Tuesday, January 12, 2016

The Lathe: A Brief History

The history of the lathe is a microcosm for the entire history of technology. The first literary mention of a lathe that I am aware of is in Plato's unfinished Critias, in which Critias describes the island of Atlantis as being perfectly circular with the capital places "as if at the pivot of a lathe" (113d). There is little information on what Hellenistic lathes actually looked like but a certain degree of sophistication would have been required to create some of the mechanisms attributed to Greek inventors. Certainly the Greeks, with their great reverence for geometry, would have seen the potential of a simple tool that makes perfectly circular objects. Simple lathes of some sort (probably based on the Greek models) were around throughout the Roman period--just look at the turned wooden grips on the hilts of late Roman short swords.

In the dark ages everyone got much poorer and tools became simpler. Round objects were more likely to be carved with a draw-knife than turned. Even so, lathes probably never completely went away. By the High Middle Ages wood turners, using simple spring pole lathes, were in business throughout Europe, often unpacking their lathes and setting up in the middle of forests so as to be near a steady source of green wood. Spring pole lathes are deceptively simple. A rope or thong is wrapped around the work. One end is tied to a springy rod (often a handy tree branch) while the other is attached to a pedal, or just tied to the turner's foot. When he steps down the work rotates and he takes a cut. When he raises his foot the spring pole rotates backwards. As primitive as spring-pole lathes are, however, they can potentially do every operation that a modern store-bought electric wood lathe can.

Spring Pole Lathe [Flickr user Mark, CC-BY 2.0]

Spring pole lathes do have one big drawback, though: they you can only cut for half the cycle. This problem was solved with the invention of the treadle lathe, which uses a crank rod attached to the treadle to rotate a flywheel which in turn rotates a drive center through a belt and pulleys. This style of lathe was also easy to connect to an external power source--initially a water wheel, but later a steam engine or electric motor. Many turners actually preferred treadle power, however, because of the fine-grained speed control it gave for delicate operations like threading.

The first treadle lathes were made of wood, as the spring pole lathes had been before. The advent of iron casting, however, allowed for the mass production of lathes in various standard sizes. In the 19th century cast iron treadle lathes were ubiquitous in every kind of shop or factory as well as in home workshops. In his 1869 book on lathe work (definitely recommended reading), Egbert Pomeroy Watson extols the virtues of the lathe as a must-have DIY tool,

There is no family in this country that would not find it economy to have a foot lathe in the house, where the members have mechanical tastes—not necessarily the male members, for ladies use foot lathes, in Europe, with the greatest dexterity. Some of the most beautiful work ever made, was by Miss Holtzapfel, a relative of the celebrated mechanist of the same name. If there are shovels to be mended, the lathe will drill the holes and turn the rivets. If the handle of the saucepan is loose, it will do the same. If scissors or knives want grinding, there is the lathe; if the castors on the sofa break down, there is the lathe; if skates need repairs, either of grinding or of any other kind, there is the lathe. In short, it ought to be as much a part of domestic economy as the sewing machine, for it takes the odd stitches in the mechanical department that save money.

The first lathe I ever used was a Victorian treadle mini-lathe that lived in my Grandfather's basement. He used to use it to make knobs and handles for kitchenware and toys for us grandchildren.
Most of these lathes looked very much like a modern wood lathe, with a simple iron tool rest which was used with various hand tools, but turners used them to work metal as well as wood. The cylinders and threaded parts for the first few generations of steam engines were turned by hand, as were most gun barrels prior to the civil war. Precision metalworking on a simple lathe is absolutely possible!

The mid-19th century saw the next major step in the evolution of the lathe: the engine lathe. These machines used tools clamped in a holder which was attached to a carriage that was moved with hand wheels, allowing for more precision in less time. A further addition of a lead screw (providing a power feed for the carriage) and change gears (for automatic threading in standard pitches) led to the direct ancestors of modern metal lathes. The standard wood lathe and engine lathe have remained relatively unchanged since then and are still a basic part of well-equipped woodworking and metalworking shops, but the late 19th and 20th centuries saw the emergence of a profusion of special purpose lathes optimized for particular jobs: bowl lathes, metal spinning lathes, brake drum lathes, pipe machines (a lathe designed to cut and thread pipe on job sites), and many others. In the second half of the 20th century the focus was on automation. Production wood lathes gained duplicator attachments to rapidly copy table legs and similar pieces by following a template. Metal lathes gained turrets which held several different tools for rapid selection. With the advent of CNC technology the turret lathe became fully computer controlled.

At the same time that production lathe technology was heading towards specialization and automation, however, there was a growing interest in simple lathe designs which could be built cheaply and used for a wide variety of tasks. One of the first to publicize this sort of lathe was hand tool woodworking guru Roy Underhill, who has built and demonstrated several simple foot-powered lathes on his PBS show The Woodwright's Shop and currently teaches a class in how to build your own spring-pole lathe. Prior to becoming a TV personality Roy toured the craft-fair circuit with a treadle lathe built mostly out of construction lumber, doing spindle turning while playing the harmonica. All of his lathes are built out of wood with only a few metal parts. In the 1980's Dave Gingery came on the scene with a series of books about how to build a machine shop from scratch. The core of his program was a simple but versatile engine lathe built from pot metal and aluminum castings. Many thousands of hobbyists have since built and used Gingery lathes. More recently, there has been an upsurge in interest in a WW I-era engine lathe design by Lucien Yeoman which was created to rapidly tool up munitions factories. Yeoman lathes are built mostly out of concrete with pipe ways. They require no foundry work and only minor welding. Yeoman lathes can typically be scaled up larger than Gingery lathes because the latter are limited by the amount of metal you can heat in a single pour. My own lathe design incorporates elements from the Underhill, Gingery, and Yeoman designs, and was largely dictated by the tools and materials I happened to have on hand. I don't have a foundry or a welder, but I did have a box of old bicycle parts and plenty of wood. Also, I have pretty complete sets of woodworking and bicycle tools (I'm a journeyman in both those trades) but only basic metalworking tools. So I built a lathe mostly out of wood, like Roy Underhill, but with pipe ways like Yeoman. The headstock bearings and spindle are a bicycle bottom bracket and I used bicycle quick-release levers to lock down the tool rest and tailstock. Gingery's book was constantly at hand as I designed, machined, and assembled the various pieces.

Roy Underhill with one of his lathes

A Yeoman Lathe [courtesy of opensourcemachinetools.org]

Since completing the Handy Lathe six month ago I have used it for numerous projects in wood, plastic, and metal, and it works pretty well. The biggest problem I have is that the headstock spindle occasionally gets bent and I have to realign it (a fairly easy process involving a surface gauge and a big Crescent wrench. I am in the process of setting up a small foundry which will allow me to sand-cast parts. When it is done I plan to build a Gingery-stylr carriage and tool-holder to make the Handy Lathe into a true engine lathe. I also plan to turn a beefier spindle as soon as I find a big enough chunk of steel. My long term plan is to use the Handy Lathe to machine the parts for my dream lathe, the Handy Lathe Mk. II, which will be a full size machine with a geared transmission. For now, though, the Mk. I suits my needs quite nicely and I also think it would be a good first machine for someone who wanted to learn turning.

The Handy Lathe

Tuesday, January 5, 2016

Pipe-End Grinding Jig

This season of the show I'm trying to focus more on workshop skills, and one of the most basic workshop skills is designing and building jigs and fixtures. In a small shop you almost never have specialized machines to do particular jobs. But as long as you have a few basic power tools, and some ingenuity, you can usually build jigs to do any job you need. For example, the other day I was building something out of metal, and I had a problem. I needed to socket a piece of pipe into a hole, but the end of the pipe was bigger than my biggest drill bit. I could have ground the end of the pipe down by hand, but this was a precision job and it would have been tough to keep everything straight and circular. I would have had the same problem if I tried to file out the hole bigger. Instead, I spent about 20 minutes and created what was essentially a new power tool to do the job, a grinder that produces tendons on the ends of pipe or round stock.

You may never have the same problem, but I thought it would be a good example of a jig with moving parts that might give you some useful ideas.

Step by Step

  1. Find a piece of pipe that has approximately the same inside diameter as the outside diameter you need to grind. If you don't have a pipe vice, grind some flats on the end of the pipe so a regular machinist's vice will grip it securely.
  2. Use a hand ream to smooth the bore of the pipe and enlarge it to a couple thousandths of an inch bigger than the finished diameter of the tendon you need to cut. The ream I use is made for bicycle seat tubes but I use if for all sorts of jobs. Be sure to use plenty of cutting oil and take many light cuts.
  3. Find a piece of steel strap to hold the pipe. I broke this one off the back of an electrical box.
  4. Use a table saw to cut the v-shaped notch where the jig hits the pipe.
  5. Use a table saw to round the corners on the upper piece of wood and to rough out the hinge. You could do all of this with a hand saw, the table saw is just faster.
  6. Use bench chisels to clean up the hinge.
  7. Drill a hole and insert a hinge bolt.
  8. Put a couple screws through the wood to reinforce it at likely splitting points (not shown in video).
  9. Attach the pipe, using screws to hold on the strap.
  10. Attach the grinder to the jig with some 12-gauge electrical wire. You can also run a screw through the wood to engage one of the holes in the grinder (not shown in video).
  11. Build and install the cut depth adjustment screw. If you decide to make a wing-screw, follow these steps:
    1. Find a wing-nut with an inside diameter slightly smaller than the outside diameter of the screw head.
    2. Turn the screw head to the thread-crest diameter of the threads on the wing-nut. If you don't have a lathe you can chuck the screw in a drill and turn it with a file.
    3. Use a die to thread the screw head then screw on the wing-nut.
    4. Solder the two pieces together.

    Another method, which doesn't require threading, is to clip a dime in half and solder one of the halves into the screwdriver slot on (flat-head) pan head screw.
  12. Blunt the end of the cut-depth adjustment screw and add another screw where it contacts the upper piece of wood. This will keep it from digging into the wood.
  13. Clamp the jig in your vice.

Using the Jig

Slowly rotate the pipe you're grinding against the grinding wheel as you slide it into the other pipe. You get smoother action if you grease the inside of the larger pipe. PRO TIP: Set up a "junk yard" for all your old one-off jigs. When you build a new jig it's often faster to cannibalize old ones for parts than to start from scratch.