Tips & Tricks From the Pros
This column is available for professionals in the metalshaping community to share some of their knowledge.
Tips from the Pros
For the Metalshapers Website
Photos by Terry Cowan
Hammers and dollies are simple looking, but it takes a good measure of
skill to use them properly. Most everyone has some experience using a
hammer, since the nail-driving style is so widely used for household
maintenance. Unfortunately, driving nails is not the same as smoothing
discuss hammers. The face is usually the ‘business’ end of a body
hammer, and it’s usually round, but sometimes square, and occasionally
you might find an oval-faced hammer. Probably the most important
characteristic of the hammer is the curvature and diameter of the face.
Diameters can range from 1 1/4" to 2", with around 1 5/8"
being my favorite. The face of most body hammers looks relatively flat,
but closer examination shows that they have a certain amount of curvature.
In fact, a hammer with a truly flat face would be nearly impossible to
use. The problem is, if you struck something with the face at even a
slight angle, the edge of the hammer would leave a ‘smile’ mark in the
metal that could only be removed by sanding, filing, or filling with lead
or plastic body filler. Most low-crown hammers have a face that with about
a 20” radius, but a few hammers are made with much more curvature than
this. The curvature of the hammer face has a lot to do with how well it
works, and it’s important to understand why. For general-purpose work, a
low-crown hammer face is the one used most often, but you may wonder why
some hammers have higher crown faces? There can be a variety of reasons.
When you strike metal with a hammer, the contact area of a low-crown face
might be around 5/16” across. This means that small area absorbs the
entire force of the hammer blow. If you use a medium crown hammer (6” to
10” radius), and hit with the same force, the contact patch might be
only ¼” across – or about 2/3 the area of the low-crown contact
patch. A hammer with a high crown face (2” to 4” radius) might have a
contact area only 3/16” wide, or about 1/3 the surface area as the
low-crown hammer. If you put the same force into a smaller area, the
effects of thinning and stretching will be exaggerated. On the rare
occasions when you need to stretch the metal a great amount, these medium
and high-crown hammers will certainly speed the work, at the expense of
leaving a more ‘textured’ surface (recall the look of a hand-hammered
copper vase to help visualize this). A more common reason to use a hammer
with a medium or high-crown face is to work into a concave area where a
lower-crown hammer face would only hit on its edges.
hammers come in a wide range of weights, from 12 oz. to 18 oz., or even
more. I prefer the lightest hammers for delicate work, but the heavier
ones may better suited for doing heavy collision repair. The handles are
usually made of wood, but fiberglass handles have been on the market for
many years, and a few people prefer the slightly more flexible ‘feel’
of the fiberglass-handled hammers. I think the fiberglass handles may be
more damage-resistant than wooden handles, as well. Although it’s rare
for a wooden handle to break, it can happen, especially if you are abusive
with the hammer. My personal preference is for the traditional wood
handles, but you might want to try them both.
While it’s nice to have a selection of hammer styles, I only occasionally use the end opposite the face. A pick hammer can be used to raise small low spots for metalfinishing, sometimes called ‘pick & file’ work. A cross-chisel or cross-peen hammer can be used to re-establish a peak, ridge, or crevice that has been damaged.
While we are on the subject of hammers, we should probably address so-called ‘shrinking’ hammers. There are two styles of these – the ‘meat tenderizing’ style, and the spiral-faced cam-action style.
The ‘meat tenderizing’ style has a gridwork of grooves embossed into the face, creating rows of sharply-pointed pyramids. While a hammer of this style may in fact ‘tighten up’ metal that is ‘loose’, it does so at the expense of putting a waffle-like texture in the metal.
plan to use plastic filler over the worked area, this texture won’t be
any problem, but if your goal is to metalfinish or polish the panel,
putting a waffle pattern on it is a step in the wrong direction. As for
the spiral-faced hammers with a cam that rotates the head as you strike,
I’ve tested them in every way I can think of, and my measured opinion
is that they don’t shrink metal, at least not any better that a
smooth-faced hammer would. Again, they put texture into the metal, which
may be undesirable. (I normally do everything possible to keep the metal
All of the US
made hammers I’ve seen are high quality, although the surface finish
will vary a bit from one manufacturer to another, but there are huge
differences in price. Surprisingly, some of the super high-end (and very
expensive) ‘Tool Truck’ hammers do not have the best surface finish,
even though they are forged from good steel. There are many imported
hammers on the market now, and the ones I’ve seen that come from
Germany and England are excellent, but the ones that come from China
aren’t so hot. They are made of low-quality metal, and the
‘balance’ doesn’t feel right to me. As much as I dislike these
cheap tools, you could probably make a case for buying a $20 set of 3
hammers and 3 dollies to find out what sizes, shapes, and weights of
hammers and dollies you like, and then buy some ‘good’ tools once
you’ve discovered your preferences. Don’t rule out swap meet and
Internet auction-site tools – there are some great bargains to be had
if you know what to look for.
probably even more varieties of dollies available than hammers! The
‘good’ ones weigh 2 to 3 ½ pounds, although there are certainly
some that weigh more and less. A dolly lighter than 2 pounds doesn’t
really provide adequate inertia to work with a medium or heavy hammer
blow, but a light, thin dolly just might fit into a ‘tight spot’
that no other dolly can. My heaviest dolly is the 4 ½ pound Martin
“Heavyweight” dolly, and I generally only use it in the rare
instance that its shape happens to fit a particular panel better than
any other dolly I have. It’s quite a strain for me to hold that dolly
at arm’s length for more than a minute or two!
European dollies are usually made from forged tool steel, and are quite
tough. All the Chinese dollies I’ve seen are made from cast iron, and
they dent much more easily than the ‘good’ ones. If you do much work
on aluminum you might consider having a special dolly or two that are
never used on steel, since any little nicks or gouges in the dolly would
leave marks in soft metals.
of having several dolly shapes is that the closer a dolly’s contour
matches the panel your are working on, the easier it is to get the panel
smooth by hammering. For a start, I’d suggest getting a dolly with a
large, low-crown face, such as either the Martin ‘Loaf’ or ‘Egg’
dolly, and a dolly with a totally flat surface, and one edge that’s
perpendicular to it. The low-crown dolly is the one I use for most of
the work I do, and the flat dolly with a right-angle edge is helpful
when you are working on flat panels, or when you need to create or
straighten a flange on the edge of a panel.
look at how hammers and dollies are used. Hammers are generally used to
tap high spots down. Whenever you tackle a metalworking project, you
need to have a plan of attack before you start. If you just start
hammering away with no strategy, things are likely to get out of hand!
the crown of a panel, the more strength it has. On medium or high-crown
panels, you can sometimes tap high spots down without using a dolly
underneath. It won’t hurt anything to try this, since either the
hammer will move the metal, or if not it will simply ‘pop back’.
This doesn’t work very well on low-crown (or flat) panels, because
they don’t offer enough resistance, so you’ll probably have to use a
dolly behind the metal on these panels.
So how are a
hammer and dolly used together? There are two fundamentally different
techniques – hammer ‘on-dolly’, and hammer ‘off dolly’. It’s
crucial that you understand the difference between these.
When working on-dolly, the metal being hammered is compressed between the hammer face and the dolly, which makes it microscopically thinner, and therefore ‘stretches’ it. A good way to visualize what’s going on here is to think of the metal as a sheet of pizza dough. As you ‘roll out’ pizza dough with a rolling pin, it gets longer and wider as it gets thinner. This is exactly what hammering on-dolly does to metal. Since the width of the hammered area is increasing, it has to go somewhere, and it will ‘dome up’.
Actually, this is not always the case. The truth is that it will dome more in the direction it is already domed. The vast majority of the time when I hammer on a panel, I’m hammering on a convex surface, and if I hammer on-dolly, the surface will rise. If I am hammering in a ‘cupped’ ‘dipped’ or ‘hollow’ area, the metal will actually go DOWN as I hammer on dolly! Another consideration is that it is crucial to press up on the dolly with a lot of force when you are hammering on-dolly. If you don’t use enough pressure, the process doesn’t work well, and the part you are hammering on may go down instead of up. So in summary, the result you should see if you are hammering on-dolly correctly is that the area you are hitting moves up, while the metal next to the hammered area stays just where it was.
Hammering off-dolly is an entirely different kettle of fish! In this case, the dolly is held so that it touches any low spots on the metal, and you hammer on the nearby high spots. The hammer makes the high spots go down, and the rebounding action of the dolly moves the low spots up! The contact areas of the hammer and dolly have to be pretty close together for this to work– if your dolly is more than about an inch away from the hammer, you probably won’t get much rebound action from it. The hammer may make the high spot go down, but the low spot probably won’t be raised.
And this brings us to the crux of the matter – how do you know where the hammer and dolly are actually touching the metal? Well, let’s start with the hammer. If you are working on clean metal in good lighting, you can often see a small shiny mark left by the hammer blow. If your first blow or two is slightly off-target, you can make a correction on the fly - this is the easy part! What’s far more difficult is to know EXACTLY where the dolly is touching on the back side! With a low-crown dolly, changing its angle even a couple of degrees can make the contact patch move ½” or so! The truth is that it takes a good deal of practice and persistence to learn to control where the dolly touches the metal, but it is exactly this skill that determines your ability to smooth lumpy metal with a hammer and dolly.
beginning metalworkers feel challenged by gaining precise control over
where the dolly touches the metal. Here’s a little trick that can be a
huge help when you’re learning, or when you ‘get lost’. (Hey,
I’ve been doing this work for nearly 40 years, and I still ‘get
lost’ occasionally!) If you can’t tell exactly where the dolly is
touching, hold it still, and tap around with the hammer in a spiral
pattern until you ‘find’ the dolly. How do you know when you’re on
it? By the sound! When you are tapping on unsupported metal, the hammer
blows make a dull ‘thud’ sound. When the dolly is EXACTLY under
where you are hitting, the hammer blow will make a sharp ‘ringing’
sound. Anybody can hear the difference, even when using earplugs! Once
you’ve ‘found’ the dolly contact patch, continue hammering
(lightly) and move BOTH hands together until you’ve brought the
dolly’s contact point to the exact position you want. Then, you can
hammer either on-dolly or off-dolly, as the situation requires.
A great way
to practice these techniques is to get a junk fender, pound some dents
into it, then straighten them. As you build your skill on small, easy
dents, go on to larger, more complicated ones. The simple hammer
on-dolly and off-dolly techniques described here should enable you fix
most damage. There may be times when you can’t get high spots go down
and stay down, and in these cases you may have to use heat to
‘shrink’ the metal, but that’s a story for another time.
each of you to practice using a hammer and dolly until it becomes second
nature. Even if you plan to get an English wheel, Pullmax, Planishing
Hammer, Helve Hammer, or Power Hammer, you still need to learn to master
the simple hand tools, and the knowledge you gain will be a great
benefit to you as you tackle the learning curve of the ‘big tools’.
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