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

Page 4

 

Die Set Installation and Bending Procedure
There are two types of forming dies provided for the Model 3 Bender. Those with drive holes and those without. The drive holes
are the five 1" holes drilled in a circular pattern around the forming die's center hole. A 7/8" diameter pin inserts through the drive
links and through the forming die's drive holes when in operation. The drive holes are drilled 1/8" oversize to provide easier pin
installation. To prepare for bending, follow the steps below depending on the type of die set. NOTE: The procedures below
describe using the degree indicator. To install an indicator onto your forming die, please refer to that section earlier in this manual.

 

WITH DRIVE HOLES:
Place the forming die into the bender using the 1"
frame pin. If bending square tubing, thoroughly lubricate
the forming die's groove. However, if bending round
tubing or pipe, NEVER lubricate the forming die's groove.
If you do, the tube will tend to slip backwards in the die
while bending, which in turn causes the tubing to kink or
wrinkle. Place the tube into the forming Die. Install the UStrap
with the shorter 7/8" U-strap pin. If necessary,
tighten the U-strap bolt to prevent the tube from slipping
through the die will bending. It's a good idea to cut a slice
out of a bigger piece of tubing place it between the bolt and
tubing to prevent the bolt from dimpling the tubing. If
bending thin wall tubing (.065" or thinner) you must
always use the U-strap bolt.
Next, using the 7/8" Followbar Pin, place the Followbar
into the bender. See page 5 for the correct way to install the Followbar. Lightly spray some lubricant on the outside of the tubing
so that the tubing will slide through the Followbar easily. Any spray lubricant works well. If you are bending tubing with a wall
thickness of .065" or thinner you may want to skip the lube entirely. This will help the followbar stick to the tubing during ratchet
repositioning and generally helps prevent wrinkling. Make sure all pins are completely seated in their holes. Failure to do this
may cause damage to the bender links or worse yet the operator may slip and fall.
Place the 1" x 2" box tube handle over the Swing Lever making sure the Handle is as far forward as possible on the Swing
Lever. Rotate the Swing Lever fully counter-clockwise. Engage the Rachet onto the outer 3/4" drive link spacer tube. Lightly pull
on the handle to preload the tubing. Do not pull hard enough to actually bend the tubing. Using a free hand, loosen the degree
plate nut. Rotate the degree plate until the die's pointer is at 0 degrees and then hand tighten the nut to secure it into position.
Now you're ready to bend. Pull on the handle in a clockwise direction until the Swing Lever cannot rotate any further. Return the
Swing Lever to the starting position. Initially release the Ratchet easily so as not to move the tubing and minimize spring back.
Reengage the ratchet and pull again. When the last Ratchet tooth is reached, return the Swing Lever to its starting position.
Remove the 7/8" Drive Pin and rotate the Drive Links counter-clockwise until the Drive Pin may be reinstalled through another
hole in the Bending Die. Be careful not to move the tube. Now repeat the above bending sequence until the desired degree of
bend is obtained. To release the tubing from the bender, remove the handle from the Swing Lever. Insert it diagonally through
the 3/4" drive link spacer tubes and pull counter-clockwise. The Followbar will release its grip and the tubing may be removed.

 

WITHOUT DRIVE HOLES:
These dies typically have a center line
radius of less than 3". Because the radius of
the die is so small, drive holes cannot be
drilled into the die. This does not present a
problem as the tube sizes for these dies is of
relatively small diameter and is easily bent.
The ratchet is not used.
Die installation procedure:
Swing the ratchet assembly out of the
way as shown below. Place the forming die
into the bender. Place the tubing to be bent in
the bender and using the 5 1/4" long drive pin
(not the shorter U-Strap pin that is usually
used) install the U-strap. If desired, tighten
the U-strap bolt to secure the tubing to the die.
This is not mandatory and may be omitted if
the tubing shows no signs of slipping through
the die while bending. Now install the followbar being sure the word 'TOP' is facing up. Rotate the drive links until their front edge
pushes directly on the U-strap pin as shown in figure 6. Place the handle diagonally through the drive links' two 3/4" spacer tubes.
Lightly pull on the handle to preload the tubing. Do not pull hard enough to actually bend the tubing. Using a free hand, loosen
the degree plate nut. Rotate the degree plate until the die's pointer is at 0 degrees and then hand tighten the nut to secure it into
position. Now, simply pull the handle and observe the pointer until the desired degree is reached.

 

EXAMPLE BEND
 
The first thing you need to do is to determine the actual starting location of a bend produced by the Bending Die you installed
in the bender. This can vary between die sets and must be checked for every die set purchased. In the below example we are
using 1 1/2" O.D. tubing and a Bending Die with a Center Line Radius of 6 1/2".
Here's the procedure:
A) Place a piece of tubing (app. 2 1/2' long) into the bender so that exactly 12" extends out from the edge of the die to the
end of the tubing when the tubing is fully seated in the Bending Die's groove. Place a little bending pressure on the tube
so as to seat the tubing in the Bending Die. Not enough to start bending the tubing just enough to seat it in the groove.
NOTE: If you lay a small length of tubing in the groove of a Bending Die you will notice the tubing does not seat to the
bottom of the groove. The Bending Dies
are deliberately machined this way so
that during the bending operation a side
force is developed in the tubing. This
helps to reduce flat spotting and wrinkles.
B) Using a Black Magic Marker mark a line
on the tubing precisely at the edge of the
die. See figure 7.
C) Bend the tube to an exact 90 degrees.
Use a carpenters square to check the
angle. You will have to overbend the tube
a little to account for springback. How
much to overbend will come with practice.
If you overbend the tube a little don't worry.
Because cold worked steel has memory,
you can place the tube in a vise or anything
else that will retain it, and simply unbend
it. Obviously this only works for small
amounts of overbend. If the tubing is
underbent, it will be necessary to put it
back into the bender.
D) With the tube bent correctly to 90 degrees
locate the actual start of the bend. To do this, measure from the end of the tube to the far end of the 90 degree bend.
In the example in figure 8 this came out at 20 1/4". Subtract 6 1/2" for the centerline radius (CLR) of the Bending Die,
another 3/4" for the radius of the tubing not seated in the die, and 1/8" for springback. (Substitute the CLR and tube radius
to match your die set). The 1/8" figure for springback is an approximation, not an exact figure. However it is usually very
close to the real thing and may be used without worry to determine the actual starting location of the bend. So:
 

 

Now subtract from the 12 7/8" the original 12" we had
marked earlier and you find that the bend will actually
start 7/8" in from the edge of the bending die. Now we
know for example, if we want 40" from the end of the
tubing to the start of the bend, we must subtract 7/8"
from 40" and set the tubing 39 1/8" from the edge of
the Bending Die.
Another example, you want 36" from the bottom to the
top of a rollbar. Tube size is 1 3/4" and you have an
actual bend start 1/2" inside of the Bending Die's edge.
The CLR of the Bending Die is 7 1/2". So: 36" - 1/2"
(Actual Bend start) - 7 1/2" (CLR of die) - 7/8" (Half of
the tubing diameter) - 1/8" (Springback) = 27". Set the
tube 27" from the edge of the Bending Die and make
the bend.

 

 
-
Example hoop :
Preparation is the key to making accurate bends. To make multiple bends in one section of tubing you will need a universal
protractor. The protractor is then clamped, using a machinist v-block and a radiator hose clamp, to the tube. Make sure the pointer
indicates '0' before making your first bend. Also using a carpenter's level, make sure the tube is entering the bender level. On the
second bend if you turn the tube so that the pointer again reads '0' and the carpenter's level indicates the tube is level, both bends
will be on the same plane with no noticeable twist.

 

First step is to draw a sketch of the intended shape and all measurements. Figure 9 below is the desired hoop. The Bending Die
has a centerline radius (CLR) of 6 1/2". The tube O.D. is 1 1/2". We determined earlier, using the method described on page 4,
that the Bend Start measurement is 3/4" behind the edge of this particular Bending Die set.

1) Determine the total length of tubing needed. Using a calculator and the formula below let's add it all up.
6 1/2" (CLR of bend) x 90 (Number of degrees of bend) x .0175 = Length of tubing used in a bend.
Using the formula above we get 6 1/2" (CLR of bend) x 90 (Degrees of bend) x .0175 = 10.2375. Let's round this off to 10 1/4" inches
(10.250"). This is the amount of tubing used in the bend. We have two bends so we double this and get 20 1/2". Add to this the
straight sections and we get 20 1/2" (tubing in bends) + 27 (the center section) + 13 1/2" for the left upright + 13 1/2" for the right
upright = 74 1/2" of tubing needed. It's usually a good idea to leave a couple of inches extra on the end. Remember, it's easier
to remove tubing then to add it. So let's add 2" to 74 1/2".

 

2) We cut our tube to 76 1/2". It's generally easier to work from the center out when making two bends in a tube. Divide 74 1/2"
by 2 and our center point is 37 1/4" from the end of the tube. Place a mark on the tubing 37 1/4" in from one edge and mark the
tubing so you will know which side is the 37 1/4 side and which side is 39 1/4". Notice we didn't use the 76 1/2" measurement that
we cut our tubing to. This way we only have to cut 2" off one end of the finished tube instead of 1" off each end. The first bend
is made on the short 37 1/4" side.

 

3) Using the method described on page 4 we determine that the tube should extend 12 5/8" from the edge of the Bending Die.
Below is the equation from page 4.
20" (Height of hoop) - 6 1/2" (CLR of die) - 3/4" (1/2 of tube's dia.) - 1/8" (Springback) - 3/4" (Bend Start) = 11 7/8".
After making the bend we have half our hoop completed. The top of the bend is 20" from the bottom of the tube.

 

4) Now for the other bend. First we need to determine how much the tube stretched in the bend area. From figure 9 we see that
the tube should be 20 3/4" from the outside edge to our 37 1/4" center mark. However after measuring from our center mark to
the outside edge of the bend we now have 21" and not the planned 20 3/4". This 1/4" increase is due to springback and the tube
stretching in the area of the bend.
 
 
If we now repeated the second bend, using the same 12 5/8" from the end of the tubing + 2" for the extra tubing we allowed, we
would end up with a hoop 1/2" too wide. This is because the 1/4" stretch developed in the first bend will also be developed in the
second bend, giving us 1/2" total increase in width. Not a good deal if you only want a 40" wide hoop. So what's the solution. Actually
there is two ways to do it.

 

FIRST METHOD:
Look at figure 9 and notice the second bend starts at the top of the hoop and not at the top of the upright as the first bend did. Also
the start of the second bend is drawn as 13 1/2" from the center mark. If you take the 13 1/2" measurement and subtract the 1/
4" of growth that was developed in the first bend and another 1/4" to compensate for the second bend's growth you end up with
13". Subtract another 3/4" to account for the 3/4" Bend Start location on the Bending Die set and we have a final setting of 12 1/
4". Notice we did not subtract an 1/8" for springback. This is accounted for already in the 1/4" we added for the second bend's
growth. Set the tube so that the Bending Dies edge is exactly 12 1/4" from the center mark. Make sure the universal protractor
reads '0' and the carpenter's level is centered. As one final check you can also measure from the far side of the completed bend
to the edge of the bending die. See figure 10. This measurement should read:
40" (width of hoop) - 3/4" (radius of tube not in bending die) - 1/8" (springback allowance) = 39 1/8"
Make the second bend. Measure the height of the second upright and cut off the extra tubing we allowed for earlier.

SECOND METHOD:
The second method is basically the opposite of the first method. The second bend will start at the bottom of the upright and NOT
at the top of the hoop as in the first method and as shown in figure 10. We use the same method as used to bend the first bend
with a few exceptions. First calculate the starting point for the second bend as shown below:

 

20" (total height of hoop) - 6 1/2" (CLR of bending die) - 3/4" (Bend Start) = 12 3/4"

 

Add 2" to account for the extra tubing we allowed earlier. Also add the 1/4" growth developed in the first bend and another 1/4"
for the second bend. DO NOT ADD 1/8" SPRINGBACK. Once again this is already accounted for in the 1/4" growth of the second
bend. We end up with:

 

12 3/4" + 2" (extra tubing) + 1/2" (growth for both bends) = 15 1/4"

 

Set the tube's end at 15 1/4" from the Bending Die's edge. Make sure the universal protractor reads '0' and the carpenter's level
is centered. Make the second bend. Measure the height of the second upright and cut off the extra tubing we allowed for earlier.
Thank you for purchasing the Model 3 Tube Bender. Any further questions please call.
 
Copyright 2004 by J D Squared Inc.
 

 

 

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