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An underreamer is a device used to enlarge the borehole below an existing casing or restriction, during a well drilling operation. It can be positioned either above the drill bit or above a pilot assembly run inside the existing borehole. Numerous designs exist, in sizes varying from a couple of inches to above 40".
A tapered reamer may be used for cleaning burrs from a drilled hole, or to enlarge a hole. The body of the tool tapers to a point. This type of reamer consists of a body which, typically, is up to 1/2 inch in diameter, with a rod cross piece at the large end acting to form a handle.
A bit used to enlarge an existing hole is called a core drill bit. The existing hole may be the result of a core from a casting or a stamped (punched) hole. The name comes from its first use, for drilling out the hole left by a foundry core , a cylinder placed in a mould for a casting that leaves an irregular hole in the product.
The screw is then threaded into the punch and the screw tightened until the punch is drawn completely through the sheet metal. [2] The manual system uses a screw that has a standard hex head or square head and is driven using an allen key or wrench. A manual knockout punch can handle holes from 0.5 to 1.25 in (13 to 32 mm).
Form countersinking, also known as dimpling, is a countersink that is formed into sheet metal to increase the strength of a structure as the countersinks of multiple pieces nest together. There are two processes for producing formed countersinks: coin dimpling and modified radius dimpling . [ 4 ]
It is the most cost effective process of making holes in strip or sheet metal for average to high fabrication. It is able to create multiple shaped holes. Punches and dies are usually fabricated from conventional tool steel or carbides; It creates a burnished region roll-over, and die break on sidewall of the resulting hole. [1] It is a quick ...
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Counterbore Drill Bits – a drill bit used to enlarge existing holes; Countersink Drill Bits – a drill bit to create a wide opening for a screw; High-Speed Drill Bits – these are drill bits made to be very strong and therefore are often used to cut metals; Spade drill Bits – spade-shaped drill bits used primarily to bore holes in softwoods