Hole Blind
Encyclopedia
A blind hole refers to a hole that is ream
ed, drill
ed, or milled
to a specified depth, thus without breaking through to the other side of the workpiece. The etymology is that it is not possible to see through a blind hole. Other types of holes also include through hole
s, and clearance holes. In this instance blind may also refer to any feature that is taken to a specific depth. More specifically referring to internally thread
ed holes (tapped holes).
s. Today many CNC milling machines can run such a thread milling cycle (see a video of such a cut in the "External links" section).
Reamer
A reamer is a metalworking tool used to create an accurate sized hole. The process is called reaming. They may be used as a hand tool or in a machine tool, such as a milling machine or drill press.-Construction:...
ed, drill
Drill
A drill or drill motor is a tool fitted with a cutting tool attachment or driving tool attachment, usually a drill bit or driver bit, used for drilling holes in various materials or fastening various materials together with the use of fasteners. The attachment is gripped by a chuck at one end of...
ed, or milled
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...
to a specified depth, thus without breaking through to the other side of the workpiece. The etymology is that it is not possible to see through a blind hole. Other types of holes also include through hole
Through hole
A through hole refers to a hole that is reamed, drilled, milled etc., completely through the substrate. In other words, a through hole is a hole that goes all the way through something...
s, and clearance holes. In this instance blind may also refer to any feature that is taken to a specific depth. More specifically referring to internally thread
Screw thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...
ed holes (tapped holes).
Threading blind holes
There are three accepted methods of threading blind holes:- Conventional tappingTaps and diesTaps and dies are cutting tools used to create screw threads, which is called threading. A tap is used to cut the female portion of the mating pair . A die is used to cut the male portion of the mating pair . The process of cutting threads using a tap is called tapping, whereas the process using a...
, especially with bottom taps - Single-point threading, where the workpiece is rotated, and a pointed cutting tool is fed into the workpiece at the same rate as the pitch of the internal thread. Single-pointing inside a blind hole, like boring inside one, is inherently more challenging than doing so in a through hole. This was especially true in the era when manual machining was the only method of control. Today, CNCNumerical controlNumerical control refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to controlled manually via handwheels or levers, or mechanically automated via cams alone...
makes these tasks less stressful, but nevertheless still more challenging than with through holes. - Helical interpolation, where the workpiece remains stationary and CNC control moves a milling cutterMilling cutterMilling cutters are cutting tools typically used in milling machines or machining centres . They remove material by their movement within the machine or directly from the cutter's shape .-Features of a milling cutter:Milling cutters come in several shapes and many sizes...
in the correct helical path for a given thread, milling the thread.
Machine tools used for threading blind holes
At least two U.S. tool manufacturers have manufactured tools for thread milling in blind holes: Ingersoll Cutting Tools of Rockford, Illinois, and Tooling Systems of Houston, Texas, who introduced the ThredMil in 1977, a device that milled large internal threads in the blind holes of oil well blowout preventerBlowout preventer
A blowout preventer is a large, specialized valve used to seal, control and monitor oil and gas wells. Blowout preventers were developed to cope with extreme erratic pressures and uncontrolled flow emanating from a well reservoir during drilling. Kicks can lead to a potentially catastrophic...
s. Today many CNC milling machines can run such a thread milling cycle (see a video of such a cut in the "External links" section).