What can paintless dent removal do?
Paintless dent removal is really best on small dents no larger than a 50p, it can be used on dents that are larger but the results can be mixed! - it all depends on things like the thickness of the bodywork and the position of the dent. (PDR needs to be done on metal body panels - See Bumper Dent Repair)
The problem is that you can never get dents perfect... they just look perfect! Here is what happens when a panel gets dented.
If you look carefully you can see that the panel has become stretched. The shortest distance between point 'A' and point 'B' is a straight line, so the fact that the metal is now in a curve means that it HAS to be longer than the area you want to push it back into. The extra length has to go somewhere because unfortunately, you cannot shrink it back.
So what happens is that when you push it back you actually get a ripple in the metal - this is shown in the diagram above. Both these diagrams are heavily exaggerated and on the real thing you wouldn't notice the ripple because it would be too slight and would be hidden by the ripple that is on the cars paintwork commonly known as orange peel.
(It isn't usually as pronounced as in this picture but that is because this is a poor quality respray).
The larger the dent is, the more the panel can get stretched - so the less likely it is that the dent can be totally removed - we can usually make an improvement, but this will also depend on conditions. We do say on our dent pages that we can only remove a dent if it doesn't cross a swage line, if the dent doesn't form a crease, and if the paintwork is un broken... this leads to many people sending us dents that meet this criteria, but are too severe for us to do, or we can only make an improvement on. If we can make an improvement, we need to make a judgment as to how much of an improvement we can make which is a matter of experience, and make a judgment as to 'an improvement' will suite the car - obviously an improvement isn't good enough on the bonnet of a 2 year old Mercedes, but it may be good enough if it is a 7 year old Ford and the dent is some place less obvious such as below knee height.
The Size of Dents
As you can see, the larger the dent, the more difficult they are to do and the more time needs to be spent on them. So we price dents accordingly and to give a rule of thumb we describe dents on our gallery as being 50p size, plum size, orange sized of football size. However, dents are not always the size they first appear to be. Our prices are are based on the visual size which is usually the outer ring of the high point.
Figure 1. shows how dents can effect a curved panel such as a shoulder on the top of a wing. Because the rim of a dent tries to level it's self out, as the centre of the panel is pushed in (large blue arrow Fig.1b), some areas are pushed outwards. Fig.1c shows how the panel is distorted to an area which can be roughly double the size of the dent which is obviously visible.
The good news is that in many cases, as the dent is pushed outwards, the distortion of the panel can return to it's natural shape on it's own, but not always.
Figure 2 shows how a dent can be larger than it first appears if a sustained pressure is applied, the impact area results in an obvious indentation, but a larger area is actually dented. Sometimes on larger dents, the panel appears as is shown in fig.2b resulting in a sharp dent within a shallow dent. Sometimes the panel springs back leaving a ridge as shown in fig.2c.
The outer area of the dent can actually be obvious (i.e. a visual size), but often people don't see it because they are focused on the even-more-obvious indentation in the middle.
Some dents that are more difficult
than you may think...
Quite often, dents that look small and easy to do are not possible at all because they are in places where we cannot get to them from behind.
In figure 3, the red rod represents a dent removal tool. As the dent is pushed from behind, it can push the return edge of the panel outward which acts like a spring. Dents on these kinds of areas can be difficult to do, but not impossible, it often depends on the severity of the dent.
Figure 4a shows a cross section of the edge of a door and door frame (door 'L'). The seam on the door is usually triple thickness making it very resistant to denting, but if you did get a dent directly on it it would be virtually impossible to remove. It's quite common for dents to appear right next to this seam, and because a dent is removed by starting from the outer edge and working inward, it can be very difficult to remove because the seam shields the very outer edge Fig.4b.
Figure 4 also shows how a dent on an edge can be more serious than it first seems because a panel will fold easily at a point where it is already folded.
Figure 5a - This is fairly typical of a double-skinned area, often found on rear wheel arches and rear quarter panels. Often these sections are completely enclosed making access from behind impossible.
Figure 5b - Is a good approximation of many roof edges, consisting of a 'box-section' and a main centre panel. The box section is often totally enclosed, however, more recently there are access holes allowing for the fitting of air-bags... but this doesn't always help if the airbags are in the way.
Figure 5c - This is typical of a frame found under large panels such as bonnets. Usually these frames are not totally enclosed and have holes in them which allow partial access.
Figure 5d - shows a cross section of a door. In recent years it has become more common to build extra strength into the door by combining side impact bars as part of the design. As a result, doors can contain box-sections and double skins... but not always.
Not all box sections and double skins are completely enclosed, some have holes in places for things like wiring to pass through, or just cut to save weight. And if there are no ready made holes, it is possible to make small holes for the purpose of access if they fall into very discreet areas. This is done with a punch which unlike drilling, will not leave metal swarf which can lead to corrosion. Afterwards the hole is sealed and filled with a grommet.