JD Squared 3 - Page 6

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andtwoinserts.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
mold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.
 Notice that one insert is slightly angled. This angle is
calculatedandmachinedintothebackingblockto1/1000
of a degree from theoretically perfect for the tube size
and bend radius. This angle helps to support the tube or
pipeafter thepoint ofbend, greatly reducingattening.
Whenbending,theangledinsertwillalwaysbecloserto
theformingdie,andtheU-strapforthatmatter,thanthe
straight insert.
 A5/16"diameterrollpinisinstalledtoholdthefollowbar
in position while loading. When the followbar is in the
bender, theinsert groovesmust ride slightlylower than
the forming die's groove. This allows the followbar to RISE
underpressure.Ifthepinextendedtoofar,thefollowbar
would bind under pressure.
COMPLETEROUNDGROOVEDIESET
Below is pictured all of the components which make up a complete die set for round tubing or pipe. 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
attening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.
Followbar
Drive holes (5)
U-StrapPin
U-StrapBolt
Tube
Angled Insert
Straight Insert
Figure 10 - Die set components
U-Strap
1
2
Forming Die
- 5 -
Figure 9 - 1 1/2" OD Followbar Assembly
Rear
Angled
Insert
Front Straight
Insert
Backing
Block
1/2"
Locking
Bolts