Grooving can be bumpy: Turning Performance

Cutting grooves is one of the more challenging turning operations performed by machinists. Grooving tools are often thin and fragile. They have three sides in contact with a part, and chips can be difficult to extract.

After many scrapped parts and broken tools, I learned important lessons about grooving.

My first turning experiences were on a 1947 Monarch 10EE lathe, which was completely manual, as you probably would guess. After a little instruction and some practice, most people can make a turning tool that cuts. I learned to grind my own turning tools and became fairly good at offhand grinding. However, grinding usable grooving tools is tough. It takes lots of practice to achieve fine results. I could make a usable grooving tool in a pinch, but the process was slow and cumbersome.Lessons

Used for internal grooves, this standard lathe grooving tool (right) is from a catalog. Mitsubishi Hitachi Power Systems Americas has used the tool in milling machines for hot jobs. Image courtesy of C. Tate

Lesson one. Buy a good grooving tool from a company that knows what it is doing. For manual machines, that frequently means purchasing a parting blade. Parting blades are made of high-speed steel and ground with proper clearances, so a tool does not rub the sides, which is the most common problem with hand-ground tools. Parting blades are available in many sizes and can be modified easily for special purposes.

Unfortunately, HSS tools do not always work well with hard or abrasive materials, which I discovered while machining cast-iron parts. Carbide grooving tools become a necessity with difficult-to-machine materials and bring their own challenges, especially on conventional machines. Carbide is significantly harder and more wear-resistant than HSS but very brittle and not as forgiving. Carbide tends to chip and break if not used properly. I learned this while feeding a carbide grooving tool by hand on cast-iron parts. That is lesson two.

Lesson two. Use a light feed rate, and let the machine feed the tool. Only hand-feed at the end if necessary.

Lesson three. When cutting grooves on a lathe, make sure that the grooving tool is on center or slightly below. Turning and facing tools can tolerate being above centerline, and small errors are often unnoticeable. But a grooving tool above centerline provides hours of aggravation as the part tries to climb up on the tool, the cutting edge continually is rubbed off or half a day is spent gingerly coaxing a piece of broken tool out of a shaft that is 99% complete.