Reamer Basics

Often, we are asked to recommend an appropriate amount of material to be left in a drilled hole for a reamer to efficiently size to a finished diameter.

The general guidelines are <1/4" = .010; ¼" to ½" = .015 and ½" to 1-1/2" = .025 Most end users leave too little stock, thinking it will be easier for the reamer to remove the material, but that does not give the reamer enough material to really cut and will rub or burnish and results in faster wear and poor finish. Speeds should be about 2/3 that of drilling SFM for similar material and feeds 2 to 3 times higher. Perhaps the word "Qualified," in and of itself, truly reflects what we need to know about the tool. "Qualified for Rotation" means that the diameter of the shank and the O.D. of the reamer head run concentric to each other within .0002 (typically .0001) with less than .00005 taper. These characteristics lend themselves to the best angular and radial alignment of the reamer, no matter the application. We can use qualified reamers to great advantage in both rotating and stationary applications. Any time you are utilizing the shank diameter to align the tool in a high tolerance diameter or finish application, the tools should be qualified. If one does not request a qualified reamer, there is potential for angular as well as radial misalignment that you cannot correct at the spindle. This situation is most evident in lathe applications utilizing the "Barber Coleman” up-sharp” style reamer with the pin float hole in a conventional ER style collet chuck. These tools are designed to be run with a pin float holder, the tolerance is put into the cross hole with respect to angular alignment, not in the diameter of the shank. The shanks are ground for clearance in the float. It is important to note that a qualified tool runs equally as well in a pin float holder. An un-qualified tool may or may not run well in an ER collet style holder. When ordering, if you need “Qualified” tolerances, you will need to specify that in your request. Chucking Reamers typically hang out of hydraulic chucks, collet chucks, end mill holders, and even three jaw chucks in some cases. If you are using a hydraulic chuck, they require metric h6 shank tolerance.