Chucking reamers are tools used finish a drilled hole to an exact size. Reamers are available in a number of different configurations, some designed for use in machines and others designed for hand operation. Regardless of how the reamer is powered, the configuration is somewhat similar. The reamer consists of no more than a length of tool steel which has been hardened. A certain percentage of the length of the reamer is given over to flutes; the flutes can either be straight, running in the same direction as the shaft, or circular around the diameter.
Some reamers are tapered at the end, this tapering allows for easier insertion of the tool into the pre-drilled hole. In the case of chucking reamers, the diameter is fixed along the entire length of the shaft, this arrangement allows for the entire hole to be reamed to size. Reamers which have a beveled or tapered entry cannot reach the bottom of a blind hole although they can go through a hole which has been drilled completely through the material. The reamer is turned, either by machine or by hand, as it turns it removes just enough material to give the exact diameter hole.
Reamers can be purchased in either a specific size or adjustable. The specific size reamer can only be used for one hole diameter. Fixed size reamers can go as large as two inches and as small as 1/16th inch. During the manufacture of the reamer, the flutes are cut on the shaft, giving the reamer its cutting edges.
An adjustable reamer has tapered slots cut into the shaft. The cutting blades, of which there are two fit into these tapered slots and move up and down. Above and below the blades there are adjusting collars, as one collar is loosened, the opposite collar is tightened. This loosening and tightening process slowly changes the cutting diameter of the reamer. Adjustable reamers are rarely used for standard diameter holes, they are used to ream out odd size holes where a fixed diameter reamer is not available.
Exact diameter holes are required when dowel pins are going to be used. A dowel pin must have an interference fit between the dowel and the hole it is being placed into, the reamer gives and exact measurement and an excellent finish in the hole.
