Showing posts with label metalworking. Show all posts
Showing posts with label metalworking. Show all posts

Tuesday, September 6, 2016

Box Jigs for Working With Round Parts



Round part present special challenges in the workshop.  How to we safely machine them on the table saw, drill press, or other machines when their is no flat side to put against the fence and table?  The best solution is usually to build a simple box jig which, as the name implies, is nothing more than a simple box made out of scraps to hold the part.  While the video above uses woodworking examples, box jigs are also handy to hold round or irregularly shaped metal parts for work with machines like mills and shapers.

Basic box jigs come in two types.  Open ended jigs, as shown in the first part of the video, are useful with parts that have one flat face that can be screwed to one of the faces of the box.  They are very especially useful for making cuts in the round part on the table saw or band saw.  Closed end jigs are used with spindles and curved parts which need to be secured from the ends and are especially useful for routing or drilling operations.  While simple versions like the one in the animation at the end of the video usually just use screws to secure the ends of the work, it is also possible to build in lathe-style centers and a shop-built or store-bought indexing head to hold the piece at certain precise angles.  Professional indexing heads are complicated and expensive, but a simple pivoting disk of wood with holes for a pin is often adequate for one-off jobs.  Many furniture makers build simple indexing box jigs to so they can route the mortises in table pedestals to attach the legs.

While they are very simple, box jigs are one of the most useful and common families of jigs in the handyman's workshop.

Tuesday, February 9, 2016

The Turner's Tool Kit



In the latest video I talked about the most important tools for hand turning on the lathe, as well as how to build your own tools.

Edge Tools

If you are just getting started turning your best value will probably be to buy a set of tools, then add to it later, either by purchasing special tools or by making your own. Expect to pay $75 to $100 new for a usable "apprentice grade" set. There are plenty of used tools around, though, since people sell off their original sets as they upgrade. While it is theatrically possible to turn wood with nothing but a single gouge or scraper, a minimalist set of edged tools should include at least the following:
  • Parting Tool
  • Medium Gouge
  • 1/2" Skew
  • Spear Point
  • 1/2" Round Scraper
A more comprehensive set would add:
  • Roughing Gouge
  • Med. Bowl Gouge
  • 1" Skew
If you do a lot of end-grain work (on bowls, rosettes, etc.) or you make patterns for metal casting (which are usually made of MDF, putty, and other man-made materials) you will want to make or buy a couple of other sizes of round and flat scrapers. If you do a lot of small work for models, pens, jewelry, or the like, you might want to get extra small versions of the gouge, skew, and spear-point. And then of course there are a number of specialized tools in the catalogs for particular tasks: combination gouge/skews so you don't have to switch off when you turn spindles, knurling tools to add texture to wood, special tools for undercutting the insides of vases, and a host of others. These tend to be a bit expensive, but they might dollar out if you plan to make dozens or hundreds of the same type of item.

Making your own turning tools

Save your worn out files and other pieces of tool steel. It is relatively easy to make skews and scrapers that are just as good as the store bought kind. You simply grind an old file or a piece of tool steel bar to shape. Then you sharpen it while it is still soft, then temper it with a torch or in a forge. My video this week includes a short animation of how to temper tools. To reiterate the process:
  1. Heat a spot about 2" from the end of the tool to a dull cherry red.
  2. Dip the tool in salt water so that part of the heated area goes under. Salt water is used because if fizzes less when quenching and gives more even heat treating.
  3. Watch the colors in the steel spread out from the part that is still hot towards the now cool end. It helps if you quickly polish the end of the tool with sand paper to remove scale and oxidation.
  4. When the bluish-brown part of the color gets to the cutting edge plunge just the tip of the tool back in the salt water and jiggle it up and down until it stops hissing. The jiggling is to avoid a sharp temper line, which can lead to stress discontinuities in the metal's molecular matrix.
  5. Set the tool aside and let the still-warm parts cool naturally to room temperature. This leads to a hard cutting edge and a shaft that is a little soft, hence less likely to be brittle.
Tempering is something that can be confusing at first but is very easy once you've done it a couple times. In the video I also showed you how to turn handles for your tools. For material I used a piece of maple with a 1/2" section of copper tubing for a ferrule. This is a fairly elementary spindle turning project. The steps are as follows:
  1. Cut a blank of wood slightly oversize. On pieces larger than about 1" you'll usually want to cut off the corners with a table saw or band saw (or a draw knife, if you're feeling old school). This will save turning time.
  2. Mark the centers on each end and make a small dimple with an awl or center punch.
  3. Drill a hole for the tail stock center. The preferred way to do this is to use a specially shaped center drill, mounted in the tail stock, since it will produce holes of exactly the right shape and alignment. When this won't work for some reason it's usually OK to hold the piece in a vice and drill a hole with an electric drill.
  4. Take the spur center off the lathe and drive it into the end of the wood with a hammer or mallet.
  5. If using a solid "dead" style tail stock center, put several drops of oil into the center hole and give it a moment to soak into the end grain.
  6. Mount the work in the lathe and tighten the tail stock ram.
  7. Position the tool rest so that it just clears the corners of the work and the edge is about 1/8" below the centers of the lathe. Rotate the piece by hand to make sure everything clears.
  8. Start the lathe on low speed. Use your biggest, heaviest gouge to rough out a circular shape on the blank. Go until the piece is circular. Exact diameters don't matter at this point as long as it is "big enough".
  9. Find another handle of the same style you are turning and use it as a reference to mark critical points on the turning with a pencil while it spins. Mark end points, points of minimum and maximum diameter, and inflection points where curves flatten out or change.
  10. Increase speed. Use your outside calipers to measure the diameter at each critical point on the model handle then use the parting tool to cut down to this diameter at each of your pencil marks.
  11. Measure the inside diameter of the ferrule with your inside calipers and transfer the measurement to your outside calipers. Cut the space for the ferrule using mostly a medium gouge, but taking the final cuts with a skew.
  12. Remove the piece from the lathe and pound the end into the ferrule with a mallet. Remount the piece in the lathe.
  13. Trim the end with the ferrule so the wood and metal line up perfectly. If the wood is proud of the metal face it down with a skew. It the metal is proud of the wood trim it with a spear point tool.
  14. If the metal of the ferrule is rough, give it a light finish pass with a skew or flat scraper.
  15. Returning to the medium gouge, shape all of the curved and straight surfaces on the handle.
  16. Take a light cut with a sharp skew to fair out the surfaces cut with the gouge.
  17. Move the tool rest out of the way and use sandpaper (up to at least 180 grit) to smooth the turning. If you want the ferrule to be really shiny then wet sand it with 400 grit or higher sandpaper and a few drops of oil.
  18. Switch back to low speed and use a clean lint-free rag to apply a couple coats of lacquer or shellac. The finish will dry almost instantly from the friction and airflow of the spinning lathe.
  19. Once the finish is dry to the touch apply paste wax to the spinning handle, then buff with another clean rag.
  20. Remove the handle from the lathe. Use an electric drill to deepen the hole for the tool tang.
  21. Pad the jaws of your vice and clamp the tool blade in it. Use a mallet to pound on the new handle.
With slight variations this procedure works for the handles of most hand tools, including screwdrivers, chisels, files, and others. With slight modification (using multiple centers to produce an oval cross section) it will also work on things like hammers. If you are just getting started turning I suggest that you gather up all the tools in your garage that have missing, damaged, or ugly handles and turn new handles for them, since it will be a great way to practice your basic spindle turning skills.

Sharpening Tools

Everyone has their own preferences and prejudices when it comes to sharpening but everyone needs to perform the same basic functions: rough grinding to shape new tools and restore damaged edges, honing to sharpen edges, and stropping to polish edges and smooth out wire edges. After experimenting with different systems, including bench grinders and grindstones mounted in the lathe itself, I have settled on my belt sander as my grinder of choice. It's always handy, and it seems easier to control than a round grindstone. Whatever grinder you use, make sure that you only press the tool lightly against the belt or stone and that you cool it immediately when it starts to heat. For honing I normally use a small Arkansas stone with a few drops of whatever oil is within reach. It takes a fair amount of practice to reliably use an oil stone for sharpening but, once you develop the knack, it's still the simplest and most versatile way to sharpen. There are various jigs and guides out there which are supposed to make the process easier, but I've never found one that was worth the bother. One piece of advice I can give you is to sharpen early and often. If you touch up your edges as soon as the begin getting dull then you will be able to go a long time between regrinding. For stropping I favor a SlipStrop, made by Flexcut. This is nothing more than a piece of hardwood with a couple patches of leather glued on and various profiles routed on the back side. You smear it with abrasive (either the yellow stuff from Flexcut or ordinary red rouge) and then pass the edges of your tools against it to polish them and straighten out the microscopic wire edge. The SlipStrop goes for about $15; if you have more time than money you can easily whittle one out of a scrap of hardwood. Masonite (smooth side out) is an acceptable substitute for belt leather and actually seems to work a little better for hard steels like the ones from Solingen or Japan. Scrapers are ground and honed the same way as cutting tools but are normally burnished instead of stropped. This is a process of rubbing a slight "hook" on the scraping edge with a burnishing tool, often a round screwdriver shaft or ratchet extension (especially if it is chromed, since chrome is harder than most steels).

Measuring Tools

Measuring is just as important in turning as in other shop work. For wood turning and ornamental metal turning you will want the following:
  • An accurate 12" ruler
  • Outside calipers
  • Inside calipers
  • Dividers
It's useful to have more than one pair of outside calipers so you can leave a pair set to a particular dimension that you know you will need again. There are several imported sets containing both kinds of calipers and a pair of dividers on the market, which are usually a pretty good value. In the past I have also made my own dividers by jigsawing the legs out of thin plywood or plastic and screwing them together. They aren't nearly as accurate as the store-bought kind, since the amount of "spring" is wrong, but they are good enough for everyday wood turning. For precision metalworking you will need to substantially add to your arsenal of measuring tools. At the minimum you will want:
  • Dial calipers and/or micrometer
  • Dial indicator on magnetic base
  • Small steel square
  • Feeler gauges
  • Combo square with center finder attachment
There naturally work-arounds if you are missing one or all of these. In one of Dave Gingery's books he boasts that he could have built his whole metalworking shop with no precision tools except a $2 set of feeler gauges. On the other hand, cheap import tools get better every year, and things go much faster if you have the right tools for the job.

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.