METAL BODY REPAIR - OD1653 - LESSON 1/TASK 1
(c) In direct hammering, the displaced metal will be pushed back to
its original contour, by using a dolly that matches the original contour
under the damage and striking the damage with a hammer. The dolly provides
support and prevents the undamaged areas from being pushed out of place. If
the metal is not struck squarely over the dolly, the metal will have no
support, creating damage which later must be corrected.
(d) Start by using light blows that show if the metal is being struck
squarely over the dolly block. Let the dolly lay in the hand and grip the
hammer loosely. When the first pimple has been eliminated, move to the next
one, until all have been removed. Two things occur with each hammer blow:
1 The hammer bounds of its own accord, making it ready for the
next stroke.
2 The hammer blow on top will drive the dolly block away from
the fender; the normal resiliency of the arm will bring it back, striking a
blow on the metal from underneath. These actions occur normally only if the
hammer and dolly block are held loosely. The importance of this springback
of the dolly becomes apparent as shown in indirect hammering.
(2) Indirect Hammering.
(a) Metal that has not been excessively hammered, displaced, or
stretched will have a tendency to return to its original contour of its own
accord.
This is due to the internal stress imparted to the metal by the
forming dies.
If the metal is prevented from springing back by other
strains imparted to it by additional bends or creases, the metal is restored
to normal contour by relieving whatever new stress is holding it out of
position.
(b) In bumping or dinging, this is accomplished by relieving the
stress with indirect hammering.
Figure 27 (on the following page)
illustrates a cross section of a damaged area in which sharp creases have
been formed all around an area and another sharp crease has been formed in
the low spot of the damaged area.
The procedure employed in indirect
hammering is to hold a dolly having the correct contour to match the
original contour of
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