What is the Difference between Drilling and Reaming?

Do you know the difference between drilling and reaming? They are both the processing ways and need small power tools, such as handheld tools with drilling bits, rotary power tools etc. Today we will talk about them.

1. Drilling

Generally speaking, drilling is the first process of machining holes in solid materials, and the diameter of the hole is generally less than 80mm. There are two ways to drill holes, one is drill rotation by small rotary tools, and the other is workpiece rotation by handheld electric tools. The errors caused by the above two drilling methods are not the same. In the drilling method with the drill bit rotating, when the drill bit is deflected due to the asymmetry of the cutting edge and insufficient bit rigidity, the center line of the processed hole will be deviated or it is not straight, but the diameter of the hole is basically unchanged. While, in the drilling method of workpiece rotation, it is the opposite. The drilling electric tools commonly used include twist drills, center drills, deep hole drills etc. Among them, the twist drill power tool is often used by people. Of course, the rotary power tool with twisting bits has the same function.

Due to structural constraints, the bending rigidity and torsional rigidity of the drill bit are low, and the centering is not good, the drilling accuracy is low, generally it only reaches IT13 ~ IT11. Then the surface roughness is also large, Ra is generally 50 ~12.5μm. But the metal removal rate of drilling is large, and the cutting efficiency is high. We know that drilling is mainly used to process holes with low quality requirements, such as bolt holes, threaded bottom holes, and oil holes. For holes that require high machining accuracy and surface quality, they should be achieved by reaming, boring or grinding in the subsequent processing.

2. Reaming

Reaming is to use a reaming drill power tool to further process a hole that has been drilled, cast or forged to enlarge the aperture and improve the processing quality of the hole. The reaming process can be used as pre-processing before finishing the drilling hole, or as final machining of less demanding holes. Reamers are similar to twist drills, but have more teeth and no chisel.

Compared with drilling, reaming has the following characteristics:

(1) The reaming drill has a large number of teeth which usually has 3-8 teeth, good guidance, and cutting is relatively stable.

(2) The reaming drill has no chisel edge, and the cutting conditions are good. 

(3) The machining allowance is small, the chip pocket can be made shallower, the drill core can be made thicker, and the strength and rigidity of the cutter body are better. The accuracy of reaming is generally IT11~IT10, and the surface roughness Ra is 12.5~6.3. Reaming is often used to machine holes with a diameter less than Ф100mm. When drilling a hole with a larger diameter (D ≥30mm) by a hand power tool, a small drill bit is often used to pre-drill the hole, and then use the corresponding size reaming drill to ream the hole, which can improve the hole Processing quality and production efficiency.