Automotive Bodywork and Rust Repair

by Matt Joseph

  If you are working with larger

  Old body shop practice was to use panels, like whole bodies, hoods,

  36-grit, and even extremely coarse

  decklids, or doors, you should con-

  24-grit, abrasive papers for this pur-

  sider dip stripping as a method of

  pose. Open-coat abrasive papers in

  paint and rust removal. At one time

  the 60- to 80-grit range are best for

  there were many dip-strip tanks in the

  this purpose, and leave panel surfaces

  United States. Unfortunately, some of

  that do not require as much cleaning

  the operators of these facilities dis-

  Disc sanding works well to remove

  up to remove abrasive gouges.

  posed of their spent chemicals in irre-

  paint and rust from body panels. You

  There are many other varieties of

  sponsible ways, like dumping them

  have to be careful with this technique

  spinning devices—abrasive paper flap,

  into city sewer systems. Since much

  not to overheat metal and warp it.

  wire, and mesh-pad-type wheels, for

  of the paint dissolved in these efflu-

  Done properly, disc sanding is a slow

  example—that will clean metal. Some

  ents contained lead, many of these

  metal-cleaning method.

  of these can work on 41⁄2-inch grinders,

  facilities ran into regulatory prob-

  and produce very good results. Some

  lems, and were forced out of business.

  strippers will work, and aircraft-type

  of the plastic mesh discs sold for this

  There are still some dip strippers left,

  paint remover is a particularly good

  purpose work surprisingly well for

  and, depending on your distance

  way to do this job.

  paint and surface rust removal. One

  from one of them, this technique

  Disc sanding with abrasive paper

  great advantage that abrasive papers

  may be a good way for you to cleanse

  mounted on a 7- or 9-inch electric

  mounted on larger disc sanders (say, bodies and panels to bare metal.

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

  CLEAN I NG, MODE LI NG AN D CUT TI NG

  My experience with dip stripping

  metal. But they must be used slowly,

  tells me that this service can vary

  due to their potential to warp metal.

  greatly in quality and effectiveness

  This means a combination of a

  between vendors. Some systems use

  numerically

  low

  nozzle-to-target

  heated chemicals. Many of them use

  angle, low blast pressures, media-rich

  electrolytic action to enhance clean-

  mixtures with air, and/or long nozzle-

  ing. Some operators of these services

  to-target distances.

  are more careful about the chemistry

  Any of these approaches, or com-

  in their tanks than others. In sum, if

  With considerable patience, abrasive

  binations of them, makes the blast

  there is a reputable dip stripper rela-

  blasting works well to clean sheet

  removal of paint and rust from

  tively close to you, you should con-

  metal thoroughly. You have to be

  sheetmetal very slow. However, if

  sider this method of cleaning your

  careful to work slowly, or you will

  you are willing to exercise the

  metal panels. In most cases, stripping

  warp the metal. Media-rich

  restraint to do this, which is often

  a single door or decklid does not jus-

  air/abrasive mixtures, low numerical

  very difficult, you can blast sheet-

  tify driving any great distance to a

  blast angles, low blast pressures, and

  metal clean with good results.

  dip-strip tank. On the other hand, if

  long nozzle-to-target distances help

  The second downside of blast-

  you have a complete car to strip, or if

  to prevent distortion.

  cleaning metal is that it leaves it so

  you live near a dip tank, this method

  clean that any moisture in the air

  may be a valid approach.

  repair by what someone thought was

  tends to rust it almost immediately.

  Abrasive blasting, sometimes

  safe blasting. The only way to safely

  In dry environments this is a smaller

  called sandblasting, is another major

  blast sheetmetal is to do it very

  problem than in wet ones. In all sit-

  category of metal-cleaning technol-

  slowly. Soft or small blast media, like

  uations, blasted parts should be

  ogy. Blasting is a terrific method for

  soda and polystyrene beads, are very

  worked on quickly, re-cleaned, and

  cleaning metal if it is performed by a

  slow ways to clean metal. They do

  then painted or treated with a preser-

  skilled professional. In addition to

  not remove deep, pitted rust very

  vative immediately.

  getting metal metallurgically clean

  well, if at all, but they do avoid the

  (as the abrasive blasting industry

  warping hazard. Harder media, like

  Cutting Panel Materials

  claims for some blast media), this

  silica

  sand,

  tungsten

  carbide,

  approach leaves an excellent tooth

  aluminum oxide, and cold chilled

  There is no perfect, or best, way

  on finished metal. This means that

  copper slag, will produce very clean

  to cut sheetmetal materials. Different

  the surface will have nooks, crags,

  and crannies that will help paint to

  If you are lucky

  mechanically adhere to it.

  enough to have a

  There are two downsides to abra-

  good jump shear

  sive blasting to clean autobody panel

  like this one, you

  metal. The first is that blasting tends

  can make straight,

  to expand surfaces to which it is

  clean cuts in

  applied. Media, like glass bead, do

  sheetmetal almost

  this in the extreme. When you

  effortlessly. Hand-

  expand one side of a surface, but not

  cutting techniques

  the other, the metal tends to bend

  for this kind of job

  around the unexpanded side. Put

  are never quite as

  simply, it will warp. And, no, you

  good.

  cannot blast the other side to bring it

  back into proper shape. I wish that it

  was that easy.

  I have seen fenders and doors

  ruined beyond the possibility of

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

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  CHAPTE R 4

  A stationary hand shear, like this

  Beverly shear, is a great way to cut

  very accurate shapes into flat

  Aircraft snips are great for making

  sheetmetal. This type of shear is

  accur
ate cuts in flat sheetmetal, and

  throatless, so there is no limit to the

  work well on mildly curved surfaces.

  depth of cut that you can make with it

  They cut reasonably quickly and are

  Band sawing is a great way to make

  into panel steel.

  relatively inexpensive.

  accurate, smooth-cut lines in flat

  sheetmetal. Unfortunately, a good,

  metal-cutting band saw is an

  expensive piece of equipment.

  methods of cutting metal work best

  in different situations.

  If a straight line is required, it is

  best to shear flat metal in a metal

  shear. A stationary or hand shear is a

  very good approach to delicate detail

  work. Another possibility is using

  pneumatic and electric shears of vari-

  ous types. Tin snips and aircraft-type

  snips are good for small shearing jobs

  in flat and curved metal. Band sawing

  is a very good way to cut flat metal

  stock very accurately and quickly.

  Unfortunately, good metal band saws

  Air-driven saber saws are cheap and are capable of making accurate cuts in

  are quite expensive.

  contoured sheetmetal. They are the body shop standby for excising diseased

  Reciprocating pneumatic saws

  areas in panels.

  offer a very effective and inexpen-

  sive way to cut detailed lines in pan-

  builders. Electric hand shears are

  use because they spew crescent-

  els, and are particularly useful for

  also very accurate and fast for mak-

  shaped metal fragments from their

  cutting bad metal out of large, con-

  ing simple cuts.

  cut paths, all over creation. Find

  toured panels. High-speed abrasive

  Nibblers, both air and electric,

  some use for those fragments, and

  discs mounted in air grinders are

  have some application to cutting

  you may become wealthy and appre-

  another way of making accurate

  autobody metal, particularly when

  ciated by many. Hole saws and

  cuts. This method is favored by

  there is no direct entry to begin a

  punches are also options for opening

  many body shops and custom

  cut. Unfortunately, they are messy to

  up areas, so that you can use other

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

  CLEAN I NG, MODE LI NG AN D CUT TI NG

  Carbide burrs mounted in air die

  grinders, like the angle grinder shown

  here, are a terrific way to fine tune

  High-speed abrasive disks, mounted in air die grinders or muffler cutters, are

  metal edges for fit-up to other edges.

  great for cutting into contoured panels, but are pretty much limited to cutting

  These tools are surprisingly

  straight lines.

  inexpensive.

  This type of electrically driven hand

  shear cuts metal quickly and

  accurately, and is not limited to flat

  Plasma arc cutters cut very quickly, but lack the accuracy of mechanical

  surfaces. Air-driven versions of this tool

  methods of cutting metal. They work well on curved surfaces, and leave

  lack sufficient torque, and do not work

  weldable edges. Despite the intense heat that they generate, they cause little

  as well as electrically driven versions.

  distortion in metal because their cutting heat is contained very locally.

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  CHAPTE R 4

  cutting methods when interior cuts

  in metal panels are required.

  Plasma arc cutting is a high-tech

  method of severing sheetmetal. It is

  very fast, and leaves edges that are

  still weldable, unlike cutting with an

  oxy-acetylene torch. However, the

  lack of fine control of plasma-arc cut

  lines restricts the use of this method

  to situations where fine accuracy

  along cut lines is not required.

  Fine adjustments to metal edges

  These wire patterns almost look like art, but are really forms that are

  are often made with die grinders and

  incredibly useful for checking metal as it is formed into faithful replicas of

  files. This is particularly true when

  original parts. They are also quite durable.

  parts are being fine-tuned for tack

  welding and welding. High-speed

  the actual forming process. In either

  electric and pneumatic die grinders

  case, these models and forms serve as

  are also very useful for making these

  standards against which to check the

  kinds of fine adjustments.

  fidelity of the metal that you are

  forming. Sometimes, the metal is

  Getting Shapes and

  intended to replicate some original

  Contours Right

  part, section, or feature of a vehicle.

  Other times, it is designed to guide

  There are many ways to create

  the construction of a custom part or

  three-dimensional models and forms

  panel for an entirely new fabrication.

  for sheetmetal objects. These may

  Very advanced prototype shops

  vary from those that just indicate

  have computer-driven systems and

  dimensions to be followed, to those

  hardware that can sense existing or

  that can be used, almost like dies, in

  conceptual shapes, turn them into

  Paper templates can be made as

  numerical coordinates, and automat-

  drawings or as three-dimensional

  ically form them in various plastic

  representations of original metal. This

  materials or shave them out of

  paper model is a combination of

  blocks of clay. This kind of capability

  drawing and contouring to capture

  is wonderful to behold, but presently

  the shape of a part that will be

  it is way beyond the scope or needs

  formed in metal.

  of most sheetmetal projects that

  don’t involve automobile prototyp-

  ers have developed various modeling

  ing and manufacturing.

  methods in paper, both with flat

  My favorite method of transfer-

  drawings and by forming the paper

  ring most simple contours and

  into three dimensions. Clay and

  dimensions from existing shapes to

  wooden-buck modeling are steps

  models is to use number-12 copper

  beyond that.

  Good, old metal files are great for

  electrical wire, or grids made from

  When I want to model all of a

  straightening cut lines in metal edges,

  this wire. Examples of this technique

  shape in three dimensions, I usually

  and for removing burrs and other

  are shown in Chapter 3 and Chapter

  use the old egg crate modeling con-

  imperfections. They can be used in

  12. Every shop has its own favored

  struction. It is relatively quick, easy

  combination with handheld edg
e

  methods of modeling shapes. Wire

  to do, accurate, and inexpensive in

  deburrers to produce very clean edges.

  forms are a favorite with many. Oth-

  material costs.

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

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  Making an Egg Crate Pattern/Model

  We created this egg-crate

  pattern to physically

  represent the dimensions

  of the hood scoop shown

  in the next photograph. It

  is useful for guiding

  metal forming to the

  correct dimensions. The

  footprint diagram of the

  The actual shape that will be

  part and its recorded

  transferred to, and cut out of,

  measurements are to the

  each rib is captured with a plastic

  right of the model.

  profile gauge, for transfer to each

  rib. This technique results in a very

  The strange-looking items in the photo between the two is a matter of personal accurate pattern.

  are patterns for the hood scoop on a

  preference.

  1953 Aston-Martin DB2. This technique

  In making this form, the first step was

  of creating a three-dimensional model

  to lay out strips of 1⁄4-inch tape in a grid along

  provides a pattern that is useful as a

  the hood scoop. Note that the tape posi-

  guide and check for fabricating this

  tions were identified by letters and numbers

  shape. As the shape is formed in metal,

  to keep confusion to a minimum when the

  the pattern can be laid over it to check fit,

  contours that they represented were trans-

  and to indicate changes that need to be

  ferred to cardboard and assembled as an

  made. This type of pattern also can be

  egg crate. The marked edges of the tape

  Poster board is an adequate

  made in a convex format, in contrast to

  (forward or rear edge, and left or right edge)

  material for making this kind of

  the concave format shown. The choice

  were marked to indicate which edge was

  model. It has the advantage of being

  used, and became the indexing points for

  very easy to cut accurately. Some

  the parts of the egg crate model. Dimen-

  plastic materials are a little stronger,

  sions of the footprint of the scoop were

  and metal is even more durable.

  taken and transferred to a sheet of paper.

  A profile gauge was applied to the

  indexed against the front of the hood

  contours of the scoop, and the profiles

  scoop to confirm its exact height as com-