easy way – A term of art in tube-bending for the orientation of a non-round tube shape relative to the plane of bend; in an “easy way” bend the major axis of the tube shape is perpendicular to the plane of bend.  Occasionally called an “E-way” bend.  Compare hard way.

eccentricity – The deviation of the center point of tube’s inside diameter from the center point of its outside diameter; normally in tube milling the permissible level of eccentricity is specified by a wall thickness tolerance.

elastic limit – The limit beyond which a material under a stress loses its elasticity and permanently deforms.  The elastic limit is a useful concept in understanding how to maximize the life of a wiper die.  See wiper for details.

elasticity – The capacity of a material to return to its original shape after the stress it was under is released.

electric resistance welded steel tube, ERW steel tube – A common tubing material.  See steel.   

elongation – The thinning and stretching of the extrados of the tube while under the force of the bend forming process.  If the elongating force exceeds the elastic limit of the tubing material, the tube will split or tear.  Normally the elongation of tube is specified as a percentage of its original length.  Compare compression, Definition #1.

empty bending – A trade name for bending with heart-shaped cavity tooling.  See cavity.

EMT - See IPS.

end link – The component which joins the end ball to the rest of the mandrel assembly.  The end link is distinguished from the center link by having a solid base instead of a socket.  See link.

end tangent – The tangents at the leading and trailing ends of a bent tube.  The length of the end tangents plays a role in specifying clamps and final positioning of the collet.  Sometimes this term is restricted to meaning only the trailing end tangent.  Compare mid-tangent; also see tangent.  See geometry for illustration.

extrados – An architectural term borrowed by tube-bending to describe the geometry of material flow.  The extrados is that section of the tube which is undergoing elongation during the bend forming process; that part of the tube of which the wall thins.  Roughly, the extrados corresponds to outboard half of the tube bend, but in fact includes a significant portion of the tangents and some of the tube inboard of the centerline radius.  The extrados is separated from the intrados by the neutral axis.  Compare intrados; see neutral axis and point of bend.  See geometry for illustration.

feathered edge – The sharp semi-circular edge of a wiper die determined by the intersection of the radius face with the cavity.  Because this intersection occurs at the line of tangency (see the entry under aero-cut for an alternative design), theoretically the thickness of the feathered edge should be zero, but this is not practicable for either the manufacture of the wiper or its end use.  In actuality, the origin point of the radius face is offset slightly from the centerline of the tube cavity to give the feathered edge a slight thickness.  This is known as simple-sweep geometry.  The formula for determining the optimum thickness is F = t x .004 where “F” is thickness of the feathered edge and “t” is the tube diameter.  See wiper.

flash – See seam.

flattening – The reduction in the diameter of the tube as the lengthening outside radius pulls inwards while being stretched between the clamp die and pressure die.  Reduction is mitigated by reducing drag at the point of bend.

[CLICK HERE FOR INSTRUCTIONS ON REDUCING FLATTENING WITH THE 4-STEP SET-UP PROCEDURE]

flexure – 1. Bending about a joint, such as a mandrel ball and link.

2. Loosely, torsion.

follower die – A type of pressure die which moves forward and “follows” the rotation of the bend die during the rotary-draw bending process.  Most modern machines are equipped with the follower type of pressure die as opposed to the static type.  Compare static die; see pressure die.

forward mandrel set-up – The preferred method of setting up a rotary-draw tube-bending machine in which the mandrel nose is used to fullest effect to control the flow of material at the point of bend.  Sometimes this is called the “forward-mandrel, low-pressure” set-up because forward placement of the mandrel permits the machine operator to lower the direct pressure, thus reducing drag at the point of bend.

[CLICK HERE FOR INSTRUCTIONS ON THE 4-STEP SET-UP PROCEDURE]

forward tangent – The straight section ahead of bend being formed.  Compare back tangent; also see tangent.  See geometry for illustration.

gauge, gage – See Birmingham Wire Gauge.

geometry – The idealized geometrical elements of a tube bend as opposed to the physical regions of the tube bend.  Related geometrical and physical terms are often used synonymously, but should be distinguished because each define fundamentally important but different aspects of the tube bend.  For example:

Line of tangency (geometry) vs. point of bend (region)

Centerline radius (geometry) vs. neutral axis (region)

Inside radius (geometry) vs. intrados (region)

Outside radius (geometry) vs. extrados (region)

grip – 1. The ability of a clamp to hold a tube as it is drawn around the bend die.  See clamp die.

2. A clamp or clamp die.

half-round – A common style of wiper die in which the body is semi-circular as opposed to rectangular; the standard style for inserted wiper dies.  Compare square-back; see wiper.

hanger bracket – A small plate or tab fastened to the pressure die (and for some machine models, the clamp die) in order to fixture the die to the machine by means of hanging it from the follower bar (or clamp slide block).

hard chrome – The most common plating used on steel bending tools to extend tool life and prevent galling.  Usually only mandrel balls and noses are hard-chrome plated.  Occasionally the bore of a wiper or the cavity of a bend die is hard-chromed.  However, the feathered edge of a plated wiper can become excessively brittle, therefore it will often fail before wearing out.  The plating of a bend die cavity does not pose any significant drawbacks, but it is seldom cost-effective to do so.

Hard-chrome plating is recommended for steel tooling to bend non-ferrous materials, aluminum and copper in particular.  It should not be used for black pipe, high-carbon steel, chrome-moly steel, stainless steel, titanium, and Inconel tubing; aluminum-bronze is recommended instead.  Hard-chromed tools are effective for bending mild steel and aluminized tubing if the machine has a good lubrication system to flush away debris that might otherwise build up at incipient cracks in the plating.

hard way – A term of art in tube-bending for the orientation of a non-round tube shape relative to the plane of bend; in a “hard way” bend the major axis of the tube shape lies in the plane of bend.  Occasionally called an “H-way” bend.  Compare easy way.

head – That part of center or end link which contains the detent system and is inserted into the socket another link to form a flexible joint.  See link.

heart-shaped cavity – A cavity design used to bend tubing without the benefit of a mandrel and wiper.  See cavity.

holder – The wiper holder.  See wiper.

hot bending – A method of bending in which the ductility of the tubing material is increased by heating it either before placement on the machine or in-process.  Usually in-process heating of the material is done indirectly; heating elements are fixtured in the tools and so the material is heated by conduction through the tools.  Few bending applications benefit from hot bending; even titanium is bent cold today more often than hot.  Compare cold drawing.

hot rolled steel tube – A common tubing material, especially for pipe and non-round shapes.  See steel.

H-type link – The most common style of mandrel linkage, originally developed in the late 1950’s to reduce pitch and permit universal flexure of the mandrel balls.  A significant improvement over brute links, which see.  H-type links come in two major varieties, poppet and split.  The original H-type link was of the split variety because of limitations in machining and metallurgical technologies at the time of its development.  The poppet style has the advantages of being a single piece and therefore can carry a heavier load and less expensive to produce.  Compare brute link.

hydroforming – A metalforming process which is displacing stamping in a wide range of applications, especially in the automotive industry.  Hydroforming is important to tube-bending, because many parts to be hydroformed start off as tubing which is bent into the approximate shape of the finished part before going into the hydroforming press.  Hydroformers call this bending operation “pre-bending”, which see.  Pre-bending is rotary-draw tube-bending and does not differ in the fundamentals from any other rotary-draw tube-bending process.

ID – Abbreviation for inside diameter, which see.

induction bending – An old method of bending very large diameter pipes without dies by heating a narrow section of the pipe and then putting as deep a bend as possible in it without causing the material to buckle or split.

industrial grade tooling – An obsolete marketing term.  See commercial grade tooling.

insert link – The link which attaches the ball sub-assembly to the mandrel shank.  Functionally the insert link is the same as a “mandrel link” or “shank link” but applies specifically to inserted mandrel assemblies.  See link.

inserted bend die – The most common type of bend die consisting of a radius block and a detachable clamp insert section.  See bend die.

inserted mandrel assembly – A mandrel assembly in which the shank consists of a steel body and a replaceable nose insert.  See mandrel.

inserted wiper die – A wiper die in which consists of a steel wiper holder and a replaceable tip insert.  See wiper.

inside diameter – The bore of a tube or pipe; the outside diameter of a tube or pipe less twice the wall thickness.

inside radius – A specification for the arc of a tube bend, most commonly used with non-round tubing.  (The centerline radius, which see, is almost always used to specify the bend of a round tube.)  Physically, it is the innermost edge of bend; geometrically, it is the continuation of the inboard line of the tube into the arc.  Compare intrados.  See "ISR" under geometry for illustration.

interlock (bend die) – A common feature of bend dies; a pair of tabs extending circumferentially from the top and bottom surface of the die which interlock with mating shoulders on the clamp and pressure dies.  The purpose of interlock is to help hold the clamp and pressure dies in the plane of bend, especially on older machines.  Occasionally the bend die will have the shoulders and the clamp and pressure dies the tabs; this is called “reverse interlock”.  See bend die.

interlock (wiper) – A common feature of inserted wiper tooling; the tip insert is keyed to the wiper holder, usually by means of a circumferential groove interlocking with a mating ridge in the pocket of the holder.  The purpose of this interlock is to help the insert resist being dragged from its seat in the pocket of the holder while under direct pressure.  See wiper.

intrados – An architectural term borrowed by tube-bending to describe a region of material flow.  The intrados is that section of the tube which is undergoing compression during the bend forming process; that part of the tube of which the wall thickens.  Roughly, the intrados corresponds to inboard half of the tube bend, but in fact does not extend all the way to the centerline radius.  The intrados is separated from the extrados by the neutral axis.  Compare extrados; see neutral axis and point of bend.  See geometry for illustration.

IPS – A pipe specification system which associates certain nominal pipe diameters with standardized wall thickness called “schedules”.  The EMT system is identical to the IPS system for all practical purposes.

The same schedule number will have a different fixed decimal inch value for each nominal diameter.  For example the wall thickness for 1” Schedule 40 pipe is .133”, but for 2” Schedule 40 pipe is .154”.  It is also important to note that the nominal diameter in this system vary considerable from the true diameter.  For example, 1” pipe has a true diameter of 1.315” and 2” pipe has a true diameter of 2.375”.  Furthermore, the bend radius of pipes in the IPS system are often expressed in terms of “D” of bend.  If so, the “D” is the multiple of the pipe’s nominal diameter, not its true diameter.  For example, the centerline radius of a 2-“D” bend of a 1” pipe is 2.0” inches, not 2.63” inches.

See our IPS Chart under "Conversion Formulas" for a complete table of the true values of nominal pipe diameters and schedules.