In this article we will discuss about the meaning and types of reamers.
Meaning of Reamers:
Reamer is a rotary cutting tool (of cylindrical or conical shape), used for enlarging or finishing to accurate dimensions a hole previously formed. It is usually equipped with two or more peripheral grooves or flutes which may be parallel to axis (straight reamers) or in a right or left-hand helix (fluted or spiral reamers). Latter type produces better finish due to smooth shear cutting. The flutes on reamer body act both as cutting teeth and as grooves for accommodating the chips removed.
The size of the reamer is specified by the diameter measured across two margins, at the cutting edge, on a diametric line. These may be made from high carbon steel, HSS, cast alloys cutting material, and cemented carbide forms. These are made in many different forms (Refer Fig. 18.35). These may be solid or inserted blade type, adjustable or non-adjustable type, be designed for manual operation (hand reamers) or for machine use (Chucking reamers).
Types of Reamers:
1. Hand Reamers:
ADVERTISEMENTS:
They are fluted reamers having a slight taper on the cutting end to facilitate entering a hole properly. These may be solid or expandable type (with limited expansion). The blades are usually spaced irregularly around the reamer body. This is done to reduce the tendency to chatter that a reamer has because of slippage or torsional deflection.
Machine reamers usually incorporate a chamfer of 45° on the cutting end. These are used in turret lathes and screw machines. These may be classed as fluted or rose type. Fluted reamers cut principally on the chamfer and have radial clearance to very narrow margins of 0.2 to 0.4 mm in width to assure free cutting.
ADVERTISEMENTS:
Rose reamers are heavy bodied fluted reamers, which incorporate back taper or longitudinal relief on diameter with a chamfer of 45° and no radial relief on the periphery. Rose reamers are used for roughing and for reaming thin stock.
Reamers are made in a wide range of sizes and number of flutes (which varies from 4 for nominal diameter of 3 mm to 16 for 50 mm diameter). Number of flutes is usually even. Flutes should be wide and deep enough to accommodate the chips when cutting, lands be large enough to prevent deflection back of the cutting edges and of sufficiently large sections to contain enough metal to dissipate adequately the heat generated at the cutting edges.
Reamers are either hand or machine type. These may be cylindrical or taper, depending on the form of the hole to be made. Reamers have from 6 to 16 flutes, usually with irregular spacing along the circle for better quality of reamed holes.
A straight-shank hand reamer (Fig. 18.37) has a body, a neck and a shank. The body comprises a cutting section (starting taper) with a 90° bevel, a cylindrical section to size the hole, and a back-tapered section. The cutting section, which does the main part of the work in operation, is much longer in hand reamers than in machine reamers, where it is termed the chamfer. The cutting section of the reamer has angle ϕ. For making through holes, the angle is as follows: ϕ = 0.5° to 1.5° for hand reamers, ϕ = 12° to 15° for machine reamers and ϕ = = 30° to 45° for carbide-tipped reamers.
For blind holes, ϕ = 45° for hand reamers, ϕ = 60° for machine reamers, and ϕ = 75° for carbide-tipped reamers.
The cylindrical sizing section of the body serves to guide the tool and to size the hole. The back taper reduces friction against the reamed surface and prevents the cutting of oversize holes. To effect the back taper, the diameter of the sizing section is reduced towards the neck by 0.005 to 0.008 mm for hand reamers, and by 0.04 to 0.08 mm for machine reamers.
The rake angle is γ = 0° for finishing high-speed steel reamers, γ = 5° to 10° for roughing high-speed steel reamers, and γ = 0° to 5° for carbide-tipped reamers. The relief angle is α = 6° to 10° on both the chamfer and the sizing section of the reamer.
2. Jobbers Reamers:
ADVERTISEMENTS:
These are similar to hand reamers, the only difference being that these incorporate taper shanks and a 45° chamfer on the cutting end to permit machine use.
3. Shell Reamers:
These are intended to be mounted on special arbors fitted with driving pins or lugs for use on machines.
4. Chucking Straight Fluted Reamers:
ADVERTISEMENTS:
These are intended for free cutting material and for finish reaming holes to size. These are used in drill presses, lathes, automatic screw machines, etc.
5. Helically Fluted Chucking Reamers:
These have right hand flutes and are intended to accomplish a shear cut to produce smooth, true, and accurate holes in stainless steels and materials having hardness of 200-400 Brinell. In soft materials they have tendency to dig and spoil the work.
6. Stub Screw-Machine Reamers:
These incorporate right hand flutes and a hole in the shank for use in a floating holder.
7. Diemaker’s Reamers:
These are used for diemaking and have three flutes and a high helix angle for rapid cutting.
8. Taper Pin Reamers:
These incorporate taper equivalent of the standard tapers for tapered keys.
9. Structural Reamers:
These incorporate Morse taper shanks and are intended for machine use. These are used in ship and bridge building etc. where steel plates and shapes have holes punched/drilled in them that are undersize and rough and where it is necessary to ream the holes when assembled to obtain alignment and proper size for admitting bolts/rivets.
10. Straight Flute Reamers:
These are used for assembly work for reaming bushing holes to specified fits.
11. Helical (Spiral)—Flute Reamers:
These are suited for use in brass or bronze and for reaming holes containing slots, keyways, oil channels, etc.
12. Expandable Reamers:
These are used to produce holes of varying diameters over a limited range. These lack the rigidity of solid type and are used for removing small amount of material. These use a tapered, screw type expanding pin to move the blades radially and to change the diameter.
13. Carbide Reamers:
The use of carbide reamers results in high resistance to abrasion, thereby giving longer tool life and superior finish. These are operated at 1.5 times the speed used for H.S.S. reamers. Solid carbide reamers generate a true hole around their own axis, instead of following previously drilled hole. Large size reamers are made with carbide tips which are either brazed or held on a steel body.
14. Floating Reamers:
These are used to correct the misalignment between the axis of the reamer and the previously drilled hole. Floating reamers consist of two replaceable and adjustable cutting edges which are held in a slot in the reamer and allowed to float in radial direction (the diameter and amount of float being adjustable). These can be used only with rotating workpiece as on turret lathes.
15. Feeds and Speeds:
Reamers should be operated at slower speeds. (70%) and higher feeds (300-400%) than corresponding size drills. Slow speed affects productivity and high speeds cause the material to cling to the edges and lands of the reamer, resulting in premature dulling of the cutting edges and rough holes. Too fine feeds cause excessive wear due to reamer idling the cut. Too coarse feeds tend to produce spiral marks or wavy finish.
A suitable coolant is desirable in reaming most metals except cast iron (cut dry).