Reamer
A reamer is a tool for enlarging holes and is used in metalworking. It may be used as a hand tool or may have a specialized drive end. For production machine tools the drive will usually be a standard taper. For hand tools the drive will usually be a square drive, intended for use with the same type of wrench used to turn a tap for the cutting of threads.
A reamer consists of a set of parallel cutting edges along the length of a cylindrical body. Each cutting edge is ground at a slight angle and with a slight undercut below the cutting edge. Reamers must combine both hardness in the cutting edges, for long life, and toughness, so that tool does not fail under the normal forces of use. They should only be used to remove small amounts of material, this ensures a long life for the reamer and a superior finish to the hole.
The spiral may be clockwise or counter-clockwise depending on usage, eg:- a tapered hand reamer with a clockwise spiral will tend to self feed as it is used, possibly leading to a wedging action and consequent breakage, an anti clockwise spiral is therefore preferred.
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Adjustable hand reamer
ReamerAdjustableHand.jpg
An adjustable hand reamer can cover a small range of sizes, they are generally referenced by a letter which equates to a size range. The disposable blades slide along a tapered groove, the act of respectively tightening and loosening the restraining nuts at each end, varies the size that may be cut. The absence of any spiral in the flutes restricts them to light usage (minimal material removal per setting) as they have a tendency to chatter, they are also restricted to usage in unbroken holes. If a hole has an axial split along it, such as a split bush or a clamping hole, each straight tooth will in turn drop into the gap causing the other teeth to retract from their cutting position, this also gives rise to chatter marks and defeats the purpose of using the reamer to size a hole.
Straight reamer (precision)
A straight reamer is used to make only a minor enlargement to a hole. The entry end of the reamer will have a slight taper, the length of which will depend on its type, this produces a self centering action as it enters the raw hole. The larger proportion of the length will be of a constant diameter.
Reamed holes are used to create holes of precise circularity and size. This will allow the force fitting of locating pins, which need not be otherwise retained in the body holding them. Other holes, reamed slightly larger in other parts, will fit these pins accurately, but not so tightly as to make disassembly difficult. This type of alignment is common in the joining of split crankcase halves such as are used in motorcycle motors and boxer type engines. After joining the halves, the assembled case may then be line bored (using what is in effect a large diameter reamer), and then disassembled for placement of bearings and other parts. Another use of reamed holes is to receive a specialized bolt that has an unthreaded shoulder. This type of bolt is commonly used to replace hot peened rivets during the seismic retrofit of structures.
Hand reamer
A hand reamer has a longer taper or lead in at the front than a machine reamer. This is to compensate for the difficulty of starting a hole by hand power alone, it also allows the reamer to start straight and reduce the risk of breakage. The flutes may be straight or spiral.
Machine reamer
ReamerMachineSpiral.jpg
A machine reamer only has a very slight lead in. Because the reamer and work piece are pre-aligned by the machine there is no risk of it wandering off-course, in addition the constant cutting force that can be applied by the machine ensures that it starts cutting immediately. Spiral flutes are essential on a machine reamer to clear the swarf automatically.
Rose reamer
Shell reamer
Tapered reamer (precision)
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A precision tapered reamer is used to make a tapered hole to later receive a tapered pin. A taper pin is a self tightening device due to the slow angle of the taper, they may be driven into the tapered hole such that removal can only be done with a hammer and punch. They are sized by a number sequence (eg:- No.4 reamer would use No.4 taper pins). Such precision joins are used in aircraft assembly and are frequently used to join the two or more wing sections used in a sailplane. These may be re-reamed one or more times during the aircraft's useful life, with an appropriately oversized pin replacing the previous pin.
Morse taper reamer
ReamerMorseTaper3.jpg
A morse taper reamer is used to manually finish morse taper sleeves. These sleeves are a tool used to hold machine cutting tools or holders in the spindles of machines such as a drill or milling machine. The reamer shown is a finishing reamer, a roughing reamer would have serations along the flutes to break up the thicker chips produced by the heavier cutting action used for it.
Tapered reamer (non-precision)
A tapered reamer may be used 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. It is especially useful for working softer metals such as aluminum, copper, and mild steel.