Sharpening


Overview

Jon Magill wrote a really great article where he wrote:

Cutters must be sharp! You will never achieve a reflective cut off the tool, which is always the goal in OT, if your cutter is not sharp. I once read that you can never get a better finish off of your tool than the finish on the tool itself. In other words, unless your cutter has a mirror finish, you cannot expect to produce a mirror finish on your work.

Historical Approach

With regards to sharpening, the method outlined by J.H. Evans in Ornamental Turning in 1903 is

  1. Primary Bevel
    1. Use an oil stone
    2. Use a brass plate with oilstone powder and oil
  2. Secondary / Micro bevel (Evans recommended +3°)
    1. Use a brass plate with oilstone powder and oil
    2. Use a cast iron plate with very fine crocus powder and oil
  3. Debur - very lightly on the back side
    1. Use a cast iron plate with very fine crocus powder and oil

Sharpening Media

Oilstone Powder is very hard to find these days. One can find it occasionally on eBay or other similar sites, but similar products are available from clockmaker suppliers. One which offers such powders is Ernst Westphal.

Fragments of oilstone, when pulverized, sifted and washed, are much in request by mechanicians. This abrasive is generally preferred for grinding together those fittings of mathematical instruments and machinery, which are made wholly or in part of brass or gun metal, for oilstone being softer and more pulverulent than emery, is less liable to become embedded in the metal than emery, which latter is then apt continually to grind, and ultimately damage the accuracy of the fittings of brass works. In modern practice it is usual, however, as far as possible, to discard the grinding together of surfaces, with the view of producing accuracy of form, or precision of contact.
Oilstone powder is preferred to pumice-stone powder for polishing superior brass works, and it is also used by the watchmaker on rubbers of pewter in polishing steel.
From Industrial Recipes by Dr. John Phin, pg. 116-117

Diamond-based lapping compounds should be a very effective alternative.

I have not done any testing with ornamental tools, but products like Kent Grit Diamond Lapping Paste Polishing Compounds should be usable. They are oil based and come in grits from 40 microns, all the way down to 0.25 microns. When used with paper wheels on a grinder, they are very effective for polishing knife edges to be better than razor sharp.


Current Approaches

When sharpening by hand, a Goniostat is often used.

The Accu-Finish machine has been used for years by machinists, and is also used by some ornamental turners. These machines use diamond wheels, or a ceramic lapping wheel with a diamond spray. This is a really great machine, especially as it has a built-in goniostat. But it can be a bit expensive.

I've found the Tormek grinder to meet my needs, though I did have to make some of my own jigs.


Additional pictures of this device


Examples of work produced with this device


Examples of this device in use


Usage Notes


How it works


Notes on making one


More Information

Published Articles

Books and Papers

Web Sites

  • The Sharpening Handbook is intended to also be a good resource for data about sharpening fly cutters. There is information on both round rod cutters, and traditional cutters. This site is especially useful if you are looking to use a Tormek grinder.
  • Ed French created a number of sharpening jigs, and has posted them on GitHub in his folder, SharpeningJigs. Ed posted the STL files, along with the Fusion 360 F3D files. Both the goniostats and the the pucks have a PDF in the folder discussing their use. Ed noted,
    These pucks are designed to be used manually on a flat diamond hone or knife sharpener as well as on lapping machines. The carbide cutters are called split end or half straight. The pucks and goniostats can be 3d printed with 30% infill. The 3dPrintModifier may be used in slicer software to increase infill to 100% around the holes in the pucks.

Presentations

  • This YouTube video shows a demonstration of an Accu-Finish that was given at the 2018 OTI Symposium.

Other

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About this Site

Disclaimer: eMail comments to me at OTBookOfKnowledge @ Gmail.com. The process of woodturning involves the use of tools, machinery and materials which could cause injury or be a health hazard unless proper precautions are taken, including the wearing of appropriate protective equipment.