Turning with Sharp Tools - Series Introduction
Over the next several months, we're going to cover some of the finer details of sharpening and maintaining wood turning tools. We'll be covering a variety of tools, one at a time, to explain how to properly sharpen each one to get the best results from your tools. The first few tutorials are going to cover how to properly identify tools which are dull or incorrectly sharpened. After that, we'll begin to cover proper grinding of a variety of tools, one at a time, in great detail.
This month, let's take a look at how to visually inspect the cutting edge of your turning tools. We'll learn how to properly identify a dulled edge, and what to look for to ensure your tools are ground properly as well.
Visual Inspection of Lathe Cutting Tool Edges -
Look for Bluing of the Tool Steel
When tools are sharpened to quickly (which produces excessive heat), the steel can become blued, as shown in the photo to the left directly above. Once the steel has been blued, the temper (hardness) of the steel is lost, and the cutting edge will dull very rapidly. If your tool has become blued, you will need to regrind the cutting edge until the bluing has been removed. Do this by grinding more slowly, and pausing to allow the tool to cool somewhat before continuing with sharpening. This is particularly important if you are using a high speed grinder (3500 RPM) instead of a low speed grinder (1750 RPM), which should be used for tool sharpening.
Check Cutting Edge for Sharpness -
In order to visually inspect the sharpness of your tool's cutting edge, you will need to hold it up under good lighting. In the photo above, you should be able to notice two different areas which reflect light differently. The sharp area in the right side of the photo shows an edge which disappears into an indistinguishable thin line at the intersection of the top edge of the tool and the ground edge at the front. This is what you want to see. In the dull side shown at left in the photo, you will notice that there is a thin line which is reflecting light differently at this same intersection between the two faces of the tool. This is where the cutting edge of the tool has been slightly rounded over and is no longer sharp. Learning to visually identify a dulled edge is quite simple using this method...just be sure to hold it up under a bright light, and vary the angle of the tool under the light to see if you can spot the tell-tale reflection of a dulled tool edge.
Final Thoughts -
The final visual inspection that should be performed is checking the quality of the grinding for evenness across the tool. Is the edge of your skew or scraper straight and uniform, or are there bumps or wavy areas? Is the nose of your bowl/spindle gouge a smooth curve, or is it uneven in spots? If your tools have become misshapen during grinding, it is wise to go back to the grinder, and regrind your tools properly. In the end, it will make turning much easier once you become experienced in properly sharpening your tools!