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Rotary Broach Holders

applications |    uses

 

Applications

ROTARY/PUNCH BROACHES can be used in a variety of machines to cut polygons in
blind holes: Any type of CNC or manual turning, milling, drilling or screw machine.
The practical forming length of rotary/punch broaching is usually up to 1-1/2 times
the size of the broach (measured across flats).

ROTARY BROACH HOLDERS: For optimal tool life in large production settings these
broaches are used in Rotary Broach Holders. Holders and broaches are sold separately
and available from stock for immediate delivery. These holders are for use on any type
CNC or manual turning, milling, drilling or screw machine. The holder has an internal
live spindle, which holds the end cutting broach tool. The centerline of the cutting tool
is offset at 1° from the centerline of the work piece. This causes the broach to wobble
creating a shearing effect as the broach is advanced into the work piece or vise versa
as described below:

BROACHING A ROTATING WORK PIECE: In a turning or screw machine, the holder is
mounted stationary while its internal live spindle and the broach rotates after contact
with the rotating work piece (Diagram A). At the appropriate feed, the work piece is
“sheared” by the pressure of the broach through a wobbling type action producing
the polygon shape desired.

BROACHING A STATIONARY WORK PIECE: In a milling or drilling machine, the holder is
mounted into and rotates with the machine spindle while its internal live spindle along
with the broach remains stationary upon contact with the stationary work piece
(Diagram B). While the machine spindle is rotating, the broach’s pressure shears the
polygon shape into the work piece (wobbling type action).

PUNCHING VERSUS ROTARY BROACHING: Many applications can be achieved without
the rotary broach holder. For the purpose of merely punching a polygon into an
existing pilot hole, these broaches have successfully been used with universal
machining methods.

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Use Recommendations

 

PART PREPARATION: The diameter of the pre-drilled hole should be 1-2% larger
than the measurement across the flats on the broach. Drill the hole as deep
as possible for chip clearance. Countersink with a 90° lead chamfer slightly
larger than the largest dimension of the broach face (distance across points).

CENTERING THE BROACH: The most critical component in running these tools is
having the broach centered as close as possible to the centerline of the work
piece. Improper centering will cause uneven hole configurations, oversize
holes, spiraling, and excessive cutter/holder wear. It is necessary to align the
end of the broach tool to the centerline of the work piece diameter by
means of adjusting the screws located on the sides of the holder. Alignment
instructions are included with purchase of the tool holder.

SPEEDS & FEEDS: Rotational speed (RPM) has very little effect on cutting
speed and tool life. We recommend starting at 1200 RPM with a feed rate
of .016 times the size of the broach in inches for a feed rate in IPR units.
For example the feed rate for a 1/4” rotary/punch broach would be
.016 x .250 = .004”/rev.

COOLANT: The amount of heat generated is minimal. Normal coolant or cutting
oil should be applied on the tip of the broaching tool prior to contacting the
work piece and not inside of the work piece pilot hole. Trapped fluid may
not be able to escape, causing inability to broach to full depth.

BROACH TOOL MATERIAL: Broaches are customarily manufactured from M-2
high-speed steel. This material provides the required edge toughness for
standard operations, which do not generate enough heat to effect tool life
in machining most metals. However, for broaching materials such as ductile
iron, tool steel, stainless steels, titanium alloys, or nickel-cobalt alloys, a
cobalt or PM-4 powdered metal broach would be recommended for optimal
tool life. Coatings are also available.