Learning how to choose the best carbide drill is not as easy as it once was. As you progress from the simple HSS twist drill to the vast array of solid carbide drills, indexable insert drill, indexable head drills, and multi-function carbide drills, the choices can be overwhelming.
Industries such as aerospace, tool-and-die, mold making and mining make extensive use of carbide drills in all their forms. Modern manufacturing would come to a screeching halt if the only drills available were HSS twist drills.
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Factors to consider when choosing a carbide drill
- Application. If you are only drilling a few holes in mild steel and the time requirements are insignificant, HSS would likely work just fine. However, with tougher tool steels, such as H-13, S-7, A-6, D-2 or 420SS, the need for carbide increases dramatically.
- Size of hole. For holes under .5 in solid carbide is required. Solid carbide is available in an almost unlimited size range, while insert drills are much more limited in scope.
- Coolant-thru drills are generally recommended and perform much better than external coolant drills. Regardless of the carbide drill selected, coolant-thru is recommended.
- Interrupted or contoured cuts make hole drilling much more difficult. One typical solution is to mill or spot face, then drill. The solid carbide drill is generally less prone to deflection than an insert drill and is therefore very often the best choice. One exception is the exchangeable tip drill. The geometry of this newer generation of drill enables it to cut much more like solid carbide, without less expense.
- Budget. All the newest and best drills in the world won’t help much if your budget does not allow it. Cutting tools can be very expensive and must be justifiable in order to make sense. There is also a tendency to use more than is necessary when the tool crib is full of nice, shiny new cutting tools.
- Surface finish requirements play a huge role in the selection process. Generally, the solid drills leave a good finish, but for larger holes the inexable inserts can also do an excellent job. There are many factors that go into surface finish, such as machine rigidity, coolant, speeds and feeds, material, and tool holders.
- Size tolerances can make the decision making process much easier. If you need a very precise hole, the solid usually is the way to go, but the newer exchangeable insert drills can do an amazing job in record time
Should you use coated or uncoated carbide drills?
Like nearly everything in the metalworking industry, it depends on many factors. Coated carbide inserts certainly outperform uncoated, plus there are many different types of coatings available.
The Iscar line of solid carbide drills feature a TiAIN coating on a IC08 submicron substrate. This is an effective combination that performs quite well.
The choice of insert coatings can be quite confusing and usually requires the recommendation of an application engineer. For example: you can get inserts with PVD, TiAIN, MTCVD, TiCN, TiN, AI203, TiCICrN, or just uncoated.
Knowing how to choose the right carbide drill is often not an easy task. It takes time and experience to develop your own personal arsenal of tools that meet your unique applications. For this reason, seek out a reputable supplier who has a good R&D department and knowledgeable application engineering staff.
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