Flat Bottom Drilling

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by Mac Mackenzie

Carbide inserts with flat bottom configurations can lead to lower machining costs


Too often when we are confronted with a different application or even trying to find a better way for an existing one, most of us tend to overlook the possibility of using a drill with features other than a conventional “drill point.”

This is where the flat bottom drill can make life and the application at hand go much easier. When the application demands some form of a flat bottom hole, typically manufacturers have a drill ground with flat cutting edges to produce this flat configuration at the bottom of the hole.

Today some carbide tool manufacturers are seeing a need for a range of standard type drills with flat cutting edges as opposed to 118 to 140° point angles. These flat bottom drills are ideal for producing flat bottom holes. They can also drill parts with angular surfaces, radii, and cross holes with interruptions, as well as aligning pre-drilled holes, round parts, open existing holes, produce a counter-bore, and a variety of other unique applications.

Drills with flat cutting edges can produce a variety of holes, including holes on angular surfaces.Often ignored by many is the fact that with the correct end face configuration on the “flat” drill, it can drill easily to depths exceeding 5 XD and still maintain hole accuracy and positional integrity.

Few carbide tool manufacturers have developed a dual configuration end face, or one that comprises a cutting centre point to maintain tool centrality, combined with flat cutting edges to produce the desired flat bottom. Such a tool variation covers the best of both worlds.

With the development of expert CNC grinding technology, multi-axis tool grinders can be programmed to produce those dual point configurations, which can then be utilized as variable use drilling tools.

The dual configuration end face has been produced on solid carbide tools and has been well accepted in machining to perform operations as previously noted, so where could you expand the development of these tools?

Flat bottom configurations on inserts, such as this one from Yestool Ltd., eliminates regrinding costs.By using the dual face tool on a solid carbide drill, the user would typically have to regrind it using a CNC five axis grinder, which most users don’t typically have in their shops. If the dual face configuration is on an insert, you then use the insert and then discard it, so you don’t need to spend the time or money to regrind it.

The next logical step would then be to have greater versatility by manufacturing the dual configuration end face on a carbide insert, which can be indexed after use. This would reduce the cost and also eliminate the re-grinding process.

Fortunately there are companies who have taken this next step to make the tool totally versatile, not only manufacturing an insert with dual end face at 180°, but also offering other angles on request.

One such company is Yestool Ltd., a drill manufacturer based in Korea, that manufactures flat bottom configurations on inserts. It also has another claim to fame; an indexing drill up to 50 times diameter in depth. SMT

Mac Mackenzie is CEO of Epic Tool

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