Understanding Carbide Tipped Tools
Carbide tipped turning tools are becoming increasingly popular with many of today's wood turners. We'll begin this tutorial by looking at the pros and cons of these tools in comparison to standard high speed steel tools. We will then conclude with details about how you can get better results using these tools by making just a few small adjustments to your methods.
Pros and Cons:
Tool Life -
Carbide-tipped tools have replaceable carbide inserts at the tip of the tool. These small carbide cutterheads are much harder than conventional high speed steel tools, and will hold an edge for longer periods of time. This equates to less down time, as the turner can spend more time at the lathe, and less time at the grinding wheel sharpening tools.
Carbide tipped tools are designed so that they can be rotated (to a sharper section of the tool) or replaced when dull, rather than sharpened. This is a huge benefit to beginners and persons without grinding equipment.
Although carbide will hold an edge for longer periods of time than high speed steel or carbon steel, it can not achieve the same degree of sharpness. A new, unused carbide insert will perform as well as a freshly sharpened steel tool, but only briefly. For fine finishing cuts before sanding, carbide tools (at least in the long term) will not perform as well as other steel tools.
Cutting Ability -
Carbide tools, regardless of shape, are still scrapers. They are designed primarily for scraping the wood's surface away, even if they will perform in other functions such as hollowing or shearing. Learning to use the correct tools (such as bowl gouges, spindle gouges and skews) will greatly improve the quality of your work straight from the tool, and reduce the amount of time that must be devoted to sanding away defects caused during cutting.
Improving Your Results:
Choose the Best Tool -
There are multiple shapes made for the carbide inserts of turning tools. The most common ones are square, slightly rounded square, or round in profile. Square-shaped cutters are best for removing heavy amounts of material quickly, or from cutting flat spots. Slightly rounded square (the sides of the square are ground with a slight radius) cutters can remove material quickly, but can also be used to some degree as a finishing tool. Rounded cutters can remove material nearly as well as the squared-edge types, but are best used for final finishing cuts.
Initial Roughing Cuts -
Throughout the majority of cutting, designate a particular edge of the cutter, or a particular tool to the process. A slightly used cutter will have more of a tendency to tear out end grain as it cuts. This works fine during initial roughing cuts, when the overall quality of the wood's surface is not as important.
Finishing Cuts -
When making finishing cuts, make sure to use the sharpest portion of the tool available. Again, designate a particular edge of the cutter, or a particular tool to this process. A new, or very lightly used cutter will cut more cleanly than a used one, and can remove most tearout or unevenness in the wood's surface. If you've done a good job of roughing out your shape, you should only require a few passes with the tool to clean up the surface and prepare for sanding.