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.

1 comment: