The hole drilled by the drilling operation is rough from the inside and not as accurate as required. Also for the perfect fitting, accuracy and finishing of the hole is most important. Therefore, a process is required which gives a fine finishing surface to the hole and makes the hole more accurate that process is known as reaming. In this chapter, we are going to study the reamer, its types, and uses.
Reamer
A reamer is a multi-point cutting tool used for enlarging the holes by finishing previously drilled holes to accurate sizes.
Reamer cuts the metal in a very small amount from 0.02 mm to 0.15 mm. This value is also known as reaming allowance. At the time of drilling or boring, a reaming allowance is provided. Sometimes, reaming is performed in two steps. In the first step, rough reaming is done and in the second step, finished reaming is done.
Construction of Reamer
It is made up of high-carbon steel, high-speed steel, or alloy steel. It has many cutting edges. A reamer can be made up of three parts. All of these are discussed here.
- Body
- Shank
- Chamfer
1. Body
The part that contains the cutting edge is known as the body of reamer. It is the main part of the reamer.
The part between the flutes is known as land. Margin is provided behind the land, which is present from the chamfer to the back end of the flute. On land, body clearance is provided after the margin.
2. Shank
It is the upper part of a reamer and present above the body. This portion of the reamer is held and driven with the help of a machine or by hand. Some of the reamer heads are square. The square head is rotated with the help of a tap wrench,
3. Chamfer
Chamfer is provided at the lower portion of the body at a specific angle so that body clearance remains behind the chamfer cutting edge.
Types of Reamers
Beamers are divided into two types.
- Hand reamer
- Machine reamer
1. Hand Reamer
A square tang is made on its shank. This tang is easily held in a wrench or handle for movement by hand, Its body has spiral or straight grooves and a taper flute from the backside so that the reamer during cutting should not fastened. According to the Wars of Reamer, it is of different types
(i)Parallel Hand Beamer
The body of the parallel hand reamer is cylindrical and has a parallel flute. These flutes are either straight or helical and a chamfer is provided at the lower part so that it can easily enter in a drill hole. It can cut the metal from 0.05 to 0.125 mm.
(ii) Taper Hand Reamer
A Taper hand reamer is used to taper the drill hole. It has either a straight or helical flute on its body. It is normally available in pairs (i.c., one for rough reaming and the second for fine reaming) to obtain the finished product.
(iii) Adjustable Hand Reamer
In this reamer, slots are made on the tapered body of the reamer, in which cutting blades are slides and the cutting edges are parallel to one another. Cutting blades present between the two nuts tighten in the thread present on the body of the reamer.
(iii)Adjustable hand reamer
Its size can be changed up to 0.8 mm. Due to the adjustment of size, it is known as an adjustable reamer. It is mostly used for repair work.
(iv) Taper Pin Hand Reamer
It is used in places where a taper pin is used to fit in a hole. Its body has a standard taper of about 20 mm. It has both straight and helical flutes.Â
(v) Expansion Hand Reamer
The body of these reamers is split and has a tapered hole in the lower head, in which threads are cut. A plug is fitted in this thread and when the plug is tightened the body of the reamer expands. Expansion reamers are used for reaming of bigger size holes.
(vi) Pilot Hand Reamer
In the pilot hand reamer, the pilot is used to guide the reamer, to be straight in the hole. For this, a pilot is made on an end of the body which is the same as the size of the hole.
2. Machine Reamer
As the name indicates, the reamers that are used with the help of a machine is known as machine reamers. These reamers are mainly of taper shank of flat tang. These flat tangs are fixed in the spindle of the machine and reaming is done. It is of the following types
(i) Rose Machine Reamer
In this reamer, the chamfer is 45°. Due to this cutting, the reaming operation is performed only by the lower portion of a reamer. Therefore, no clearance is given on land. It is used beforehand reaming for rough reaming.
(ii) Jig Machine Reamer
When the guide bush is fitted with a jig plate, it guides the reaming operation of a reamer, and the machine with a jig plate is known as a jig reamer. The shank and body up to the middle part are made in a cylindrical shape of the same diameter as in a guide bush.
At the time of reaming, this surface is inside the guide bush and gives the accurate location of the reamer. It is used in mass production.
(iii) Flute Machine Reamer
The number of flutes present on this type of reamer is more, it also has land, margin, and clearance body. This type of reamer gives a more accurate and finished surface.
(iv) Shell Machine Reamer
It is like a rose or flute machine reamer except that it is hollow from the inside and can be used after fixing in an arbor. Arbor is designed in straight or taper as per requirement. The main advantage of this reamer is that its arbor can be used with different sizes of reamer.
The shell machine reamer is used for reaming the bigger holes.
(v) Adjustable Machine Reamer
The working of an adjustable machine reamer is the same as that of an adjustable hand reamer.
The adjusting nut is fitted to adjust the size of the reaming, expansion blades are expanded with the help of the adjusting nut and then fit into the spindle of the machine.
Specifications of Reamer
At the time of purchasing the reamer or selecting it for any process, the following four things must be remembered.
(i) Type of reamer Hand reamer or machine reamer.
(ii) Type of shank Taper shank or parallel shank.
(iii) Type of flute Straight flute or helical flute.
(iv) Size of reamer Depending on the diameter of the hole, the size of the reamer is selected.
e.g., Machine reamer of shell-type taper shank of 12 mm.
Reamer Drill Size
The formula given below is applied for Calculating the reamer drill size.
            RDS = RS – (Undersize + oversize)Â
where, RDS = Reamer Drill SizeÂ
              RS = Reamer Size.
Undersize
It is the recommended reduction in size as per the table given below.
Undersize for Reaming
| SL No | Diameter of Teamed Hole | Undersize of Rough Bored Hole |
| 01 | Upto 5 mm | 0.1 mm to 0.2 mm |
| 02 | 5 to 20 mm | 0.2 to 0.3 mm |
| 03 | 21 to 50 mm | 0.3 to 0.5 mm |
| 04 | Above 50 mm | 0.5 to 1.0 mm |
For light metals, the undersize will be chosen 50% larger.
Oversize
Generally, a drill makes a hole larger than its diameter even when the drill is grounded correctly. For calculation purposes, the oversize is considered as 0.05 mm for all diameters of drills.
Example 1 A reamed hole of 12 mm diameter is to be made on a mild steel job. What will be the reamer drill size?
Solution Given, reamer size = 12 mm and oversize = 0.05 mmÂ
                         and undersize = 0.2 mm from the table
  Now,               RDS = RS- (undersize + oversize)Â
                                                = 12 mm-(0.2 mm + 0.05 mm)Â
                                      RDS = 11.75 mm
Comparison between Reaming and Drilling
| SL No | Reaming | Drilling |
| 01 | It is not used for making holes. | It is used for making holes in solid materials. |
| 02 | With its use, the diameter of the hole can be increased slightly. | An increase in diameter is not possible. |
| 03 | The hole can be tapered. | Tapering is not possible. |
| 04 | It makes the hole accurate. | It is not so accurate. |
| 05 | The bottom of the hole is better cleaned. | Its bottom is normally cleaned. |
| 06 | The proper size of the hole is possible with it. | The proper standard size of the hole is not possible. |
As we discussed earlier reaming is a process of making a hole more accurate and fine finish, it can be done alone either by hand or using the machine.
Reaming by Hand
The following points should be noted while reaming by hand.
(i) Clamp the job in the vice firmly.
(ii) Check the reamer hole size which should be about 3% less than the reamer size.
(iii) Place the reamer into the hole and check its perpendicular position.
(iv) Move the reamer clockwise with light pressure.
(v) Use proper coolant while reaming.
(vi) After completion of reaming, clean the reamer and job then place the reamer in its place.
Reaming by Machine
The following points should be noted when reaming by machine.
(i) Clamp the job on the table of the machine firmly.
(ii) Hold the reamer with the aid of a holder or adapter sleeve.
(iii) Be sure the reamer runs correctly and take care in starting the cut.
(iv) Bring the reamer to the edge of the hole before starting and feed it carefully.
(v) Use proper coolant while reaming.
(vi) Don’t allow the reamer to chatter, it will affect the smoothness of the hole.
(vii) Use proper speed. It is usually somewhat less than for drilling to avoid any tendency to overheat and ruin the cutting edge.
(viii) The feed should not be crowded.
(ix) After completion of reaming clean the machine, reamer, and job.
Precautions while using Reamers
(i) Reamers should be placed into the hole in a perpendicular position.
(ii) Never turn the reamer backward or anti-clockwise.
(iii) Don’t try to start a reamer on an uneven surface.
(iv) Use proper lubrication while reaming.
(v) Never use a blunt reamer for reaming.
(vi) For reaming a blind hole, move the reamer upward from time to time.
(vii) Use proper coolant while reaming.
Countersinking, counterboring, and spot-facing are also processes that are performed to change the dimensions of the drill holes just like the reaming process. So, let us discuss all of these one by one.
Countersinking
Countersinking is an operation of bevelling (reducing a square edge to a sloping edge) the end of a drilled hole. The tool used for the counter-sinking process is called a countersink.
Countersinking is carried out to provide a space for the head of the countersink screw so that it is flush with the surface after fixing It also deburr a hole after drilling and chamfer the ends of the hole for thread cutting and other machining processes.
The most commonly used countersinks have multiple cutting edges and are available in taper and straight shank. For countersinking, small diameter holes and special countersinks with two or one flute are used. This will reduce the vibration while cutting.
Countersink Hole Sizes
The countersink holes according to Indian Standard IS: 3406 (Part 1) 1986 are of four types.
- Type A
- Type B
- Type C
- Type E
Type A for countersink hole size
Type A is suitable for slotted countersink head screws cross recessed and slotted raised countersink head screws The various features of dimensions of type A countersink holes and the method of designation are given in Table 1
A countersink (YDISA with a clearance hole of fine (1) series and having nominal size 10 shall be represented as countersink A/10-IS: 3406.
Table I
Dimensions and Designation of Countersink-Type A According to IS: 3406 (Part 1) 1986
| For Nominal Size | Medium Series (m) d1 H13 | Medium Series (m) d2H13 | Medium Series (m) t13 | Fine Series (f) d1 H12 | Fine Series (f) d3H12 | Fine Series (f) t13 | Fine Series (f) t2+ 0.10 |
| 1 | 1.2 | 2.4 | 0.6 | 1.1 | 2 | 0.7 | 0.2 |
| 1.2 | 1.4 | 2.8 | 0.7 | 1.3 | 2.5 | 0.8 | 0.15 |
| (1.4) | 1.6 | 3.3 | 0.8 | 1.5 | 2.8 | 0.9 | 0.15 |
| 1.6 | 1.8 | 3.7 | 0.9 | 1.7 | 3.3 | 1 | 0.2 |
| (1.8) | 2.1 | 4.1 | 1 | 2 | 3.8 | 1.2 | 0.2 |
| 2 | 2.4 | 4.6 | 1.1 | 2.2 | 4.3 | 1.2 | 0.15 |
| 2.5 | 2.9 | 5.7 | 1.4 | 2.7 | 5 | 1.5 | 0.35 |
| 3 | 3.4 | 6.5 | 1.6 | 3.2 | 6 | 1.7 | 0.25 |
| 3.5 | 3.9 | 7.6 | 1.9 | 3.7 | 7 | 2 | 0.3 |
| 4 | 4.5 | 8.6 | 2.1 | 4.3 | 8 | 2.2 | 0.3 |
| 4.5 | 5 | 9.5 | 2.3 | 4.8 | 9 | 2.4 | 0.3 |
| 5 | 5.5 | 10.4 | 2.5 | 5.3 | 10 | 2.6 | 0.2 |
| 6 | 6.6 | 12.4 | 2.9 | 6.4 | 11.5 | 3 | 0.45 |
| 8 | 9 | 16.4 | 3.7 | 8.4 | 15 | 4 | 0.7 |
| 10 | 11 | 20.4 | 4.7 | 10.5 | 19 | 5 | 0.7 |
| 12 | 13.5 | 23.9 | 5.2 | 13 | 23 | 5.7 | 0.7 |
| (14) | 15.5 | 26.9 | 5.7 | 15 | 26 | 6.2 | 0.7 |
| 16 | 17.5 | 31.9 | 7.2 | 17 | 30 | 7.7 | 1.2 |
| (18) | 20 | 36.4 | 8.2 | 19 | 34 | 8.7 | 1.2 |
| 20 | 22 | 40.4 | 9.2 | 21 | 37 | 9.7 | 1.7 |
Note 1 Size shown in brackets is of second preference.
Note 2 Clearance hole d1 according to medium and fine series of IS: 1821.
Type B for countersink hole size
Countersink holes are suitable for countersink head screws with hexagon sockets. Its various dimensional features are Den in Table II.
Table II
Dimensions and Designation of Countersink-Type B According to IS: 3406 (Part 1) 1986
| For Nominal Size | Fine Series (f) d1 H12 | Fine Series (f) d2 H12 | Fine Series (f) t13 | Fine Series (f) t2+ 0.10 |
| 3 | 3.2 | 6.3 | 1.4 | 0.2 |
| 4 | 4.3 | 8.3 | 1.7 | – |
| 5 | 5.3 | 104 | 2.4 | 0.3 |
| 6 | 6.4 | 12.4 | 2.9 | – |
| 8 | 8.4 | 16.5 | 3.3 | 0.4 |
| 10 | 10.5 | 20.5 | 4.4 | – |
| 12 | 13 | 25 | 5.5 | – |
| (14) | 15 | 28 | 6.5 | – |
| 16 | 17 | 31 | 7 | 0.5 |
| (18) | 29 | 34 | 7.5 | – |
| 20 | 22 | 37 | 8 | – |
| 22 24 | 23 | 48.2 | 8.5 | 1 |
Note 1 Sizes shown in brackets are of second preference.
Note 2 Clearance hole d1 according to medium and fine series of IS: 1821-1982.
Type C for countersink hole size
Countersink holes are suitable for slotted raised countersink (oval) head-tapping screws and for slotted counter (flat) head-tapping screws. Its various dimensional features are given in Table III. It is represented as countering IS: 3406 for countersink type C for screw sizes.
Table III
Dimensions and designation of countersink-Type C according to IS: 3406 (Part 1) 1986
| For Screw Size | d1 H12 | d1 H12 | t13 |
| (0) | 1.6 | 3.1 | 0.9 |
| (1) | 2 | 3.8 | 1.1 |
| 2 | 2.4 | 4.6 | 1.3 |
| (3) | 2.8 | 5.2 | 1.5 |
| 4 | 3.1 | 5.9 | 1.7 |
| (5) | 3.5 | 6.6 | 1.9 |
| 6 | 3.7 | 7.2 | 2.1 |
| (7) | 4.2 | 8.1 | 2.3 |
| 8 | 4.5 | 8.7 | 2.6 |
| 10 | 5.1 | 10.1 | 3 |
| (12) | 5.8 | 11.4 | 3.4 |
| 14 | 6.7 | 13.2 | 3.9 |
| 16 | 8.4 | 16.6 | 4.9 |
Note Sizes given in brackets are of second preference.
Type E for countersink hole size
Countersinks are used for slotted countersink bolts used for steel structures. The dimensions of its van features are shown in Table IV. It is represented as countersink E 10-15: 3406 for a countersink type E of nom size 10.
Table IV
Dimensions and Designation of Countersink-Type E According to IS: 3406 (Part 1) 1986
| For Nominal Size | d1 H12 | d2 H12 | t13 | 1° |
| 10 | 10.5 | 19 | 5.5 | 75° |
| 12 | 13 | 24 | 7 | – |
| 16 | 17 | 31 | 9 | – |
| 20 | 21 | 34 | 11.5 | – |
| 22 | 23 | 37 | 12 | 60° |
| 24 | 25 | 40 | 13 | – |
Note Clearance has d1 according to five series of IS: 1821-1982
Counterboring
Counterboring is an operation of enlarging an existing hole with a flat bottom. The tool used for counterboring is called a counterbore. At the cutting end, a pilot is provided to guide the tool concentric to the previously drilled hole. The pilot also helps to avoid chattering while counterboring.
Spot Facing
Spor facing is a machining operation for producing a flat seat for a bolt head, nut, or washer at the opening of a drilled hole. The tool used is called spot facing tool or spot facer. Spot facing is similar to counterboring, except that it is shallower. Tools that are used for counterboring can be used for spot-facing as well.