Reaming a drilled hole is another operation that can be performed on a drilling machine. It is difficult, if not impossible, to drill a hole to an exact standard diameter. When great accuracy is required, the holes are first drilled slightly undersized and then reamed to size. Reaming can be done on a drilling machine by using a hand reamer or using a machine reamer. When you must drill and ream a hole, it is best if the setup is not changed. For example, drill the hole (slightly undersized) and then ream the hole before moving to another hole. This method will ensure that the reamer is accurately aligned over the hole. If a previously drilled hole must be reamed, it must be accurately realigned under the machine spindle. Most hand and machine reamers have a slight chamfer at the tip to aid in alignment and starting.
REAMERS are precision cutting tools used to enlarge existing holes smoothly and accurately by removing a small amount of metal. Reamer geometry varies widely, having four or more flutes, spiral or straight, and left or right hand cut.
Applications REAMERS are used to rough or finish ream predrilled, punched, or diecast cavities for improved size, roundness, straightness, and surface finish. Though straight flute reamers are still popular, there are many advantages to spiral flute construction. Particularly in smaller sizes, spiral flute reamers can be manufactured more accurately and result in a considerable cost savings.
Limitations REAMER limitations depend upon tolerances and finish desired, amount and distibution of stock, and type of material being cut. Feeds and speeds are critical.
Reamers are made of either carbon tool steel or high speed steel. The cutting blades of a high speed steel reamer lose their original keenness sooner than those of a carbon steel reamer; however, after the first super keenness is gone, they are still serviceable. The high speed reamer usually lasts much longer than the carbon steel type.
Reamer blades are hardened to the point of being brittle and must be handled carefully to avoid chipping them. When reaming a hole, rotate the reamer in the cutting direction only. Turn the reamer steadily and evenly to prevent chattering, or marking and scoring of the hole walls.
Reamers are available in any standard size. The straight fluted reamer is less expensive than the spiral fluted reamer, but the spiral type has less tendency to chatter. Both types are tapered for a short distance back of the end to aid in starting. Bottoming reamers have no taper and are used to complete the reaming of blind holes.
For general use, an expansion reamer is the most practical. This type is furnished in standard sizes from 1/4 inch to 1 inch, increasing in diameter by 1/32 inch increments.
Taper reamers, both hand and machine operated, are used to smooth and true tapered holes and recesses.
DIFFERENT REAMER AND THEIR APPLICATION:
The STEP REAMER is a conventional reamer which has had a second diameter created by grinding down a portion of the larger diameter. They are used to enlarge existing holes, smoothly ad accurately, by removing a small amount of metal. Two diameters allow multiple operations in one productin step. (More than two diameters are possible.) Step reamer geometry is as variable as conventinal reamer geometry.
STEP REAMERS are used to rough or finish ream predrilled, punched, or diecast cavities for improved size, roundness, straightness, and surfacce finish. Multiple diameter construction permits a small amount of metal removal in stages, or other operatins to be performed along with reaming such as creating a chamfer. Because the tool is manufactured with a high degree of concentricity it is possible to achieve better matching results as compared to seperate operations.
STEP REAMER limitations depend upon tolerances and finish desired and type of material being cut. It is not practical to have a small diameter less than 75% of the large diameter. This percentage applies when the reamer has more than four flutes and increases below .188 because .100 is the minimum small diameter on reamers.
STEP DRILL REAMER ( 2-4, 2-6, 2-8 )
A STEP DRILL REAMER(2-4,2-6,2-8) is a two flute drill and a spiral fluted reamer combined into one tool. Step construction limits resharpening life in comparison with a Subland Drill Reamer, but the additional set of reamer lands and ship capacity increases the tools ability to achieve a slightly better tolerance grade. Like the Subland Drill Reamer, this tool construction style is used to span the part tolerance gap achievable with a drilling operation and one requiring a seperate reaming operation.
The STEP DRILL REAMER accomplishes both drilling and reaming in one operation. Results desired should be within the limitations outlined below. Because of its shorter life span, Step Drill Reamers should not be used where Subland construction will achieve the results desired. The use of guide bushings is recommended for all applications.
The STEP DRILL REAMER is not recommended for part tolerances closer than .002" and part thickness shoulkd not exceed 1½ times the reamer diameter. The cavity should be a through hole and the drill should break through before the reamer begins to cut. It is not practical to have a drill diameter less than 90% of the reamer diameter. The diameter ratio will normally be between 94% and 97%. Small diameter minimum is .100.
These heavy duty reamers are designed for use in structural steel fabrication bridge work, and ship construction to line up bolt and rivet holes. Can be used in portable electric or pneumatic equipment. Because of the heavy duty work involved, some sizes have larger Morse Taper shanks than is usual for the diameter.
Taper Pin Reamers are manufactured with a taper with 1/4" per foot. They are used to ream holes into which standard taper pins will fit. The point of each reamer will enter hole reamed by next smaller size. Hole to be reamed should be a few thousandths smaller than the small diameter of the finished reamed hole. Square shank allows hand (straight & spiral) reamers to be held in a tap wrench or vise, depending on whether the reamer or the part is rotated.
Shell Reamers are designed to be used as a chucking reamer for reaming bearings and other similar work. They are fluted almost their whole length and have a tapered 1/8" per foot hole to be used with shell reamer arbors. One arbor fits several sizes of reamers so only 9 sizes of arbors are needed to fit all sizes of reamers.
Taper Shank Car Reamers are designed with a short flute and overall length to permit use in cramped quarters or where a Bridge Reamer would be too long. They are primarily used to repair railroad cars and for construction work, especially involving the rectification of misaligned holes.
Adjustable Hand Reamers are designed with enough adjustment to ream almost any odd size hole encountered in reaming. The blades are made of high speed steel for long life and can be adjusted by loosening one nut while tightening the other. They are used mostly for repair work in the field.
Hand Expansion Reamers are designed to enlarge reamed holes by a few thousandths. The pilot and guide on these reamers are ground slightly undersize for clearance and to guide reamer. The flutes also have a ground starting taper to help guide reamer into hole. Reamer can be expanded slightly by turning adjusting screw on and off reamer.