MODEL 3 TUBE BENDER
Assembly & Operating Instructions
Online Ordering Available Through Medford Tools and Supply Inc
1-800-841-1133

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Die Set Components

 

A Die Set refers to the components that are used in the bender to hold the tubing or pipe during the bending operation. This
section does not describe the operation of the bender. This section's purpose is to simply familiarize you with the different
components that make up a 'Die Set'. Knowing how the different die set parts interact with each other is essential in operating
the bender correctly. The die set must match the size of the tubing or pipe being bent. For example, never bend 1 1/2" tubing in
a 1 5/8" die set. This may damage the followbar's inserts.
First, let's explain the difference between tubing and pipe. Tubing is specified by its outside diameter and a wall thickness.
For example, 1 1/2" x .095" tubing has an outside diameter of 1 1/2" and a wall thickness of .095". On the other hand, pipe is
specified loosely on its inside diameter. We say loosely because the pipe's size may not actually be its inside diameter. Confused
yet? Just remember pipe is commonly used for the purpose of transporting fluids. Fluid flow is only concerned with the inside
area of the pipe and the outside makes no difference what so ever. Pipe wall thickness is specified as a schedule number and
is obtained from a pipe chart. Another example, 1 1/2" schedule 40 pipe has an outside diameter of 1.900" (larger than 1 7/8")
and a wall thickness of .145" and an inside diameter of 1.610" (near 1 5/8"). So, when ordering die sets be careful to specify whether
it's a tube or pipe size die set.

 

ROUND GROOVE DIES:
A Round groove die set consists of three main elements:

 

1) Forming Die
This is the part that the tube or pipe actually bends around. It has a circular groove machined around its circumference.
Please note that this groove is machined with a specially designed profile to help in reducing flattening of the bend's outside.
If you lay a section of tubing into the forming die you will notice that it will NOT completely seat into the die's groove. This is
normal for tube size dies and becomes very important as the tube's wall thickness gets thinner. However, forming dies that
are machined for 'Pipe' instead of tubing are generally not manufactured with this profile and the pipe may completely seat
in the groove. Pipe is much more forgiving when it comes to bending it because of its thicker wall. Stamped into the top is

the Outside diameter of the tube or pipe and the centerline radius (CLR) of the forming die. Above is pictured a 3/4" die with
a 2 1/4" CLR and a 1 1/2" die with a 4 1/2" CLR.
Drive holes are drilled into most dies with a radius of 3" or larger. When the 7/8" drive pin is inserted into the drive links,
it will pass through these holes. This is how the drive links rotate the forming die. The 1" drive holes are drilled oversize to
permit easy insertion of the 7/8" drive pin.
Die sets with a radius smaller than 3" will generally not have drive holes because there is no room to drill them. As
explained in the following section on how to operate the bender, the diameter of the tubing or pipe is so small the bender
can be operated without the use of the ratchet mechanism.

 

2) U-Strap
U-straps are sized to the OD of the pipe or tubing being bent. The
size is stamped onto them.
 
 
3) Followbar (Also referred to as the Pressure Die)
The Followbar is the component that presses the tubing into the forming die to create the bend. Shown in the illustration below, it consists of three main parts: a backing block, an angled rear insert and a straight 0 degree front insert. This multipart design allows the inserts, if damaged or worn out, to be inexpensively replaced without having to purchase a whole followbar assembly. The Inserts are permanent cast from a special bearing grade anti-galling material to protect the tubing from scratching during the bending process and then CNC machined to size. They are silverish in color but are NOT aluminum.

 

REPLACING INSERTS
The placement of the inserts into the backing block
must be done properly or poor quality bends will result.
Notice one insert is marked 0 degrees. The other insert
will be marked with the angle that is appropriate for the
radius of the forming die (usually 3 or 5 degrees). The
angle in the rear insert helps to support the tube or pipe
after the point of bend, greatly reducing flattening. When
bending, the angled insert will always be closer to the
forming die, and the U-strap for that matter, than the 0
degree insert. Notice in the figure to the right, that the tall
side of the angled insert must face the U-strap side of the
die.
The front 0 degree insert has a chamfer machined
into one side of its groove. This chamfer must face away
from the rear insert, thus allowing the tube or pipe to slide
through easier.
To replace the inserts, simply lay the Backing Block
flat with the engraving facing up. The Backing Block may
or may not be as thick as the inserts. If it is thinner, place
spacers under the Backing Block so that when the inserts are inserted they are centered in the dovetails. This is important.
Now tighten the 1/2" locking bolts and you're done.

COMPLETE ROUND GROOVE DIE SET
Above is pictured all of the components which make up a complete die set for round tubing or pipe. In the figure to right,
you can see two red lines drawn at 90 degrees apart. These lines are marked as 1 and 2. Line 1 runs from the center of
the forming die's center hole to approximately the middle of the angled rear insert. Line 2 runs from that point parallel to the
tubing. This illustrates the basic principle of how the components relate to each other. It is vital that when bending the rear
insert is positioned as shown. For example, suppose the followbar in engraved with hole 6 as shown, but you install it in
hole 7. The rear insert will be shifted to the right of line 1 and the angle machined into it will have no effect during bending.
This will generally cause flattening of the tubing's outer side and may also cause wrinkling. If you experience this problem
and you have the followbar installed in the correct hole, the rear insert's bending position can be easily checked. Simply place
a short piece of tubing into the bender as if your were actually going to bent it. Apply enough bending force to remove any
play but not actually bend the tubing. Now hold a 90 degree carpenter's square above the bender so that its outside edges
are positioned similar to the red lines shown. The center of the angled rear insert should be roughly at the corner of the square.
I say roughly because some dies are designed to shift the insert slightly to the left or right of center to improve bend quality.
However, this will generally be less than 1/4". If as in the example above, you placed the followbar in the wrong hole, the
insert will be very noticably off center and almost always to the right of red line 1.
 
 
SQUARE AND RECTANGULAR GROOVE DIES:
Square groove dies operate similar to the round groove dies explained earlier with these exceptions:
1) The bottom of the groove has a raised crown machined into it. This starts the depression in the bottom
side of the tubing during bending to prevent the tube from kinking and helps keep the sides reasonably
straight. Note that square tubing will always sink in on the outside and inside of the bend.
2) The U-strap clamp uses a bolt to tightly secure the tubing to the die block. This bolt presses against
a H shaped steel plate to prevent the
bolt from marring the tubing. To the
right is an illustration of the tubing
installed in the forming die.
3) The followbar does not utilize inserts.
It is machined from one solid piece.
4) You must lubricate both the outside
of the tubing and the COMPLETE
groove in the forming die before
bending. Square tubing tends to
wedge itself into the forming die while
bending and generally requires a
large rubber mallet to tap it out when
finished. The bigger the tubing, the
worse the problem. Without lubricant
it can be very difficult to remove the
tubing from the die. This problem is
not specific to the Model 3 Bender,
but to ALL benders utilizing a one
piece die.

 

 

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