An Introduction to Reamers & CNC Reaming

From In the Loupe on

Most machinists are familiar with CNC drilling, but did you know that the common practice for holemaking is to always use a reamer? When done correctly, reaming can be a fast and highly accurate operation that results in precision holes.

Critical Reamer Geometries


By examining the above image of a Harvey Tool Miniature Reamer and its critical dimensions, we can better understand the functionality of this useful tool.

D1 is the reamer diameter. This is the diameter of the specific size intended for your hole.

D2 is the shank diameter. These oversized, but common shank sizes help to maintain tool strength, stiffness and accuracy. It is also important to note that these shanks have an h6 tolerance, crucial for high precision tool holders such as heat shrink collets.

L1 is the overall length of the tool. This dimension is important to consider when touching the tool off or estimating its hang out. It’s always best practice to minimize tool hang out as much as possible.

L2 is the margin length of the tool. As defined in the Machinist’s Handbook, the margin is the unrelieved part of the periphery of the land adjacent to the cutting edge.

L3 is the overall reach of the reamer. This lets the machinist know how deep the reamer can get into a hole.

L4 is the chamfer length.The chamfer is the cutting portion of the reamer – the part of the tool that is actually removing material.

Read the rest of this great article on

Share this post

Leave a Reply

Your email address will not be published. Required fields are marked *