk about the feature set now. If you’re buying new, you’ll shop on these details. If you’re buying used, knowing the differences will help you pick a good project machine.

Imperial or Metric?

First and foremost — Imperial or metric? If you’re buying a new machine and you reside outside North America, the answer is, of course, metric. If you’re in North America, however, the choice is less clear. The gut instinct may be to go metric because it’s modern and “obviously better”, right? Well, not so fast. Most stock, hardware, and tools in North America are still more readily and cheaply found in Imperial sizes. You can go all metric, but you will be swimming against the current. That ivory tower has a lot of stairs, so think hard about how badly you want to sit in it.

The next statement will shock and anger many of you, but here goes. For machine tool work, there is minimal practical difference between the two systems of measurement. Both have advantages and disadvantages. Before the Metric Squad spools up their decimal angry commenting machines, allow me to explain.

For dimensioning tasks in the typical range of machine parts (say, smaller than your hand), Imperial is easier. Thousandths are very convenient because everything is an integer, and common tolerances for press fits, hole clearances, etc, are all easily expressed and measured. With metric, you’re dealing in fractions of a millimeter, and there’s a lot of decimal points.

When working with hardware, such as drilling and tapping holes, choosing and measuring fasteners, and so forth, metric is definitely nicer. Metric drill sizes are easier to manage than the wacky Fraction-Letter-Number system that Imperial evolved into. The relationships between holes, threads, and fastener dimensions in metric are logical and easy to manage. With Imperial, you tape a chart to your wall and look at it a lot.

My personal recommendation is to be comfortable with both. Either machine can do both, though all tasks will be easier in the system the machine is designed for. Choose measuring tools that have both systems. Lots of the best books on machine shop theory and practice were written before metric existed, so be bilingual in your systems of measure.

Powering These Powerful Tools

For newer Asian machines, an exciting new option exists — brushless DC. These lathes get a lot of torque for their size. One horsepower for 10amps is typical, and that’s a lot of power for a small machine. You also get infinitely variable speed control for free, which is a huge advantage (especially when you’re first learning the dark art of feeds and speeds).

Choosing Power Feed Options

The next thing to think about is power feed. Most lathes have it, but it comes in many forms. Power feeding is valuable because it yields better surface finishes, and takes much of the tedium out of long operations. It’s also how single-point thread cutting is done — the drivetrain is synchronized to generate the right helix for the thread you need.

Almost all machines will have a half-nut that clamps to the lead screw for cutting threads. The cheapest machines will also rely on this for power feed. The next level up in quality will have a separate clutch (in addition to the half-nut) for driving the carriage. This is typically done with a keyway that runs the length of the lead screw. A keyed gear in the carriage taps power off this, without engaging with the threads of the lead screw. This is a nice compromise because you don’t wear out the leadscrew threads, but the machine remains inexpensive. Larger and higher-end machines will have a dedicated driveshaft running parallel to the lead screw to drive the carriage. You may see multiple shafts running parallel, some for power transmission, some for various control functions. It gets crazy up there in the clouds with the likes of Monarch and Lodge & Shipley.

Benchtop machines typically only have longitudinal power feed (the carriage, or “X-axis” if you like). Some higher end bench top machines are now starting to offer power cross-feed as well, and this is a very nice feature if you’ll be facing larger diameter pieces. It also helps get smooth parting operations. Larger machines will have power cross-feed de rigeur.

The final element of power feed is the driving of the lead screw. This can be done with change gears, a transmission, or some combination thereof. Low end machines will have only change-gears, which means you need to physically swap out gear sets for every change of feed-speed that you want. This is the road to hell. Look for a quick-change gearbox with three or more speed options. Some also have a reverse feed option, which is a nice touch, because you can cut left-hand threads. Higher-end machines will have transmissions as complex as a tractor, with all manner of speed and direction options. These are great to use, but be wary of complex gear boxes if you’re doing a restoration project. It’s easy to underestimate the complexity of the drivetrain in these beasts, and many are filled with unobtainium parts that were abused by some gear-jamming rig jockey of years past.

Tool Posts

Now let’s talk tool posts. These days, lower end machines will have a four-way tool post, which holds one cutting tool, and three things to slash your hand open when you brush past them. Tool height is set with shims and a lot of swearing.

For a little more money, you can generally get a Quick Change Tool Post. On these, tool height is set with a thumbscrew on the tool holder, and the setting is permanently “saved” with each tool. QCTPs are all pretty much based on the Aloris design of years past. Cheaper ones will have a piston lock, slightly better ones will have a tapered wedge lock. Both are fine. Let’s be clear on this point: get a quick change tool post. It will change your life (and get you addicted to tool holders). Just make sure it’s a standard size, like AXA or BXA. Otherwise you’ll spend a fortune on tool holders, and trust me, you never have enough tool holders. I throw a couple on the invoice with every order I place at suppliers like MSC Direct or LittleMachineShop, and it’s still never enough.

Really old machines will have “lantern” tool posts, which use a curved wedge to set tool height and angle. Purists like these for the old-timey aesthetic, but they aren’t very rigid and you had best not be in a hurry when setting one up.

Chucks, Rests, and Other Accessories

The last major thing to look for is what accessories the machine comes with. If you only get one chuck, make it an independent four-jaw. It’s easily the most versatile. Three-jaw scroll chucks are a convenience (and they are turbo convenient) but you will need an independent four-jaw for true precision work. You also want a faceplate for all the odd-shaped things. Exotic options include a collet chuck, 4-jaw scroll chuck, and six-jaw chucks. These are very expensive new, but older project machines often come with great stuff like this. Buy all these extra chucks new if you are made of money or because you hate me and want to send me photos of nice things I can’t have.

Also worth noting are the rests. Any machine should come with a steady-rest, which is used to support the end of a long piece when the tailstock would be in the way. Less commonly used is the follow-rest, which rides on the carriage and applies counter-pressure to the back side of where the tool is cutting. This is useful for working on long thin pieces, where the work would deflect under cutting pressure. New machines will come with both rests, but old used machines may not. These can be hard to find for a vintage machine after the fact, so try to make sure you get a steady-rest, at least.

Weigh These Options Carefully

If you’re shopping for a lathe (and you should be) you’ll quickly find that every machine differs along one of these vectors. There are a lot of choices, even within the same brand and size range, so research carefully. When buying new, I recommend downloading the manuals for the machines to see exactly what features they have. When buying used, learn to scrutinize grainy flip-phone photos on craigslist for desirable details like a separate drive shaft for the carriage or a dusty old collet chuck sitting in the back. Like buying a car, buying a machine tool is an exercise is cross-referencing the features you want with the features you can afford, to find your own sweet spot.

Happy lathe shopping! Next time we’ll talk about getting ready to receive your new machine, and setting up its new home in your shop.