The Project

My friend Gary bought this 1957 Porsche Speedster 30 years ago. He had good intentions of restoring it himself, but since he’s in the collector car restoration business, his customers’ cars always came first. He made some progress over the years, but a lot of work still remained.

The series of pictures I’m documenting here are of the rear body shroud, which had an impressive dent on the left rear quarter — inflicted about 35 years ago. I offered to help Gary make some progress on the Porsche, and in return he’s letting me copy the surface information of the whole body. My intention is to capture all of the Speedster’s surface and reproduce the panels in aluminum and steel. Building a complete set of 1957 Porsche Speedster body panels will be the featured project of my monthly 4-day metal fabrication class. But first I have to get the panels in shape in order to copy them.

The sandblasted rear body shroud below shows the dent from the outside and the inside. The dent was approximately 4 inches deep and 24 inches long.

I roughed it out using one of my delrin head shaping mallets on my super beater bag — 150 lbs of sand in that beast. It’s now my favorite bag and I’ll be offering them for sale on the website soon. My former student Chris stopped by and I roped him into helping me hold the rear body shroud while I roughed out the dent in about five minutes.

The Method

The purpose of this article is to shed light on the technique of proper dent removal. First: there is no magic, there is no one tool you have to have, and you don’t need five-plus years of experience. Nothing more than good information, good eyesight, feel, and most importantly patience and passion are required to get flawless results.

There are many ways to take dents out. Here are a few techniques that would work that I won’t be covering here:

Mobile planishing hammer — valid but requires the tool and possibly frame hoops for reach
Mobile English wheel — same drawbacks
Cut out the damaged area — correct on an English Wheel or planishing hammer and weld back in
Make a new panel — shape a new repair panel and weld it into the damaged area

The method I use: A simple, inexpensive technique with few tools that yields perfect results. Most people who work on their own collector cars don’t want to spend thousands on equipment. If that’s you, you’ll especially appreciate this approach.

Tools required: a shaping mallet, a dolly, a slapper, a fine cut file, a magnum magic marker, and a 9″ shrinking disc.

The Tools

Dealing with Stretching First

If the sheet metal is stretched more than 1/8″, it’s best to use a torch to bring those spots down before starting. In this case the metal wasn’t stretched enough to need it. The torch is excellent for quickly bringing very stretched areas back — heat the stretched spot to a dull red and whack it down with a body hammer. The red-hot metal becomes plastic and flows into itself, thickening and reducing surface area. After shrinking, lightly planish the area with a slapper and dolly. The shrinking disc will take it from there.

The Slapper and Dolly

The dolly is a Herbrand Tools dolly — they’ve been out of business for years. I bought it in 1967 from the Herbrand tool rep who came to my grandfather’s restoration shop weekly. It became my favorite body dolly. I use it about 90% of the time. It has a low crown on one side and a medium crown on the other, with very useful shapes on the ends and sides as well.

The slapper I made from a Duesenberg rear spring. It’s the perfect size and I use it far more than body hammers. I’ve yet to see a commercially made slapper with all the right features. I rounded all the working surface edges so it won’t scar a panel if you mistakenly strike at an angle.

The Magic Marker

Use a 5/8″ wide felt magic marker. I use markers instead of spray dye because they work better. The marker serves as both a high/low indicator and a lubricant for the shrinking disc. Without it the shrinking disc will scratch the surface and cause galling. With the marker you won’t have any problem — the disc also builds up a scum on its surface which further protects against galling. If you ever see sparks when using a shrinking disc, you’re galling the metal. Stop immediately and sand the buildup off the disc.

Also useful: a Baltic birch plywood 6″ diameter sanding disc with 220 stik-it paper on both sides. The round shape works best on most panel shapes to find highs and lows. I also use a German-made Pferd brand super-fine 20-teeth-per-inch file for the same purpose — it works slightly better than the sanding block. I rounded the edges so they don’t bite in. Little or no metal is removed with either tool.

The Shrinking Disc

The 9″ shrinking disc mounts on a 9″ angle grinder using a central hub support, a 9″ backing pad, and then the disc. The nut has a 7/8″ neck and a large flange — when mounted correctly the nut sits below the working surface of the disc. The disc is used running flat on the panel.

The concept goes back to at least the 1930s when bodymen used dull flex-back grinding discs as surface friction heaters. Master metal shaper Scott Knight created the first stainless steel shrinking disc in the early 80s. I came up with the smooth and safe style shrinking disc first and have been selling them worldwide for more than ten years. I also created the first smaller-diameter shrinking disc for small grinders. My discs are available in the tool section of this website.

Understanding What’s Happening in the Metal

Arrangement vs. Area

Think of a cross-section of the panel. At the top: a nice smooth flowing curve — that’s what the panel is supposed to look like. Below it: the roughed-out surface after banging out the massive dent. The slapper bridges two high spots and the dolly positions itself under the low area. When you strike with the slapper, you drive the two highs down and the dolly forces the low up. You’re ironing out the surface ruffles. I call this changing the arrangement.

Sheet metal is exactly like clay, just more stubborn. Instead of squeezing it in your hands, you persuade it with the slapper and dolly. I separate dent work into two concepts:

Arrangement change — 99% of removing a dent is returning the panel to its correct arrangement. This is the position of the metal, not the amount of it.
Area change — Stretching or shrinking changes the actual surface area of the metal. The original denting and roughing out probably added about 1% growth — not a lot, but it has to be corrected.

The Process Step by Step

Coat the surface with the magic marker
Sand or file lightly to reveal the highs (shiny) and lows (still black)
Place the dolly under a black low area
Slap the two shiny highs on either side
The black areas shrink in both area and depth
When a low is only about 20 thousandths of an inch deep, you’ll start to see shiny contact footprints where the dolly is making contact — confirmed by a ringing sound
Use those footprints to steer the dolly around the remaining low area
After slapping, lightly re-polish with the file or sanding block — the black area will have reduced
Once you’ve brought up a bunch of low areas, use the shrinking disc to shrink out remaining area change and iron the surface smooth

Caution: Don’t get carried away with the shrinking disc — you can easily over-shrink. If you do, just stretch it back out again with slapper-on-dolly compression stretching.

When you master this process it becomes genuinely fun. You’re no longer at the whim of the sheet metal — you’re in total control. There’s a real sense of accomplishment when you properly smooth damaged panels without reaching for body filler.

The Final Result

At my February coachbuilding class I had a chance to do more work on the rear body cowl. As part of the class — in addition to teaching panel making and TIG welding — I demonstrate the slapper, dolly, and shrinking disc technique so students can see the full process live.

This is how the dent looked 30-plus years ago when Gary first brought the car in.

When I last worked on the panel I had roughed out the massive dent and finished the left side, leaving the right side roughed out as a visual contrast. Below you can see the left side condition before the class session.

At the class I completed the left forward side. The results speak for themselves — no filler, no mud, just metal worked back to where it belongs.

I’ll continue using this rear body shroud as a teaching example until it’s completely smooth — factory condition or better. After that I’ll capture the surface information to make copies of the panels.

Looking to remove a dent from aluminum? Check out our comprehensive video on how to do it with simple hand tools: Aluminum Dent Removal Video

Tools Used in This Article

9″ Shrinking Disc — Pro Shaper smooth and safe style
Delrin head shaping mallet
Herbrand-style body dolly
Custom slapper (made from Duesenberg rear spring)
5/8″ felt magic marker
6″ Baltic birch sanding disc with 220 stik-it paper
Pferd super-fine file (20 tpi)
9″ angle grinder