page_title: Machine taper
section_title: R8
hierarchical_section_title: Machine taper / Types / R8
caption_attribution_description: English: cSide and End view of R8 taper collets Nederlands: Spantangen Deutsch: Spannzangen
context_page_description: A machine taper is a system for securing cutting tools or toolholders in the spindle of a machine tool or power tool. A male member of conical form fits into the female socket, which has a matching taper of equal angle.
  Almost all machine tool spindles, and many power tool spindles, have a taper as their primary method of attachment for tools. Even on many drill presses, handheld drills, and lathes, which have chucks, the chuck is attached by a taper. On drills, drill presses, and milling machines, the male member is the tool shank or toolholder shank, and the female socket is integral with the spindle. On lathes, the male may belong to the tool or to the spindle; spindle noses may have male tapers, female tapers, or both.
context_section_description: This taper was designed by Bridgeport Machines, Inc. for use in its milling machines. R8 tapers are not self-holding, so they require a drawbar extending up through the spindle to the top of the machine to prevent loosening when lateral forces are encountered. They are also keyed (see image) to prevent rotation during insertion and removal, although it is the taper that transmits torque in use. The drawbar thread is typically ​⁷⁄₁₆″–20 tpi (UNF). The angle of the cone is 16°51′ (16.85°) with an OD of 1.25″ and a length of ​¹⁵⁄₁₆″. (source, Bridgeport Manufacturer) The diameter of the parallel locating portion is not a "fractional inch" size like the other dimensions and is 0.949″ to 0.9495″.
  Tools with an R8 taper are inserted directly into the machine's spindle. R8 collets are typically used to hold tooling with round shanks, although any shape can be held if the collet has the corresponding shape cut in it. The collets have a precision bore with axial compression slots for holding cutting tools and are threaded for the drawbar. The R8 system is commonly used with collets ranging in size from ​¹⁄₈″ to ​³⁄₄″ in diameter or tool holders with the same or slightly larger diameters. The collets or tool holders are placed directly into the spindle and the drawbar is tightened into the top of the collet or tool holder from above the spindle. Other tools such as drill chucks, fly cutters, indexable insert cutters, etc. may have an R8 taper shank built into or added to the tool.
  The R8 taper is commonly encountered on Bridgeport and similar turret mills from the USA, or on (very common) copies of these mills from elsewhere. The popularity is due in large part to the success of Bridgeport and other mills that were closely modeled after it and produced throughout much of the 20th century.
caption: collets with R8 taper
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