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The Impact of Pad Size on Paint Correction

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The Impact of Pad Size on Paint Correction

A great deal of time is spent discussing the various foam types and face design of pads, but very little attention is paid to the pads diameter and thickness. One could make the case that these factors are just as important as the cutting power of the pad itself. This article will discuss the various aspects of pad size and how that impacts your results when working with a dual action or random orbital polisher.

PAD DIAMETER AND AREA

There are a number of aspects that go into choosing the right pad size for the task at hand. Obviously, the most readily seen is the ‘does it fit?’ principle where you may need a smaller pad to work on more intricate or small spaces, but the diameter also begins to play a role in two other areas.

 A pad with a larger diameter is going to feature a larger polishing area, which carries with it benefits as well as drawbacks. In terms of positives the increased area means you will be addressing a larger amount of the surface, more pad contact means more paint getting polished at once. As we can all likely remember from high school geometry, the area of a circle is calculated as “Pi(R2)” so comparing two common sized pad options below we can see the difference in the area the pad contacts:

Screen Shot 2016-02-16 at 12.46.04 PMAs you can see above, a difference as small as 1″ in diameter actually translates to an overall difference in area of almost 10″. Thats a significant amount of contact area being addressed. This increased contact area, while a benefit in terms of how much surface is addressed at once, has another side effect that actually reduces polishing power.

 As those of us familiar with machine polishing know, in addition to the orbital movement of the pad an amount of rotation is necessary to maximise correction. The increased drag created by the additional area in the example above will cause the rotation of a non-forced-rotation machine to slow or stall with much less pressure. Because some amount of pressure is necessary to achieve correction this creates a situation where the user is constantly attempting to balance between the appropriate pressure and rotation – two forces at odds with each other due to the drag created by the large contact patch.

 PAD DIAMETER AND CIRCUMFERENCE / ROTATION

The other area impacted by diameter of a pad is circumference and in turn rotation. A smaller diameter pad must rotate significantly faster to travel the same distance. This principle can be demonstrated and observed with gears of different sizes in a transmission – the smaller gears much rotate at a much higher rate of speed to keep up with the rotation of an adjoining larger gear.

 When we break down the circumference of the two most common sized pads we can generate a ratio that helps us understand how fast the smaller pad must rotate to equal the same rotation as the larger pad:

 Screen Shot 2016-02-16 at 12.52.55 PM

The ratio of 1:1.18 means that with all other factors being equal, the outer edge of 5.5″ pad will rotate 1.18 times for every rotation of 6.5″ pad. Now while this might not seem like much, but if calculated out over the duration of a paint correction at the high speeds of a machine the implications become more substantial. Again, with all other factors being equal, if a 6.5″ pad is moving at 480rpm on a tool like the Flex 3401, the equivalent 5.5″ pad is rotating at a speed of 566.4rpm an 86.4rpm gain.

 PAD HEIGHT AND MECHANICAL TRANSFER

A factor often overlooked in pad choice is the overall height of the pad and its impact on the machines ability to transfer movement to the surface. Again, just like drivetrain loss in a vehicle where the ‘slack’ in the transmission, flexibility in the drive shaft, and the energy exerted to rotate these components before the power actually reaches the wheels, then the pavement – a polisher has to transfer its orbital movement and rotation thru the spindle, the backing plate, the pad, and into the paints surface. All of these parts have an impact on the translation of that mechanical force, none more than the foam pad.

Borrowing an excellent analogy to represent this concept from an extremely well respected detailer Todd Helme, imagine a 10ft tall pad and you standing on a ladder at the top. If you wiggled that pad at the top in a short orbital stroke the top would move, but by the time that energy reached the bottom it would be completely absorbed and the bottom of the pad wouldn’t move at all. The farther that orbital movement has to pass thru the foam the weaker it becomes until its absorbed completely.

Screen Shot 2016-02-16 at 12.56.30 PM

The same concept applies, at a much smaller scale in thicker vs. thinner pads. The taller the pad, the more energy is absorbed and thats less energy reaching the face of the pads, ultimately weakening your correcting power. On the flip side thinner pads minimise the loss of movement and translate more of the full movement to the face of the pad.

So why not make super thin pads? There are a few reasons – because reducing the thickness of the pad reduces the energy absorbed more vibration will be transferred back to the operator which can lead to discomfort. Also, a thinner pad will be less able to flex over contours or complex surfaces making polishing on anything other than perfectly flat panels more difficult. Lastly theres the issue of durability as a thin pad can tend to deteriorate quickly under the stress and then you risk a backing plate mistakenly cutting through a pad and contacting a painted surface.

On average most pads will range between 0.875″ to 1.5″ thick and even microfibre pads feature a foam backing layer. Because there is a variety and a number of options out there it gives us as detailers the ability to choose a pad that balances our need for correcting power with comfort and utility on complex panels.

 THE IMPACT ON MICROFIBER PADS

Microfibre cutting and polishing pads are a more recent addition to the world of detailing and have already begun to be featured in a variety of configurations. One common thread among all of them is the use of a foam backing. As mentioned above this is to give the pad some flexibility over complex surfaces as well as to absorb some of the vibration from the machine for user comfort.

 Because the intention of microfibre is to cut quickly the preferred pads in this area feature a thinner foam backing. This ensures as much of the polishing power is transferred to the microfiber face and correcting ability is maximised.

 Thicker backed microfibre pads have also shown to delaminate more frequently due to the high friction, heat, and stress placed on the foam backing making thin microfibre pads preferred in most all situations to which they are suited.

 PARTING THOUGHTS

When choosing your pads for paint correction and other machine tasks there is always going to be some level of compromise. Make sure you evaluate your needs and don’t limit yourself with just a few sizes and heights, having a variety of pads at your disposal will give you more options to work with.

 Choose smaller, thin pads when you want to maximise your correcting/polishing power, but realise this means a reduction in the surface you can impact at once and you’ll also deal with an increased amount of vibration from your polisher.

 Select thicker larger OD pads when you don’t need as much correction, but want to speed up the application process by treating more surface at once. In terms of comfort these pads will minimise the feedback vibration you experience as well.

*this article was extracted from adamsforums.com