What may cause reamers to cut oversize?

Built-up edges on the reamer can lead to cutting oversize because a build-up of material along the cutting edges can result in the reamer cutting wider than intended. As chips and debris accumulate on the tool, they can effectively alter the cutting geometry, increasing the diameter of the active cutting surfaces. This alteration in geometry leads to an increase in the size of the hole being reamed.

In contrast, while excessive lubrication, incorrect reamer size, and high feed rates might all impact the cutting process, they do not directly result in the same way that built-up edges can. For instance, excessive lubrication may help in reducing friction but is usually not a direct cause of oversizing. An incorrect reamer size leads to improper initial sizing but doesn't inherently cause a tool to cut oversize beyond its intended size. Similarly, a high feed rate can lead to other issues such as tool wear or damage but wouldn't directly impact the reamer cutting oversized as built-up edges would. Thus, the presence of built-up edges on the reamer is the primary reason for cutting oversize in this context.