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newSchoolWorks.com › VoTechWorks › Transportation › Auto Body & Collision › Panel Repair and Replacement › Lesson 2
TRN-AUTO25-03 · Lesson 2 · 16.5 clock hours · demo

Hand Tool Fundamentals: Hammers, Dollies, and Spoons

Objective. Students will correctly select and apply body hammers, dollies, and spoons to work steel panel damage using hammer-on and hammer-off dolly techniques without adding new distortion.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a certified examiner or master technician in the trade or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

What These Tools Actually Do

Body hammers, dollies, and spoons are the core hand tools of collision repair. Used correctly, they move metal back toward its original contour without thinning, cracking, or work-hardening it beyond use. Used carelessly, they add distortion faster than they remove it. The goal every time you pick up a hammer is controlled force in the right place — nothing more, nothing less.

Body Hammers

All body hammers share a light head (typically 10–16 oz) and a flexible handle that absorbs shock and gives the technician feedback through vibration. The three you will use in this lesson are:

Hold the hammer near the end of the handle — not choked up near the head. A relaxed grip lets the handle flex and transfers force efficiently. Let the hammer rebound naturally; fighting the rebound wastes energy and bruises the metal.

Dollies

A dolly is a hardened steel block held against the back side of a panel. It acts as a portable anvil. Common shapes and their uses:

Press the dolly firmly against the back of the panel so it does not bounce. A dolly that chatters transfers uncontrolled energy and stretches metal.

Two Fundamental Techniques

Hammer-On Dolly

The dolly is held directly behind the point of the hammer blow. Striking the high spot drives it down while the dolly supports and slightly rebounds the metal from underneath. This technique is used to raise low areas when the dolly is also targeted beneath the low spot, and it can slightly stretch metal, so use it conservatively. It produces a smoother result on broad, gradual dents.

Hammer-Off Dolly

The dolly is offset — held under a low area adjacent to where the hammer strikes a high spot. The hammer blow drives the high spot down; simultaneously the dolly's reaction pushes the low spot up. This is the more commonly used technique because it moves metal without significant stretching. Work in a pattern around the damage, gradually reducing the high and low areas until the surface levels.

Body Spoons

A spoon is a long, flat or curved tool used for leverage and for reaching damage where a hammer or dolly cannot fit. Slide the spoon behind a crease or behind a inner structure, position it against the back of the damaged area, and tap the spoon's exposed end with a hammer. The leverage lifts the dent indirectly. Spoons also spread hammer force over a larger surface area, reducing the chance of adding new marks. Never strike a spoon so hard that it slips — a flying spoon is a serious injury hazard.

Working Order: Roughing to Finishing

1. Assess the damage. Find the primary impact point and trace the stress lines outward.

2. Rough out from the outside edges of the damage inward, not from the center. Working center-first locks the edges.

3. Switch to hammer-off for the final passes. Light, overlapping blows, listening and feeling for progress.

4. Use a pick only for isolated low spots. A single controlled pick blow is better than repeated strikes.

5. Shrink high spots with the pick tip — a sharp tap on a high spot upsets the metal and reduces the stretched area.

Guide Coat Check

Once the panel feels close to flat, apply a light, even mist of dark aerosol primer (guide coat) across the surface and let it flash dry (about one minute). Lay a metal straightedge diagonally, then at 90°, then lengthwise across the panel. Any high spot rubs the guide coat off; any low spot retains it as a dark hollow. Continue working until the guide coat cuts evenly across the entire area. This gives you an objective measurement to replace guesswork.

Safety Requirements

Key terms8

Hammer-on dollyTechnique in which the dolly is held directly behind the hammer blow, providing direct support and slight rebound to move metal in both directions simultaneously.
Hammer-off dollyTechnique in which the dolly is offset beneath a low area while the hammer strikes an adjacent high spot, raising the low and lowering the high without significant metal stretching.
Pick hammerA body hammer with a pointed tip used to lift isolated low spots from the front of a panel or to shrink small stretched high spots with a controlled pinpoint blow.
Body spoonA long, flat or curved tool inserted behind a panel to reach damage indirectly; the exposed end is struck with a hammer to apply spread, controlled leverage.
Guide coatA thin mist of dark aerosol primer applied over a repaired surface; high spots rub off when a straightedge is drawn across, and low spots retain the dark color, revealing surface irregularities.
Work hardeningThe increase in hardness and brittleness that occurs in steel when it is repeatedly struck or flexed, making further shaping more difficult and increasing the risk of cracking.
High spotAn area of a panel that sits above the surrounding original contour, often caused by metal being displaced upward or outward during an impact.
Low spotAn area of a panel that sits below the surrounding original contour; identified by guide coat pooling dark or by a straightedge rocking over adjacent metal.

Worked examples3

1. After roughing out a dent, you lay a 300 mm straightedge across the panel and observe that it rocks. The gap under the straightedge at the center measures approximately 3 mm. Your target is within 1.5 mm of flat. How much more depth must you reduce, and is the panel within spec?
  1. Record current deviation: 3 mm gap at the center.
  2. State the specification: the surface must be within 1.5 mm of flat.
  3. Calculate remaining deviation to remove: 3 mm − 1.5 mm = 1.5 mm still needs to be worked out.
  4. Conclude: the panel is NOT within spec yet; further hammer-off dolly passes are required.
Answer: The panel is 1.5 mm outside the 1.5 mm tolerance and requires additional working before it passes the straightedge check.
2. You apply guide coat and pull a straightedge across the panel in three directions. One pass at 45° shows a dark stripe 40 mm wide still holding guide coat. A pass at 90° to it shows the same stripe. What does this pattern tell you, and what technique should you use next?
  1. A dark stripe that appears in both diagonal passes indicates a low spot (the guide coat is not being rubbed off because the straightedge bridges over it).
  2. The overlap of both passes at the same location confirms it is a true low area, not a long groove.
  3. A low spot that is isolated and small is best addressed with a pick hammer blow from the face side, or by repositioning the dolly directly under the low spot and using a light hammer-on blow.
  4. After the blow, reapply guide coat and re-check before making additional strikes.
Answer: The pattern indicates a low spot approximately 40 mm across. The correct next step is a controlled pick or careful hammer-on dolly technique targeting that specific area, followed by a new guide-coat check.
3. Your practice panel is 250 mm × 300 mm. After working it, you check with a straightedge across the 300 mm length and find a 2 mm high spot at one end. You then check across the 250 mm width at the same location and find a 0.8 mm deviation. Which reading controls whether the panel passes the 1.5 mm spec, and why?
  1. The specification states the surface must be within 1.5 mm of flat — this applies in every direction.
  2. The 300 mm lengthwise check shows 2 mm deviation, which exceeds 1.5 mm.
  3. The 250 mm widthwise check shows 0.8 mm deviation, which is within 1.5 mm.
  4. The panel fails because both directions must be within spec; the worst-case reading (2 mm) controls the pass/fail decision.
Answer: The 2 mm lengthwise reading controls. The panel fails the check and requires additional working in the lengthwise direction until that deviation is reduced to 1.5 mm or less.
In class: Instructor demonstration on a steel hood skin: hammer-on and hammer-off dolly techniques, pick hammer use for shrinking high spots, and spoon leverage for indirect damage access. · Students practice hammer-on and hammer-off techniques on pre-dented 20-gauge steel practice panels clamped in a panel vise, cycling through at least four hammer/dolly combinations. · Peer-check exercise: students use a metal straightedge and guide coat (light spray of dark aerosol primer) to reveal remaining highs and lows, then continue working until the guide coat is cut evenly.
Materials: Body hammers (picking, finishing, bumping), dollies (heel, toe, comma, general-purpose), body spoons, 20-gauge steel practice panels, panel vise or metal stand, metal straightedge, guide-coat spray, safety glasses, gloves
Check: Practice panel surface is within 1.5 mm of flat verified by straightedge; no new distortion introduced; instructor observes correct grip, stance, and blow force before signing off.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Collision repair fundamentals / non-structural panel repair
1. When using hammer-off dolly technique, where is the dolly positioned relative to the hammer blow?
Collision repair fundamentals / non-structural panel repair
2. A technician notices a small, isolated high spot that resists leveling with a finishing hammer and general-purpose dolly. Which tool is BEST suited to shrink that specific high spot?
Collision repair fundamentals / surface preparation
3. Guide coat is applied to a repaired panel and a straightedge is drawn across it. The guide coat is removed cleanly in most areas but remains as a dark patch in one location. What does this indicate?
Workplace safety / PPE
4. Which personal protective equipment is the MINIMUM required when hammering on steel practice panels?
Collision repair fundamentals / non-structural panel repair
5. A student is working a dent and starts hammer blows at the very center of the impact point. What is the likely result of this approach?
Collision repair fundamentals / non-structural panel repair
6. What is the PRIMARY reason a body spoon is used instead of a dolly in some repair situations?
Collision repair fundamentals / quality inspection
7. A practice panel measures 2.8 mm out of flat after initial working. The pass/fail criterion is within 1.5 mm of flat. Approximately how much additional deviation must be removed for the panel to pass?
Collision repair fundamentals / materials and metallurgy
8. Repeated heavy hammer blows in one area cause the steel to become increasingly resistant to movement and feel stiffer. This is BEST explained by which metallurgical effect?
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