DEFINITION:
Reamers are used to finish machine a previously formed hole to an exact diameter with
a smooth finish. It should not be used to significantly enlarge a hole (max. 5% –
depending on material and hardness).
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 die cast
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 reamers limitations depend upon tolerances and finish desired, amount and
distribution of stock, and type of material being cut. Feeds and speeds are critical.
The reamer is an end cutting tool, cutting only on the chamfer's edge at the outside
diameter of the preformed hole. The standard 45° chamfer angle provides effective
cutting action for most materials.
Standard geometry reamers tend to follow the axis of the existing hole. Misaligned or
crooked holes can be straightened by increasing the chamfer angle - sometimes a 180º
flat end is very effective. This is a simple modification.
REAMER MATERIALS:
Reamers are made of either carbon tool steel, high speed steel, carbide or carbide
tipped. 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.
Carbide tipped reamers are especially appropriate for close tolerance reaming. Because
carbide is very highly resistant to wear, the reamer will produce accurate hole size and
a smooth finish far longer than high speed steel or cobalt.
REAMER TYPES:
General Purpose – Superior performance over high speed steel and cobalt; good in a
wide variety of materials
Material Specific – Excellent in large production runs due to material specific carbide &
tool geometry
Coolant Fed – Exceptional performance and tool life using material specific reamer
technology and coolant fed capabilities; maximizes feeds & speeds.
REAMER GEOMETRY:
Straight Flutes - usual general purpose.
Right Spiral Flutes - tend to bridge interruptions such as key-ways, slots or intersecting
holes. Good chip clearing ability for ductile materials and blind holes.
Left Spiral Flutes - also tends to bridge interruptions. Good for hard cast iron, heat
treated steels and other hard materials. Do not use in blind holes.
Length of carbide - usually partial but full length carbide should be selected for deep
holes and abrasive materials.
Coolant feeding types have advantages - up to twice conventional feed rates and will
hold size much longer. improved hole surface finish. excellent chip disposal. Lubricates
and cools the cutting edge. Center Feed for blind holes. Flute Feed for through holes.
Expansion reamers - Economical for abrasive materials.
TOLERANCES AND FEATURES:
Tool diameter tolerance:
General purpose & Coolant fed
Thru 11/2" tool diameter: plus .0003", minus .0000"
Over 11/2" tool diameter: plus .0004", minus .0000"
Material specific (NAS)
Thru 1/2" tool diameter: plus .0002", minus .0000"
Over 1/2" tool diameter thru 3/4": plus .0003", minus .0000"
Over 3/4" tool diameter: plus .0004", minus .0000
Shank diameter tolerance:
General purpose
minus .0005", minus .0015"
Material specific (NAS) & Coolant fed
Thru 23/32" tool diameter: plus .0000", minus .0010"
Over 23/32" tool diameter: plus .0000", minus .0015"
Modified tool diameter
Non-stocked metric tool diameter
Closer tool diameter tolerance
Cutting diameter reduced for step or pilot
End chamfer other than 45°
End cutting or corner radius
Increased/decreased circular margin
Increased/decreased tool diameter back taper
Shortened shank
Reduced shank diameter
Flat(s) on shank
Tanged shank
Shank whistle notch for set screw
Smaller taper shank
Coatings available to increase tool life
REAMER STYLES:
Hand Reamers
Solid hand reamers should be used when a greater accuracy in hole size is required.
The cutting action of a hand reamer is performed on the taper (approximately 0.015 per
inch) which extends 3/8-to 1/2-inch above the chamfer. This slight taper limits the stock
allowance, or metal to be removed by the reamer, from 0.001- to 0.003-inch depending
on the size of the reamer. The chamfer aids in aligning and starting the tool, and
reamers usually have straight shanks and a square end to fit into an adjustable tap and
reamer wrench. A hand reamer should never be chucked into a machine spindle for
power reaming. A center may be installed in the drilling machine spindle to align and
center the hand reamer. As the reamer is turned by hand into the hole, only a slight
pressure is applied to the hand feed lever to keep the center in contact with the reamer
and maintain accuracy in alignment.
Machine Reamer
Machine reamers can generally be expected to produce good clean holes if used
properly. The cutting action of a machine reamer is performed on the chamfer and it will
remove small amounts of material. The allowance for machine reamers is generally
1/64 inch for reamers l/2-inch to 1 inch in diameter, a lesser amount for smaller holes,
and greater than 1/64-inch for holes over 1 inch. Machine reamers for use on drilling
machines or lathes have taper shanks to fit the machine spindle or straight shanks for
inserting into a drill chuck. A reamer must run straight and true to produce a smooth
finish. The proper cutting fluid for the metal being cut should be used. Generally, the
speed used for machine reaming would be approximately one-half that used for the
same size drill.
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.
Expansion Reamer
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 Reamer
Taper reamers, both hand and machine operated, are used to smooth and true tapered
holes and recesses.
DIFFERENT REAMERS AND THEIR APPLICATION/LIMITATIONS:
Step reamers
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 production step. (More than two diameters are possible.)
Step reamer geometry is as variable as conventional reamer geometry.
Applications
Step reamers are used to rough or finish ream predrilled, punched, or die cast cavities
for improved size, roundness, straightness, and surface finish. Multiple diameter
construction permits a small amount of metal removal in stages, or other operations 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 separate operations.
Limitations
Step reamers 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
tool’s 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 separate reaming operation.
Applications
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.
Limitations
The step drill reamer is not recommended for part tolerances closer than .002" and part
thickness should 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.
Chucking reamers – carbide tipped
Carbide tipped chucking reamers are used for reaming highly abrasive materials and
sizing holes that have work-hardened. They are also used when sand or scale is
encountered in reaming holes in castings. Tolerance is +.0003" - .0000".
Taper shank bridge reamers
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
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
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
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
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
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.
Single Point reaming with Guide Pads
Machining cam bores in automotive cylinder heads is not for the faint of heart. The tight
tolerances on diameter, roundness and straightness, the requirement for visually
perfect, minor-like surfaces, and the long length and relatively small diameter of the
interrupted bore are all factors that make cam boring an extremely demanding
operation.
The design of these boring tools and the precision with which they are manufactured
are the critical elements for their successful application.
Pads are independent of the blade guide and support the tool in the bore. This balances
cutting forces with the pad-support reaction force for enhanced tool performance.
Single-blade, pad-guided tools share numerous special features:
They are long in relation to their diameter and are typically made from heavy metal for
greater strength and rigidity.
The multiple guide pads have extended lengths for enhanced stability and alignment.
Tools that feature a single, replaceable blade, usually made of carbide and sometimes
tipped with PCD, provide enhanced performance when boring aluminum cylinder heads.
The blade is rigidly supported in the bore by multiple guide pads. This design allows the
tool to achieve an accurate bore size with a fine surface finish and superior hole
geometry.
Because conventional multi-fluted reamers are guided by their cutting edges, they
generate a slightly irregular hole geometry when finishing cam bores. The single-blade,
pad-guided design separates the cutting and guiding functions of the tool so that each
function can be optimized. Because the cutting blade is independent of the tool body, it
can be micro-adjusted over a limited range and preset to a specific cut diameter, which
the tool achieves
Special internal coolant porting provides adequate coolant flow to the cutting edge and
guide pads.
An optional PCD-tipped blade achieves long tool life in cutting cylinder heads made of
cast aluminum.
There are several ways to approach a
cam-boring operation. Cam-boring tools can be run on a transfer line or on a machining
center. When running on a transfer line, the tools are installed in a specialized
machining station.
Cam boring is usually accomplished with the use of a special spindle unit, commonly
known as a “squirt-out” spindle. It incorporates an outboard rotating bushing, which
provides critical support and alignment as the tool enters the first journal. As successive
journals are machined, the guide pads offer support in the previously machined journals
and in the bushing.
One automotive manufacturer applies semi-finishing and finishing single-blade, padguided tools to machine cam bores. Running on a transfer line, the cutting tools achieve
a consistently accurate size of 27.0mm, within the close tolerance range of ±12.5pw
(±0.0005). And the surface finish of ~ to 10 Ra is much better than the required finish of
30 Ra.
The PCD-tipped tools are applied at a feed rate of 0.005 ipr and a spindle speed of
4,000 rpm to machine the camshaft bores in the aluminum cylinder heads. The
concentration of the semi-synthetic coolant is 10 percent The PCI) blade produces
100,000 parts before needing to be replaced.
In some transfer line applications, the rotating bushing is not used. A short tool is used
to machine the first journal. It then serves as the bushing for the longer tool to machine
successive journals.
This was the scenario for another automotive manufacturer that was also machining
camshaft bores in aluminum cylinder heads. Its tools were also run at a 0.005-ipr feed
and a spindle speed of 4,000 rpm. The concentration of semi-synthetic coolant was 10
percent. A 10 Ra finish was imparted to the 0.6299’ bore. Tolerance was ±0.0007’.
Running cam-boring tools on machining centers is becoming more common. A two-tool
combination, similar to the tool design described in the second application, is used. A
short tool machines the first journal, producing a qualified pilot hole for the longer tool
that follows. Guide pads provide support for the longer tool as each successive journal
is machined, with each machined journal functioning as a bushing while the next journal
is machined. In many of these applications, semi-finishing and finishing are
accomplished with the same tool, which machines both cuts sequentially in a single
pass. When it comes to tackling the demands of machining cam bores in automotive
cylinder heads, tools with a single, replaceable blade supported by guide pads offer an
effective solution.
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.