Automotive Bodywork and Rust Repair

by Matt Joseph

  moved most of the metal to level. A little

  It remained to disc sand the entire

  both types. There are also specialty

  more picking and filing followed. This

  area around and between the dents with an

  files, like laterally concave and con-

  revealed that the damage was completely

  80-grit disc, and then to scuff the area with

  vex, and lengthwise convex (“banjo”)

  removed, and that the panel crown around

  an 80-grit DA random-orbital sander. This

  files. As well, there are specialty file

  and between the two dents was consis-

  achieved a surface that was smooth, and

  holders for particular jobs. The most

  tent and correct.

  that had good tooth for primer adhesion.

  useful general-purpose holder is a

  flexible metal rig that allows you to

  custom contour files by adjusting the

  holder. This is important for working

  with different crowns, and in some

  situations where access is a problem.

  The instructions for using body

  files are based on time-tested methods

  of filing, and are designed to optimize

  both revealing depressions in metal,

  After the first picking

  and leveling it. The first rule is to

  5

  operations, the repair area

  The repair area was now

  always file toward the flattest crown in

  6

  was filed with a flat body file

  smoothed with a disc sander,

  a panel. This reveals low spots as voids

  mounted in a flexible holder. Most

  loaded with 80-grit paper. This

  in filed metal, while preventing the file

  of the metal came level at this point,

  removed most of the scratches

  from skipping over features of the

  but some additional picking and

  resulting from the paint removal

  panel, like crown changes, as might

  re-filing were required to completely

  and filing operations. Note the

  happen if you fail to file toward low-

  remove the dents, and to give the

  almost flat position of the sanding

  crown areas.

  panel a consistent contour.

  disc for this procedure.

  Your filing stroke should use as

  much of your file’s length, in contact

  with metal, as is practical. As you

  file, there are two motions that

  should be used, beyond pushing the

  file forward and away from you.

  The first is to slide it sideways,

  about 15 to 20 percent of the dis-

  tance that you push it forward. This

  must be done smoothly, or gouging

  may occur. If you see tooth gouges in

  The filed panel looked like

  the metal, you are doing something

  7

  this. Note the filing scratches

  After a scuff sanding with

  wrong. The second motion amounts

  8

  in the repair area. This repair

  80-grit paper in a dual action

  to a subtle shift of force. It is to rock

  required so little filing that there

  (DA) orbital sander, the repaired

  the file from its front (toe) to its back

  was question whether the repaired

  surface was smooth and had good

  (heal) as you push it away from you,

  panel had any badly thinned areas

  tooth to hold primer. The

  forward and sideways.

  or spots.

  completed repair is shown here.

  Since, as a child, you doubtless

  mastered the trick of rubbing your

  tummy in a circular motion with one

  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

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  CHAPTE R 7

  hand, while patting the top of your

  made because sharp looks purposeful

  side with their fingers, until it is in

  head with the other hand, the filing

  and sexy. After all, stiletto heels and

  the right place. Another locating

  motions that I describe here should

  sharp

  features

  of

  the

  human

  technique is to follow the hammer

  come to you as, well, kid’s stuff. If

  anatomy are said to convey sexual

  under or behind the panel and sense

  they don’t, hours of practice certainly

  appeal and power. However, in pick

  where it is located in relation to the

  helps to fill any gaps. This combined

  hammers, very sharp items are more

  side that you can see. This works for

  filing motion is important and well

  useful for assault than for serious

  locating where to hit metal up. How-

  worth mastering. Once you do, it

  body work. If very spiked pick-ham-

  ever, it leaves the problem of hitting

  should quickly become natural.

  mers have any good application, it is

  exactly the spot that you have identi-

  The sideways file shift should be

  for very fine work; and then, only in

  fied. You might be amazed at how

  alternated from one side to the other.

  the hands of very highly skilled and

  lost that spot can become, between

  Say that you start by filing forward,

  seasoned metal workers.

  nesting a hammer on it, and then

  and shifting your file to the left. You

  That first problem, locating the

  swinging the hammer away from it

  may repeat this stroke a few times.

  place to raise metal, amounts to

  and then toward it again. Several

  Then, you should begin filing the

  translating where you know a low

  short, light strokes work best for pick-

  same area to the right, from the point

  spot is from the side of the metal that

  ing. A short stroke presents less

  where your earlier file strokes ended.

  you can see, to the one that you can-

  chance of missing your spot. And if

  In this way, you cover an area of

  not. There are body workers who do

  you do miss it, a short stroke does less

  maybe 1 foot x 3 to 5 inches, always

  this by hitting tentatively with their

  damage than a more powerful one.

  filing toward areas of lower crown.

  pick hammers from the backs of pan-

  After you gain pick hammer

  els, and sensing the hit on the other

  experience, you will be able to find

  The Art of Pick Hammering

  Here is one of those confidence

  builders. The first time that you try to

  use a pick hammer, you will, almost

  certainly, make a complete mess of it.

  I know that I did. This is because

  once their function is explained, peo-

  ple expect pick hammers to be mira-

  cle tools that naturally find low

  spots, and apply just enough hit to

  raise them to the perfect level for fin-

  ish filing. Sadly, to date, no such pick

  hammer has been invented.

  The first problem is that without


  some experience in the matter, it is

  frustratingly difficult to hit exactly

  the right spot with a pick hammer.

  That spot is usually on the other side

  of the panel from the one at which

  you are looking, so you are hammer-

  ing toward yourself. The second

  problem is that people tend to

  choose pick hammers that are far too

  This pick-hammer assortment has just about every device that you will ever

  sharp for what they are trying to

  need for picking work. The sharp, pointed one (top) has limited application,

  accomplish. I suppose that these pre-

  mostly for very fine tuning operations. The bottom three picks cover most

  dictably bad hammer choices are

  work to raise small low spots.

  66

  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

  M ETAL F I N I S H I NG

  the right spot on the other side of a

  panel fairly quickly, as a result of

  increasing your hand/eye coordina-

  tion. It is still a good idea to give

  the identified spot a light tap and

  feel its location through the metal,

  to confirm that it is correct. You

  will learn to see the metal rising

  each time that you hit it with your

  pick hammer. This allows you to

  make small adjustments in your

  hammering position, as you moni-

  tor your results from the other side

  of the panel. Always remember that

  you are trying to move metal just a

  few thousandths of an inch, and

  that you can correct some inaccura-

  cies in your picking in the filing

  stage that follows it. Many small,

  incremental hammer strokes do the

  job far better than a few heavy

  ones, and involve much less risk to

  the panel.

  Left to right: 9- and 7-inch electric disc sanders. Right: a 7-inch pneumatic disc

  Once you get the hang of picking

  sander. Electric sanders are preferred for metal finishing, because they have

  metal up, it is easy to get carried

  more torque. Note the warped disc on the middle sander. It will cause

  away, and to try to raise it to

  chattering and skips if its disc is not changed for a flat one.

  Himalayan heights. This is unneces-

  sary and it is destructive. To level

  The Disc Sanding Alternative

  body work is done with 7-inch units,

  metal, you need to pick up low spots

  with either rubber or fiber backings

  to a point just above panel height.

  After you have mastered the tech-

  behind the abrasive discs. When disc

  This allows you to file it perfectly

  niques of using body files and pick

  sanders are used for paint removal,

  level. If you raise metal beyond that

  hammers to level metal, the brave

  an open-coat abrasive disc is pre-

  point, when you file, you need to

  new world of disc sanding awaits

  ferred. When they are employed

  remove more metal than is necessary

  your discovery. Disc sanding offers an

  in metal finishing, closed-coat,

  to get things level. Always stop pick-

  alternative to body filing, but comes

  resin-bonded abrasives are best. The

  ing just after you achieve level, and

  with several cautions and warnings.

  36- and 50-grit sizes are appropriate

  let your body file or sander do the

  Disc sanding tends to be much faster

  for metal finishing with a disc sander,

  rest. You make this determination by

  than body filing and, for that reason,

  while 50-, 60-, and 80-grit sizes have

  running your finger tips over the

  it can damage a panel much faster

  applications for the final smoothing

  spot that you are picking. It is a good

  than filing it. The degree of difficulty

  of metal, after it is leveled.

  idea to put a smooth, clean rag or tis-

  in using a body file or disc sander is

  The first phase of using a disc

  sue under your finger tips when you

  about the same. Which technique

  sander for metal finishing is the dis-

  do this. That prevents the oils and

  you choose is largely a matter of per-

  covery phase. It involves disc sand-

  moisture on them from making your

  sonal preference. Many body metal

  ing metal surfaces so that the sander

  fingers grip, drag, or grab on the

  workers use both techniques, each in

  skips over depressed areas in a way

  metal as you feel it, and gives you a

  specific situations or in sequence.

  that reveals their presence.

  much better sense of the topography

  Disc sanders come in various

  Proper disc sanding technique,

  of what you are feeling.

  powers, speeds, and disc sizes. Most

  in the discovery phase of the

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  CHAPTE R 7

  Disc

  sanding

  for

  discovery

  should leave a series of swirl marks,

  or shiny paths. Any voids or dull

  spots in these paths are low spots.

  High spots may leave visible low

  voids around them. However, if they

  are not very high—not high enough

  to need to be hammered down—

  they will be ground off by the disc

  sander as it passes over them,

  thereby ceasing to be a problem.

  The cycle of leveling with a disc

  sander and pick hammer is the same

  as for a pick hammer and body file.

  Sanding identifies low spots and

  removes most high spots. Hammer-

  ing, as necessary and preferably with

  a low-crown hammer, drives down

  the high spots that are not removed

  by sanding. Hammering, usually with

  a pick hammer, picks up low areas.

  Occasionally, when low areas are rela-

  The final procedure in metal finishing is to disc polish the metal with 50-, 60-,

  tively large, they need to be driven up

  or 80-grit abrasives. This gives it a sheen that makes it easy to spot dimen-

  with a highly crowned hammer. As

  sional deviations. I always dull that finish with a DA orbital sander, for better

  with filing, the hammering and sand-

  paint adhesion.

  ing operations are repeated until the

  panel is level and continuous. Also, as

  operation, is to hold the abrasive disc

  sander, as you reverse its direction,

  with filing, disc sanding removes

  against the metal with moderate

  but that is clumsier than slightly lift-

  material and cannot be repeated to

  pressure, tilted about 15 degrees

  ing it to reduce the pressure on its

  the point of excessively reducing the

  away from it, and toward you, so

  contact edge. When travel resumes,

  thickness of a panel.

  that the sanding disc’s edge bends to

  in t
he opposite direction from the

  The 36- and/or 50-grit abrasives

  contact and cut a narrow swath of

  just completed stroke, the leading

  used in the discovery and leveling

  surface, say 1 to 11⁄4 inch wide. The

  edge of the sander should be raised,

  phases of disc sanding leave surfaces

  sander is moved sideways, and held

  just slightly, in the new direction of

  that are too rough to complete the

  mostly laterally flat to the panel,

  travel, as it was before.

  metal finishing phase of panel work,

  with a very small amount of tilt

  It is critical that the sander

  although 50-grit abrasives are some-

  toward the direction of sideways

  always be in motion on the metal.

  what usable for this purpose. Before

  travel. At the end of each lateral

  While it is running, it can never stay

  metal finishing is complete, the

  stroke, as the sander’s direction is

  in one spot. If it does, and if you are

  metal must be smoothed for paint-

  reversed, it is moved the width of its

  lucky, you will only overheat the

  ing. Although filling follows metal

  cut swath, up or down. When the

  metal where it dwells, with a very

  finishing, it is bad practice to leave

  sander’s lateral direction is reversed,

  good chance of gouging it. If you are

  final smoothing for that stage of this

  it should be lifted slightly to avoid

  not lucky, you can burn through the

  work. It should be the last part of the

  dwelling too long on the area where

  metal. A telltale dark bluing of the

  metal finishing operation. That

  the reversal of direction takes place.

  metal surface under the disc contact

  means that when metal finishing is

  You also can accomplish this by

  patch will warn you that you are

  completed, there should be few, or

  untriggering and retriggering the

  burning the metal.

  no, ridges or sanding marks that

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  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

  M ETAL F I N I S H I NG

  need filling. It also means that sur-

  should be slightly rounded, to keep

  in a fraction of a second. However, a

  faces are not so smooth that they

  them from tearing apart too easily in

  shaped, sided disc presents different

  lack the tiny nooks and crannies that

  use.

  radii of its shape to the metal as it

  help paint to mechanically adhere to

  In the final stages of metal finish

  spins against it, greatly reducing the