REAMERS
What is a reamer?
A reamer is a multi-point cutting tool used for enlarging by finishing previously drilled holes to accurate sizes.
Advantages of 'reaming'
Reaming produces
ØHigh quality surface finish
ØDimensional accuracy to close limits.
Also small holes, which cannot be finished by other processes, can be finished.
Classification of reamers:-
Reamers are classified as a) Hand reamers and b) Machine reamers. (As shown in the below two figs.)
Reaming by using hand reamers is done manually, for which great skill is needed.
Machine reamers are fitted on spindles of machine tools and rotated for reaming.
Machine reamers are provided with Morse taper shanks for holding on machine spindles.
Hand reamers have straight shanks with 'square' at the end, for holding with tap wrenches.
PARTS OF A HAND REAMER:-
The parts of a hand reamer are listed hereunder. Refer to below fig.
Axis
The longitudinal centre line of the reamer.
Body
The portion of the reamer extending from the entering end of the reamer to the commencement.
Recess
The portion of the body which is reduced in diameter below the cutting edges, pilot or guide diameters.
Shank
The portion of the reamer, which is held and driven. It can be parallel or tapered.
Circular land
The cylindrically ground surface adjacent to the cutting edge on the leading edge of the land.
Bevel lead
The bevel lead cutting portion at the entering end of the reamer cutting its way into the hold. It is not provided with a circular land.
Taper lead
The tapered cutting portion at the entering end to facilitate cutting and finishing of the hole. It is not provided with a circular land.
Bevel lead angle
The angle formed by the cutting edges of the bevel lead and the reamer axis.
Taper lead angle
The angle formed by the cutting edges of the taper and the reamer axis.
Terms relating to cutting geometry flutes
The grooves in the body of the reamer to provide cutting edges, to permit the removal of chips, and to allow the cutting fluid to reach the cutting edges. (Fig 5)
Face
The portion of the flute surface adjacent to the cutting edge on which the chip impinges as it is cut from the work. (Fig 5)
Rake angles
The angles in a diametral plane formed by the face and a radial line from the cutting edge. (Fig 6)
Clearance angle
The angles formed by the primary or secondary clearances and the tangent to the periphery of the reamer at the cutting edge. They are called primary clearance angle and secondary clearance angle respectively. (Fig 7)
Heel
The edge formed by the intersection of the surface left by the provision of a secondary clearance and the flute. (Fig 5)
Cutting edge
The edge formed by the intersection of the face and the circular land or the surface left by the provision of primary clearance. (Fig 5)
Helix angle
The angle between the edge and the reamer axis. (Fig 8)
HAND REAMERS
General features of hand reamers
Hand reamers are used to ream holes manually using tap wrenches.
These reamers have a long taper lead.(Figure 2) This allows to start the reamer straight and in alignment with -the hole being reamed.
Fig 1
Most hand reamers are for right hand cutting.
Helical fluted hand reamers have left hand helix. The left hand helix will produce smooth cutting action and finish.
Most reamers, machine or hand, have uneven spacing of teeth. This feature of reamers helps to reduce chattering while reaming. (Fig 3)
TYPES, FEATURES AND FUNCTIONS
Hand reamers with different features are available for meeting different reaming conditions. The commonly used types are listed here under.
Parallel hand reamer with parallel shank (Fig 4)
A reamer which has virtually parallel cutting edges with taper and bevel lead. The body of the reamer is integral with a shank. The shank has the nominal diameter of the cutting edges. One end of the shank is square shaped for tuning it with a tap wrench. Parallel reamers are available with straight and helical flutes. This is the commonly used hand reamer for reaming holes with parallel sides.
Reamers commonly used in workshop produce H8 holes.
Hand reamer with pilot (Fig 5)
For this type of reamer, a portion of the body is cylindrically ground to form a pilot at the entering end. The pilot keeps the reamer concentric with the hole being reamed. (Fig 5)
Socket reamer with parallel shank (Figs 6 and 7)
This reamer has tapered cutting edges to suit metric Morse tapers. The shank is integral with the body, and is square shaped for driving. The flutes are either straight or helical. The socket reamer is used for reaming internal Morse tapered holes.
Taper pin hand reamer (Fig 8)
This reamer has tapered cutting edges for reaming taper holes to suit taper pins. A taper pin reamer is made with a taper pin of 1 in 50. These reamers are available with straight or helical flutes.
Use of straight and helical fluted reamers (Fig 9)
Straight fluted reamers are useful for general reaming work. Helical fluted reamers are particularly suitable for reaming holes with keyway grooves or special lines cut into them. The helical flutes will bridge the gap and reduce binding and chattering.
Material of hand reamers
When the reamers are made as a one-piece construction, high-speed steel is used. When they are made as two-piece construction then the cutting portion is made of high-speed steel while the shank portion is made of carbon steel.
They are butt-welded together before manufacturing.
Specifications of a reamer
To specify a reamer the following data is to be given.
► Type
► Flute
► Shank and
► Size
Example
Hand reamer, Straight flute, Parallel shank of 0 20 mm.
DRILL SIZE FOR REAMING
For reaming with a hand or a machine reamer, the hole drilled should be smaller than the reamer size.
The drilled hole should have sufficient metal for finishing with the reamer. Excessive metal will impose a strain on the cutting edge of the reamer and damage it.
Calculating drill size for reamer
A method generally practiced in workshop is by applying the following formula.
Drill size = Reamed size - (Undersize + Oversize)
Finished size
Finished size is the diameter of the reamer.
Undersize
Undersize is the recommended reduction in size for different ranges of drill diameter. (See Table 1)
TABLE 1 Undersize for reaming
Diameter of ready reamed hole (mm)
|
Undersize of rough bored hole (mm)
|
under 5 . 5......20 21....50 over 50
|
0.1.....0.2 0.2.....0.3 0.3.....0.5 0.5...1
|
Oversize
It is generally considered that a twist drill will make a hole larger than its diameter. The oversize for calculation purposes is taken as 0.05 mm - for all diameters of drills. For light metals the undersize will be chosen 50% larger.
For Obtaining Good Surface Finish
Defects in reaming - Causes and remedies Reamed hole undersize
If a worn out reamer is used, it may result in the reamed hole being undersize. Do not use such reamers.
Always inspect the condition of the reamer before using.
Surface finish rough
The causes may be any one of the following or a combination thereof.
► Incorrect application
► Swarf accumulated in reamer flutes.
► Inadequate flow of coolant.
► Feed rate too fast.
► While reaming apply a steady and slow feed-rate.
► Ensure a copious supply of the coolant.
► Do not turn the reamer in the reverse direction.
COMMENTS