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Reamers are tools used for enlarging and finishing diameters of holes to accurate dimensions . A rose reamer cuts on the end and has a chamfer of about 45° on the edge to aid in entering the hole. The fluted chucking reamer, which does more accurate work, is tapered slightly on the end to aid in entering the hole and it cuts on this tapered surface. In general, the reamer follows the hole being reamed. It will change the direction of a hole only slightly. A reamer performs best as a sizing tool when driven by a floating holder that permits it to follow the hole as the reamer is driven through. There are many types of reamers, with straight or spiral flutes, expanding and adjustable blades. They are made to cut different materials, and designed to cut both taper and straight holes.

provision should be made for the reamer to pass through the hole. Blind holes are difficult to ream, and should be undercut at the bottom on the reamed surface.

When a designer specifies a reamed hole it means that:

  1. A drilled hole must be made accurate as to size.
  2. It requires a drill bushing which is removable (known as a slip bushing), and sometimes a reaming bushing added.
  3. The reamer must be available to provide the size in the particular material; and must be able to fit the machine tool.
  4. Gages (usually plug type) must be available to check the hole, for both operator and inspector.
  5. Duplicate sets of reamers should be available, because production must not be delayed when reamers wear and require sharpening.
  6. Wear on the flutes reduces the diameter of the reamer. When the diameter is below the tolerance required, the reamer may be either scrapped or salvaged by grinding for use on smaller diameter holes.

The designer should standardize reamed hole sizes. Hole sizes are based on mating part dimensions.

It is economical to make pins and shafts from cold-rolled and ground stock in order to reduce the amount of turning and grinding to size. Since this material comes in sizes which are to size or under, a series of reamers should be standardized which will ream holes ±0.002 inch or, according to the designers preference for clearance between shaft or pin and hole.

Whenever a surface must be turned or ground on a pin or shaft, the size should be specified so as to offer the proper fit for a standard-sized reamer, ±0.0005 inch. The oversize reamers cost more than standard-sized reamers, but when they wear they can be ground to a standard size, and thus have a double life.

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