A somewhat different design of tool that can achieve the irregular
hole shape of a broach is called a wobble broach. This type of tool is
often used on rotating machines such as lathes. The wobble broaching process is also called rotary broaching.
The tool has a contour similar to the desired final shape but the
leading edge of the tool is wider than the body. The tool is free to
rotate but the axis of rotation is inclined slightly to the axis of
rotation of the work. A typical value for this misalignment is 1
degree. As the work rotates, the broach is pressed against it and
rotates synchronously with it. However, since the axis of rotation is
different, the leading (cutting) edge of the broach "wobbles" with
respect to the work.
If the tool is inclined at an angle of 1 degree to the work, the sides of the tool must have a 1 degree or greater draft.
Ideally the tool advances at the same rate that it cuts. So a 1/2" diameter tool should advance at 0.009" per revolution.
If it advances any faster than that then the tool becomes choked, if
it advances any more slowly then you get an interrupted or zig-zag cut.
Since all work material is elastic, you would actually cut a little
less than the ideal rate just to release the load on the non-cutting
edge of the tool.
There is some spiraling of the tool as it cuts so the bottom of the
hole may be rotated with respect to the top of the hole. Spiraling may
be undesirable because it binds the body of the tool and prevents it
from wobbling freely. One solution to this is to reverse the rotation
in mid cut causing the tool to spiral in the opposite direction. If
reversing the machine is not practical, then interrupting the cut is
another possible solution.
In general, a wobble broach will not cut as accurately as a push or
pull broach. However, the ability to use a wobble broach on high
production machinery such as a screw machine makes this a desirable manufacturing method.
A broach is a series of progressively taller chisel points mounted on a single piece of steel, typically used to enlarge a circular hole into a larger noncircular shape such as a square or other desired shape.
Another typical use of a broach is to cut splines or a square keyway (see image) on objects such as gears, driveshafts, pulleys
etc. The amount of material removed by each broach tooth (or chisel)
varies with the material being cut. A broach tooth designed to cut
steel might remove only 0.05 mm (0.0025 inch), while a broach tooth designed to cut brass
might remove as much as 0.10 mm (0.004 inch). The succession of teeth
(chisels) removes the total amount of material required. A broach may
also be designed to be pushed or pulled through an existing hole; broaching machines are therefore designed accordingly.
Broach (metalwork) A metalworking tool with a series of chisel points mounted on one piece of steel.
Broach (sailing) A sudden instability in the heading of a sailboat when sailing downwind.
Broach (submarine)
Submarines operating submerged are said to have broached the surface
when a portion of the ship (such as the sail, bow, or screw) other than
a mast or antenna comes out of the water. This is similar in intent, if
not in 3-D direction, to the use of broach to describe instability in
heading of a sailing ship.
BROACH warhead
Brooch (or broach): Decorative item designed to be attached to garments.
Bharuch (also known as Broach): A district in south Gujarat state in India.