What Is a Drill-Reamer?
A drill-reamer is a tool that can perform drilling and ream at the same time.
Typically, reaming is after drilling the pre-drilled hole. (Reaming: Finishing process to adjust the diameter accuracy and surface roughness of the hole.) Therefore, the same hole must be reamed twice.
However, with a drill-reamer, reaming can be performed simultaneously in a single operation, thus drastically reducing machining time.
Generally, the tip of the drill-reamer is in the shape of a drill. The center of the cutting edge to the base of the reamer is in the shape of a reamer rather than a drill.
Uses of Drill-Reamers
Drill-reamers are for machining that require hole diameter accuracy and surface roughness.
Using a drill-reamer for drilling holes that do not require bolt threading or positioning is unnecessary. Standard drilling is sufficient.
Then, in what case is a drill-reamer used? Let’s take a die as an example.
The lifeline of a die is the die and punch. The clearance between the die and punch must be adjusted in hundredths of a percent so that they are installed in the same position no matter how many times they are reassembled. This is where the positioning pin comes in. A drill-reamer is used for the hole to fit this locating pin. If the hole is inaccurate, the positioning pin will be misaligned, and the punch and die will be out of alignment. In the worst case, this can lead to breakage.
Thus, drill-reamers are for drilling holes that require precise positioning and when machining to fit tolerances of precision parts.
Principle of Drill-Reamers
Drill-reamers were developed to improve work efficiency by simultaneously drilling the pre-drilled hole and reaming the hole diameter by shaving the sides of the pre-drilled hole.
The drill-reamer has cutting edges for both drilling and reaming. Therefore, drilling and finishing can be performed in a single machining operation.
The cutting-edge shape of a drill-reamer is shown below.
- Cutting edge for drilling at the tip (about 10 to 30 mm)
- Drilling cutting edge (corner to back) reaming cutting edge
The reamer is behind the corner of the cutting edge for drilling. The reamer allowance is set at 0.1 to 0.5 mm.
For example, in the case of a drill-reamer with a finishing dimension of 8 mm, nominal dimensions are 8 mm: drill diameter 7.7 mm, reamer diameter 8 mm, drill blade length 22 mm, and overall blade length 80 mm.
The bite angle that switches to the cutting edge for reaming is often set in the range of 15° to 45°. In addition, chips are cut by the nick or breaker, allowing for smooth chip evacuation and improving the accuracy of reaming.
High-speed steel is mainly used for drill-reamers. Some have a TiCN coating on the cutting edge for superior durability.