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Reamer flute length vs depth of cut. What you need to know.

There seems to be some deal of confusion when it comes to the depth of cut and the flute length of a reamer. In most cases, a machinist who is reaming a deep hole needs additional overall length in the reamer, however, they all-too-often ask for additional flute length as well. “I want a 13” overall length and 6” of flute. My immediate thought every time is simply: Why?”

On a standard carbide tipped reamer only the chamfer portion of the tool is doing the cutting. The main function the flutes play

is to provide a channel for lose chips to flow away from the cutting edge so that the chamfer does not cut the same chips again. Extra long flute lengths add to the costs and manufacturing time. It is not always necessary to have long flute lengths on reamers. In some applications a long flute length will improve performance but in a large majority of applications it does not.  For example you may be reaming a hole that is ½” diameter 4” deep.  The flute length on a standard ½” carbide tipped reamer is 2”.  You don’t need a reamer with 4” of flute to ream this hole.  The 2” flute length is sufficient. In this example the whole 2” of flute should be carbide tipped.  Full flute length carbide is recommended when reaming deeper holes.

The flute length becomes important when the cutting diameter of the reamer you are using is close to the shank diameter of the reamer.  The shank can get in the way of the chips being evacuated. This is an instance where you would want the flute length to be equal to or greater than the depth of the hole you are reaming so the chips can be properly evacuated. Most reamer manufacturers take this into consideration when designing their standard reamers or when they are quoting special reamers.

End-cutting reamers will cut along the chamfer and across the face of the tool, but again the flutes are loose chip channels. Reamers are designed to provide clean and precise holes for tight tolerance parts. By cutting along the chamfer edge only, there is a great deal of control on how much material is to be removed. Generally, reamers are only meant to remove 2-3% of the desired hole size. Many things can affect the performance and outcome of the hole, such as, the number of flutes the reamer has and the speeds and feeds rate that the tool is being operated under. The flute length is important too but too much flute length can result in paying an unnecessarily high price for a reamer,

If you have any questions about reamers and flute lengths (or any other cutting tool questions) feel free to leave us a comment here on our blog or fill out the form on Super Tool’s Contact Us Page.

Chadd Brown
Super Tool, Inc.