This page is all about the vintage Craftsman metal lathe at the Hack Factory.
Craftsman 6”x18” metalworking lathe, built sometime after 1958 by the Atlas Press Company in Kalamazoo Michigan for Sears/Craftsman branding.
- model 101.21400
- s/n 015269
- 6” swing (3” center height over bed)
- 18” between centers
- multi-speed belt drive with back gears
- English thread cutting capabilities using manual change gears (metric thread pitches can be approximated)
- Timken tapered roller spindle bearings
- (add photos of the various name plates, links to good websites, etc.)
- External threading: 1”-10tpi
- Internal taper: MT2
- Through-hole diameter: ~0.5” (crudely measured)
- Internal taper: MT1
- Offset capability: unknown (used for turning tapers)
- retract ram fully to press out a stuck taper
- two-speed belt drive from motor to jackshaft
- four-speed belt drive from jackshaft to spindle
- optional back-gears for reduced speed (6.5 : 1 reduction) and increased torque (they should only be used with lowest few speeds, and the assembly must be lubricated before each us)
- Motor speed: 1790 RPM as measured (nameplate claims 1750 RPM, 1/3HP, 5.3amps)
Spindle speeds with back gears disengaged:
Spindle speeds with back gears engaged: (X means not advisable; not measured!)
(back gears should only be used with the lowest several speed combinations, and remember to oil the mechanism. Perhaps only use the backgears that result in a spindle speed under 100rpm.)
(Need to measure the T-slot in the compound rest…)
The original toolpost
Karl is considering purchasing a quick-change tool post made by A2Z CNC that fits the Craftsman. It will simplify the height adjustment and allow different tools to be installed painlessly and quickly.
The lathe has a set of change gears that can be combined in different configurations to change the leadscrew speed relative to the spindle speed. Larger ratios are used for threadcutting, and very small ratios are used for automatic feed when turning a smooth surface.
The leadscrew is a very precisely-made acme screw with 16 teeth per inch (TPI). The split-nut on the carriage engages it, as does the gear that rotates the threading dial. If the change gears are configured so the lead screw rotates at the same speed as the spindle (a 1:1 overall ratio), the machine will be set to cut the same 16tpi as the leadscrew. To cut 8tpi, the leadscrew is slowed down to half speed. To cut 32tpi, it is sped up to twice the spindle speed.
Every gear with enough room is marked with some variation of “M6-101” and the tooth count. Most of the gears have been marked with sharpie to avoid having to constantly count gear teeth or squint at the faint stamped numbers while setting up the machine. The gears are made from die-cast Zamak, a somewhat delicate material; please treat them gently to avoid damaging or breaking teeth.
- gear thickness: ~0.375”
- bore diameter: ~0.498”
- keyway width ~0.120” (two matched keyways 180 degrees apart)
- width between bottoms of keyways ~0.63”
Gears in the tool box: 20, 32, 36, 40, 44, 46, 52, 54, 56 Gears in use for the current configuration: (yet to be checked)
Common configurations: (make some graphics for feeding and threadcutting)
- 4” diameter body
- 2” from spindle register surface to front face
- s/n 6874 (stamped on back of chuck and on each jaw)
- marked “MODEL 101 21590” and “MADE IN ENGLAND” on face
- uses 1/4” square chuck key
A 3-jaw chuck is in the mail! Please note that scroll chucks are more delicate than independent-jaw chucks, and it is much easier to damage them or destroy their accuracy. Please only use the scroll chuck for precision work.
- 4” body diameter
- uses ??” square chuck key
Power tools can naturally inflict great bodily harm. On a vintage machine such as this lathe, there are more exposed moving parts than would be found on a more modern machine. Remember that this is from an era long before OSHA when people were required to be more mindful of their own safety, and slip-ups could be very costly. Moving belts and pulleys (there are plenty on this lathe) can grab fingers, hair, clothing, etc. and wind them in with great force/speed. It should go without saying that you need to be extra mindful and wear appropriate attire and safety gear when operating such a machine. Observers should also take appropriate precautions; especially eye protection.
- No long sleeves, baggy shirts, un-tied long hair, gloves, necklaces, wristwatches, rings, etc. People have lost fingers/hands and been killed by lathes by something as simple as loose hair or a wedding ring. Not kidding.
- Always wear eye protection. (recommend impact-rated safety glasses with side-shields)
- Avoid reaching over the spinning chuck or workpiece. (Yes, the belt tensioner lever is back there. Recommend waiting until the motor is stopped to reach for it.)
- Keep covers/doors closed when possible. (There is a door that covers the change gears and a cover over the headstock pulleys and backgears.)
- Unplug power to the motor while setting up the machine or changing configurations. (The motor plugs into a switched outlet mounted to the table; it's easy to use as a safety measure.)
- Leave the machine in the safest state possible when you leave. (unplug the motor, leave the belts de-tensioned, close covers, remove tooling, etc.)
Once you have a mind to protect your body, please also take into consideration the wellbeing of the machine. While it is heavy and powerful and massive, a lathe has countless exposed fragile parts and precision surfaces that need to be respected and cared for. The precision-ground surfaces of the ways on the bed are possibly the most vulnerable. Dropping heavy tools/objects on the ways or even simply setting tools and materials on them can cause irreparable damage to the lathe that could even render it useless. The ways are a precision-ground part of the machine, not a work surface to set things on. Other notable delicate parts include the leadscrew that drives the carriage along the ways and the surfaces of the Morse tapers in the spindle and tailstock ram.
If you don't understand exactly how a part or feature of such a machine works, please seek experienced help rather than taking an experimental approach. This machine is many decades old, and we would like to see it last many more.
This section will cover a variety of setup procedures and common lathe tasks. Note that it is NOT a substitute for proper training on the lathe, and these mini-guides all assume a general level of competency and knowledge.
Before you begin work, here are some things to check. Remember that you never know what the last user of the machine may have changed or reconfigured! There are numerous things that could be set in conjunction to cause major damage when the motor is switched on, such as the back gears being engaged at the same time as the spindle cone pulley, or the carriage feed being left engaged to slowly drive the carriage into the spinning chuck. Check absolutely everything, and you should not have any unpleasant surprises.
unplug motor for safety during setup (use the quick disconnect outlet/plug right next to the motor)
relax the belt tensioner (hopefully it was de-tensioned when you found the machine to avoid stretching the belts over time)
set the tumble-reverse gears to the neutral position
disengage the carriage feed half-nut
disengage back gears
verify that the spindle turns freely by hand and that it is locked correctly onto the spindle cone pulley
check both belts for general condition and proper routing
go through the lubrication procedures for the entire machine before starting it up
There are many bearings, bushings, and sliding surfaces that need to be oiled every day the lathe is used. Without this regular lubrication, the wear is accelerated and parts of the machine will wear out much more quickly in an irreparable manner. Remember, this is a precision machine tool, and the critical surfaces need to stay within tolerances less than a thousandth of an inch. Treat it with care!
Machine oil is used to lubricate all bearings on the machine, including the spindle's precision Timken roller bearings and also the numerous plain bearings on the machine. (Plain bearings are also commonly referred to as bronze bushings or babbit bearings.) Note that machine oil should not be confused with “motor oil” designed for internal combustion engines. Motor oil contains additives and detergents that are undesirable for this application. We keep Mobil SAE 20 machine oil in a squeeze bottle on the lathe bench for this purpose. It is amber like honey and clearly labeled.
Way oil is a thicker oil designed specifically to lubricate and protect sliding surfaces used by the carriage, cross slide, and compound slide. We keep Mobil Vactra way oil in a squeeze bottle on the lathe bench for this purpose. It is dark like maple syrup and clearly labeled.
A - OIL DAILY with S.A.E. No. 20 oil
B - OIL WEEKLY with S.A.E. No. 20 oil
C - OIL MONTHLY with S.A.E. No. 20 oil
D - KEEP CLEAN and well oiled at all times.
E - LUBRICATE gear teeth with Keystone No. 122 gear lubricant, or equivalent, to obtain smoother, more quiet operation. Remove oil and dirt before applying grease. %%*%%Remove screw to oil bearings with oil. %%*%%*About once a month clean with kerosene and a brush, then cover.
(lube chart source: http://www.atlas-press.com/tb_6lube.htm )
Some things I know can be incorporated: The back gear shaft really only needs to be oiled if the back gears are to be used, since they usually sit idle. Leave the tumble-reverse in neutral unless you are using the leadscrew. This saves needless wear on the gears and related assemblies.
Before installing a chuck or any attachment that threads onto the spindle, it is very important to carefully clean the mating parts of any swarf or debris. Use a clean rag to floss any debris from the threading and make sure no tiny bits of metal are left on either of the registration surfaces, or they will be smashed into place when the chuck is threaded on, both holding the chuck slightly askew and making the much more difficult to remove later. Clean these four surfaces:
- spindle threading
- spindle registration shoulder
- chuck threading
- chuck registration face
Lay a piece of plywood or a notepad on the ways to shield them from any potential damage while installing and removing chucks. Cradle the chuck in your hand and carefully thread it onto the spindle by rotating the spindle with the belt tensioner relaxed. This minimizes the chances of dropping the chuck on the ways and reduces wear on the threading because the weight of the chuck is not dragging on the threads as the chuck spins on and off of the spindle. Remember, these threads and the registration surfaces are very important for the accuracy of the lathe and need to be protected.
Removing a chuck is actually quite easy. The trick is to lock the spindle by engaging both the back gears and the normal drive pin at the same time. With the spindle thusly locked, rotate the chuck by hand to crack it loose. If it is very tight, you might try using the chuck key in one of it's usual sockets as a wrench for more leverage. Some people recommend grabbing one of the vice jaws with a crescent wrench or using a cheater bar between partially opened vice jaws, but please avoid this if at all possible.
Once the chuck is cracked loose, please unlock the spindle and remove it by cradling the chuck and rotating the spindle to protect the ways and save wear on the spindle threading.
DO NOT attempt to use the small indexing pin to lock the spindle for the purposes of removing a chuck. You will bend/break the pin or damage the corresponding holes in the gear. This has already been done by somebody since the lathe was brought into service here, and now the indexer is damaged. Big frowny face. This pin is for indexing work only, and is not capable of withstanding the force required to crack loose a chuck.
Here is a great method of quickly centering a round workpiece in an independent-jaw chuck:
Here is a video for a slightly different method which would be very accurate:
Cutting tools need to be carefully set to the same height as the lathe's axis of rotation to work correctly. Some people put a dead center in the spindle or tailstock and eyeball their cutting tool to set height. This should be close enough for most turning work, but will need to be dialed in closer for good facing. Here's how I do it:
The distance from the top of the lathe ways to the top edge of a cutting tool set perfectly on center is almost exactly thee inches. This height is easily measured with a caliper's depth rod by resting the end of the caliper shaft on the tool and extending the depth rod straight down to touch the ways. Start with your tool 3.000” above the bed (be picky!) and make a light face cut across a piece of stock. Carefully examine the remaining nubbin at the center to see if you need to move your tool up or down a few thousandths. If you aren't sure, try using a flashlight and a loupe to compare the cutting tool's location relative to the nub. Adjust accordingly and try another very light pass, adjusting until you can face to the middle and leave a perfectly smooth surface. (measure and write down this exact distance once you're getting good results!)
Be careful to take light cuts and feed slowly near the center of the work to minimize the chance of a nubbin walking up onto your cutter; this could break your cutter or damage something else. Remember; this is a lightweight and flexible lathe, and it has a low tolerate for mistakes or abuse. Also, you would rather be slightly low than slightly high; being too high will mean that your cutting tool plows through the nubbin once it reaches the center of the work, whereas being too low means your cutting tool passes (safely, we hope) beneath the nubbin after cutting in a less and less effective manner as it approaches center.
We should be able to determine the exact measurement for this machine that will get you within a thou or so every time, and post it in the wiki here. I just haven't done this yet… -Karl
How do you know what speed is appropriate to run the machine for a given cut? There are several factors that come into play:
- The material being cut (steel, aluminum, brass, delrin, etc.)
- The material of the cutting tool (solid carbide, high speed steel, low-carbon steel, etc.)
- The diameter of the workpiece at the cutting tool (surface speed is what matters; spindle RPM is merely a vehicle to create it)
- The depth of cut you will be taking (light finishing cuts can be done faster than deep roughing cuts)
Many reference charts exist that provide recommended cutting speeds for a given material and cutter. The numbers these charts specify are not the RPM of the workpiece, but the surface speed in feet-per-minute (abbreviated SFPM or just FPM). To create a given SFPM, the material and the cutter must to be moved relative to one another. On a lathe, the cutter is stationary and the work rotates. On a milling machine, the work is stationary and the cutter (usually with multiple cutting edges) rotates. On a shaper, the work is stationary and the cutter reciprocates back and forth. On a planer, the cutter is stationary and the work reciprocates back and forth beneath it.
If you want to know SFPM for a known speed and setup, use this formula:
[FPM] = (3.14 * [RPM] * [Diameter in inches]) / 12
If you want to know the RPM necessary to achieve a specified FPM with a given setup, use this derivation:
[RPM] = (12 * [FPM]) / (3.14 * [diameter])
Here are some suggested starting points for various common materials with high speed steel cutters. Depth of cut, lead angle, material hardness, and various other factors will compound this decision. In general, slower is unlikely to cause problems, but faster is probably a bad idea.
SFPM with HSS tool
|Steel - mild/common||100-125|
|Steel - leaded alloys||200-300|
3/4” aluminum, assuming 250-350 SFPM
(12*250)/(pi*.75) = 1275 rpm (for 250 SFPM)
(12*350)/(pi*.75) = 1782 rpm (for 350 SFPM)
3/4” 1018 steel, assuming 100-125 SFPM
(12*100)/(pi*.75) = 509 rpm (for 100 SFPM)
(12*125)/(pi*.75) = 637 rpm (for 125 SFPM)
Don't forget that Google has a built-in scientific calculator; just punch your formula into the search box as formatted above. (And it knows what you mean when you say pi. Google understands you, unlike Bakers Square.)
Some more detailed good info about selecting feeds and speeds can be found here:
Extremely detailed charts begin on page 1026 of our copy of Machinery's Handbook. These are broken down by different metals/alloys and the tooling type and characteristics. Remember that the tables assume a specific cut with specific tool geometry, and the book's “standard” cut of .125” is a much deeper cut than this lathe could ever hope to make. There are further tables later in the chapter to modify the initial values for different cut depth, lead angle, etc.
Much info is to be added here!
The math of change gears is explained starting on page 56 of this book:
The original power switch was literally on the motor, requiring reaching past the machine. When the current bench was finished, the lathe was mounted on about 1.5” of riser material to improve access beneath the bed for cleaning up, and also providing a logical place for a power switch right below the headstock on the front of the riser block. We used a household light switch in a handy-box that switches an outlet in another handy-box mounted right next to the motor. The motor's rotted power cord was replaced with a new one that is just long enough to reach this outlet. The motor can be unplugged here conveniently for safety while setting up the machine and while it is not in use.
The belt connecting the jack shaft and the spindle cone pulleys has seen better decades. Research indicates that Fenner link belts not only avoid the problem of disassembling the headstock to replace the belt, but also run more smoothly. Other owners of similar lathes have reported good results from replacing this belt with a Fenner. McMaster-Carr carries the proper sized Fenner belting by the foot as part number 6173K36. The belt seems to be a 3/8” wide fractional-horsepower V-belt and measures about 35” to 36” in length.
Update: Karl replaced the main belt with just under 3' of Fenner link belt some time back. It runs great!
How about a shallow cabinet mounted to the wall/bench behind the lathe bench? It could have room for cutting tools, tool holders, chucks, centers, collets, dial indicator goodies, lathe-specific wrenches, change gears, a good caliper, lubrication oil, etc. If it has a solid door, the tooling will stay cleaner and will avoid attracting unsolicited attention/tinkering from passers-by. A shallow drawer beneath the bench would be a great place for stashing chuck keys, wrenches, hex keys, change gears, etc. Drawers catch chips and debris, so perhaps a mad scientist would install a kill switch to disable the motor while the drawer is open? (kidding?)
The existing 4-jaw chuck is great for rough work or irregularly-shaped pieces, but a decent 3-jaw scroll chuck would be amazing for doing precision work. A scroll chuck automatically aligns all of the chuck jaws as it closes, so the work is automatically centered every time to within a few thousandths of an inch. A 4-jaw independent chuck can be dialed in perfectly true (closer than a 3-jaw), but requires an indicator and patience to do so. The 3-jaw is handy for tasks where time is more important than having the work exactly centered, which covers the majority of the work this machine will see.
Update: Karl bought an imported 3-jaw chuck and a 1”-10tpi threaded back plate for about $100. The back plate was turned to create a registration shoulder that matches this chuck on this spindle, and the two were bolted together. The new chuck has two sets of jaws to handle inside and outside clamping over a good range. (note: jaws are numbered and need to be installed in the correct slots to align properly) Overall, it works great!
Karl would like to make a simple radius turning attachment that clamps to the T-slot on the compound. Something that can handle about a 2” diameter ball would be ideal. Here's one approach: