The Alvord Polk 155-H left-hand helical flute taper pin reamer is a round shank tool made of high-speed steel with no finish or coating, and is most commonly chosen for reaming holes in difficult or long-chipping materials that are intended to receive taper pins. Taper pins are standardized tapered fasteners with one end having a slightly larger diameter than the other end, in order to easily enter a reamed hole and hold itself through friction.
Left-hand helical reamers are useful for interrupted cuts and in through holes. Helical reamers prevent whole flute contact with the leading edge in an interrupted cut, as in a keyway. This prevents damage to the interruption and reamer flute. Left-hand helical style tools also push chips ahead of the tip of the tool, instead of pulling chips out of a hole. Left-hand helical reamers are also useful for reaming through holes, since pushing chips into the hole can cause clogging, which may damage the tool. Helical reamers have a more aggressive rake angle than spiral reamers. This means that while they are both used for similar purposes, helical reamers are intended to be used by a drill press or CNC machine, unlike a spiral reamer, which can be used either by hand or in a machine. Helical reamers cannot easily be used by hand, since the action of the high rake angle means that more force is needed to drive the tool, when used in manually-fed machines they will sometimes push the reamer back up out of the hole.. The round shank (minus a square section on the end) shows the user clearly that this tool is not meant to be used with a tap wrench, i.e. driven by hand. High-speed steel is a general purpose steel for cutting tools and is compatible with many metalworking materials. It is often lower in price than other cutting tool materials.
For reamers in the 155-H series with taper pin size 7/0 to 9 there are three flutes, and for size 10 there are four flutes. Tolerances for machining this reamer series are +.0030 / +.0060 inches.
Reamers are used to finish existing holes. When holes are created using common applications like drilling or punching they often have minute imperfections. Their roundness may be flawed, or their diameter may be slightly smaller than required. Reamers are made to exacting tolerances, so they can correct such errors and create precisely round holes of exacting dimensions. Reaming is often used before tapping screw threads.
Alvord Polk manufactures a broad family of cutting tools, brushes, and tooling components, following ISO 9001 standards for quality and environmental impact of their products. Their offices and manufacturing facilities have been located in the United States since 1881.