If I had to name a single product
that has caused the most excitement and confusion among car appearance
enthusiasts in the past ten years, it would have to be the Porter Cable
7424 Random-Orbit 6" Polisher. Its name alone is a huge source of
confusion, as it goes by several different nomenclatures, including
"PC" (Porter Cable), "DA polisher" (dual-action polisher),
"ROB" (random orbit buffer), or any of its model variants, including
7334, 7335 or 7336. If you're interested in knowing more about any of
these models, visit www.porter-cable.com.
The Porter Cable (PC) 7424 started life more than a decade ago as a sander
for woodworkers. Much like custom car builders, fine furniture artisans
sculpt a piece of furniture, stain it to a desired color, then spray it
with multiple coats of clear polyurethane. To achieve the final finish,
they wet sand, compound, polish and wax.
system contains the machine, a single foam pad, wrench and
very brief operating instructions.
With the introduction of foam buffing
pads into the woodworker industry in the early 1990's, it's not hard
to see how the PC 7424 came into use on car finishes. Clearly, this is a
hobbyist and detailer movement, as Porter Cable did not design and does
not market their 7424 for use on automobile finishes. So, why is the PC
7424 so popular within the car enthusiast hobby? Let's explore the inner
workings of the machine.
The term random orbit defines the action of the tool's
head. Unlike a rotary buffer, that spins at variable speed on a
stationary spindle, a random orbit machine operates by spinning the head
(free-spinning) on a center spindle and running this spindle around an
eccentric offset. I measured the net pad throw (side-to-side) at a
generous 15/16 inch.
Here's a great example of what the PC 7424 can do
when used with a good polish and pad. Autopia member ZaneO
use an Orange cutting pad with Menzerna Intensive polish followed
by Menzerna Finishing Polish and a fine foam pad. As
you can see, even a badly oxidized finish can be restored.
Some people have defined the PC
7424's tool action as "jiggling", but this is not the case. The head
freely rotates on a bearing and orbits around the centerline driveshaft.
Rotation is a free-wheeling action of the backing plate spindle caused by
the orbiting head. This "dual-action" is where the PC 7424 gets its
The fact that the backing plate spindle is free-spinning is what allows
Porter Cable to call their 7424 a random orbit machine. In practical
terms, there's nothing random about the polishing action. At about one
pound of constant, even pad pressure, the backing plate spindle of the
7424 stops spinning.
The PC 7424 most closely mimics circular hand polishing. Imagine being
able to make 2,500 to 6,000 tight hand circles in a single minute and
you'll have a pretty good idea of how the PC 7424 does its job. It works
just like your hand, only at Superman speed! To put the beauty of this
machine into complete perspective, it works 100 times faster than a buff
athlete, but it never gets tired!
system from Sonus has three grades of 7" foam pads and
5" flexible backing plate. The Velcro backing is
recessed into the pad, offering complete protection from potential
backing plate mishaps.
As long as I'm comparing the PC
7424 to an athlete, I should mention that it's also adept at more than
one game. Given the appropriate athletic gear, the 7424 is a tri-athlete,
excelling at polishing, waxing and buffing. With the proper brush
attachments, it has also been known to tackle carpets and upholstery.
If you have previously owned a random-orbit car polisher that made a lot
of racket, but did little else for your car's finish, you will
appreciate why I call the PC 7424 an athlete. Most consumer "car
polishers" don't have enough power, have a very small orbit (often
less than 1/4 inch), and have limited accessories. The PC 7424 is the
first machine to shatter these limitations.
BASIC FEATURES & OPERATION
The PC 7424 has a powerful motor for its size, yet it pulls a scant 3.7
amps at 110 volts. If you don't have a garage, you can run the PC 7424
off of your car battery using a 750+ watt power inverter. The tool uses a
standard 5/16-24 spindle, so a lot of different attachments will fit.
In pictures, the PC 7424 looks larger that it is. It measures about 10
inches in length and weighs a tad less than 6 pounds with a backing plate
and pad attached. A reversible side handle makes the PC 7424 very easy to
hold and control, even when working on vertical surfaces. Use of the side
handle is a personal preference. It adds a bit of safety, but people with
large hands may find it just as easy to grip the machine by the head with
a single hand.
The machine functions at 2,500 to 6,000 operations per minutes (OPM),
controllable by a thumbwheel on the rear end of the machine. The OPM
measurement is used instead of revolutions per minute (RPM) to distinguish
the difference between orbits and center shaft revolutions. At 6,000 OPM,
this machine is doing a lot of work.
The standard PC 7424 comes equipped with a single white foam polishing pad
that is permanently fixed to a 5" baking plate (Porter Cable calls them
back-up pads). The standard foam pad is great for general purpose
polishing and waxing. Due to the replacement cost of Porter Cable's foam
pad (p/n 54745), most PC 7424 owners quickly switch to a Velcro backing
plate and Velcro backed foam pads.
Changing pads and backing plates is easy. You use the flat spindle wrench
supplied with the machine to hold the spindle and rotate the backing plate
counter-clockwise to loosen or clockwise to tighten. When tightening, it
is not necessary to turn the backing plate more than 1/4 turn once it has
initially seated. Do not over-tighten. Snug is just fine.
Changing backing plates is easy. Use the
flat wrench provided with the PC 7424 to hold the center spindle
and unscrew the backing plate with your hand. Do not
For safety reasons, Porter Cable
recommends that the machine not be operated unless the pad is flat on the
work surface. That means you both start and stop the machine while it is
resting flat on the surface of the car. If you're not going to follow
this safety precaution, please wear safety glasses.
To operate the machine, follow these simple instructions:
Your car must be freshly washed
and dry. Do not buff on a dirty finish.
Work in an area with good
lighting. Overhead fluorescent or halogen lighting is best.
Remove all rings, watches,
bracelets, belts and other items that will scratch your paint.
Wear an apron to protect your
clothing and the paint finish.
Adjust the machine speed to 3 or
4 on the thumbwheel. This is a good starting point.
With the machine switched off,
apply a small amount of polish, cleaner or wax directly to the
polishing pad. There are two good methods that seem to work. Squeeze
out a complete ring of product about 1 inch in from the outside of the
pad, or squeeze out an "X" of product across the pad.
Dab the pad in 3-4 spots around
the area to be polished, cleaned or waxed to distribute the product.
Position the polisher flat on the
work surface, get a firm grip and switch it on with your thumb.
Move the polisher back and forth
(east/west) in a slow, sweeping motion, overlapping each pass (by 50%
of the pad width) with the previous, and then switch your pattern to
up and down (north/south).
It is not necessary to apply more
than a pound of pad pressure. Allow the polisher to work under its own
Use a clean pad with each
product. Do not mix products on a pad. If a pad is not dirty, you may
store it in a Ziploc baggie for future use. Be sure to label the
baggie or the pad.
If a pad becomes caked with
product, use a nylon or horsehair detailing brush to clean the pad.
Sounds pretty simple, doesn't it?
It really isn't difficult. Within a few minutes of use, most people are
very comfortable operating the machine.
BUFFING PADS & BACKING PLATES
It's possible to use a range of backing plates and pads with the Porter
Cable 7424. Velcro backing plates are available in sizes ranging from 3 to
For proper and safe operation, the backing plate and pad combination must
be balanced to the installed counterweight. The purpose of the
counterweight is to dampen harmonic distortions (vibration) caused by the
pad whipping around in its tight orbit. If the counterweight was not in
place, you would not be able to hang on to the machine for more than a few
minutes before your hand went numb.
backing plates come in a wide range of sizes. For
safety, be sure to use a backing plate that is slightly small than
In general, the 5-inch counterweight
(p/n 874011) should be used with a 5-inch or smaller backing plate,
whereas the 6-inch counterweight (p/n 699933) must be used with a backing
plate larger than 5 inches. Weight is the true determining factor for the
proper counterweight, not the backing plate or pad size. If your machine
vibrates excessively, you may need to switch counter weights. You will
need a Torx driver (size T15, not supplied with the machine) to swap
While on the subject of weight and counterweight, the lighter the backing
plate and pad combination the more efficient the machine will be. Some
suppliers assemble backing plate and pad combinations that have no
business being connected to the PC 7424. After several years experimenting
with a variety of backing plate and pad combinations, I have concluded
that a light weight, 5-inch, flexible backing plate used in conjunction
with a 6- to 7-inch pad achieves the best results. Larger backing plates
and pads apply too much torque on the motor and rob efficiency. Also, to
improve safety (stuff happens!), it's best to use a pad that offers .75
inch or more foam clearance beyond the backing plate.
There is an almost dizzying selection of pads that can be attached to the
PC 7424. Here's a quick run down on categories:
"Tufted" Finger Pads
Contour/Variable Contact Pads
Advanced foam pads, including
different variations of the waffle, tufted and variable contact pads were
designed for use on high speed rotary buffers. I find some benefit in
using contour pads for heavy repair work (cutting pad), but not enough to
call them a significant advantage over flat pads.
Within each of these categories, you will find several grades of pad from
coarse (heavy cutting pad) to very fine (waxing and final finishing pad),
and sizes ranging from 3 to 9 inches.
There's an amazing selection of foam
pads for the PC 7424. I find that flat pads between 6-
and 7-inches work the best.
The effective pad contact diameter
for the PC 4724 is 5.5 to 6.5 inches. Pads must be matched to an
appropriate polish to achieve the desired results. Don't try to use a
fine hand polish with a cutting pad to remove heavy oxidation or swirl
marks. It simply won't work.
I find that using a 5-inch flexible backing plate with 6- or 7-inch flat
pads offers the best results. I discourage the use of coarse "cutting"
pads (normally yellow) by inexperienced users due to the real potential of
removing too much paint material or creating hazing in the paint.
SELECTING THE RIGHT POLISH
Most of the major polish manufacturers make a selection of abrasive
papers, compounds, cleaners, polishes and glazes to meet varying polishing
requirements. Here's a quick definition of polishing abrasives:
Abrasive paper or pad - An ultra-fine grade of sandpaper (1500 to
3000 grit) that can be used effectively to level a paint finish and remove
imperfections. I mention sandpaper here because it is an abrasive, like
all polishes, and it has its place in the polishing process.
Compound - A compound, often called a rubbing compound or a paint
cleaning compound, is a cutting polish designed to remove heavy oxidation,
some common forms of paint damage and defects, and the scratches created
by fine sandpaper. Use compounds with a foam cutting pad. Always start
with the least aggressive pad and compound possible.
Polish - A specially formulated blend of components designed to
remove minor scratches, surface imperfections, water spots, acid rain
spots, light oxidation, and the swirl marks created by compounding with a
machine. Use a foam polishing pad or a fine cutting pad.
Glaze - A very fine polish. Some glazes are safe to use on fresh
paint, as they do not seal or contain silicones. A glaze does not have
enough cutting power (if any) to remove imperfections, but will increase
surface gloss. Use a fine foam polishing pad or a finishing pad.
Pre-wax cleaner - A fine polish containing chemical cleaners to
help remove minor surface contamination and dirt not handled by normal
washing or claying. Use a fine foam polishing pad or a finishing pad.
Each of these levels of polish can be used with a PC 7424, however, only a
professional or very experienced user should undertake using the PC 7424
with abrasive papers or pads. Always follow the manufacturer's
directions. Do not use a polish that is not specified by the manufacture
(or a qualified source) for use with a dual-action machine.
A few of the larger polish manufacturers, who make paint polishes that
work with dual-action systems, include: Meguiar's, 3M and Mothers.
There are dozens of polish manufacturers, so I won't attempt to mention
MAINTAINING & IMPROVING PAINT
It is polishing, not waxing, that offers the most improvement in the
overall appearance of paint. If you wax over bad paint, it's still bad
paint. When you polish bad paint (paint with scratches, heavy oxidation,
swirl marks, stains, water spots, etc.), you remove the bad paint to
reveal a fresh finish. Obviously you can only do so much polishing before
you wear out (thin or completely remove) the paint, so only polish as much
as necessary to maintain healthy paint.
Buffing pad and polish makers create products with different levels of
aggressiveness to make your polishing tasks faster and easier. You can use
an aggressive pad and polish combination to quickly remove paint defects
or severe oxidation, but it won't reveal the full gloss potential of
your paint finish. Just like polishing a jewel, you must use several
grades of polish to bring out the final radiance.
If your paint is new or like new, it is not necessary to use heavy
abrasives. You can use very mild pre-wax cleaners and glazes to maintain
the factory finish or create a finish that glows like a gem. To do so, use
a fine polish and a foam polishing pad, and work the polish in with a
light touch until most of the polish residue is gone. Remove the remaining
polish residue with a quality buffing towel. Fine polishes won't take a
lot of heat before they cake up and clog your pad, so don't apply
pressure to the machine. Allow the pad and polish to do the work.
Some polishes respond well to a microfiber buffing bonnet, while others do
not. If you're using a polish that is not buffing out clear, try doing
the final buff out with a microfiber bonnet over a clean pad.
Here's how I use my PC 7424 to keep
my paint looking new:
1: Apply Polish To Pad
Select a good pre-wax cleaner or cleaner/wax.
I like Sonus
Paintwork Cleanser. Klasse
All-In-One (use on new and like-new paint) and Autoglym
Super Resin Polish (use on older, oxidized and scratched
paint) also work well by machine.
2: Distribute Polish On Work Area
Distribute the polish over the work area.
If you don't, the polish will sling off of the pad. You can
dab it, as I have done here, or smear it.
3: Start Polish At Low Speed
Start the polisher at a low speed (2 or so on the
dial). Get the polish loaded into the pad before increasing
4: Increase Speed and Work-in Polish
Work the polish into the paint. Keep the
polisher flat, and apply just enough pressure to keep the buffer
in contact. Use slow, smooth back-and-forth and up-and-down
sweeping motions. No need to be getting "jiggy"
5: Polish Until Film Is Nearly Gone
As you work the polish, the film will get lighter
until only a slight haze remains. At this point you can stop
and inspect your work. You can remove the remaining polish
haze with a buffing towel or switch to a finishing pad.
6: Switch To A Finishing Pad or Bonnet
You can use a finishing pad or a bonnet to remove
the final polish residue. Some people prefer doing this step
7: Remove Dust With A Detailing Spray & Buffing Towel
The polishing pads will leave dry dust on the
surface. Use a detailing
spray and a soft buffing towel to wipe away the polish dust
Switch To A Finishing Pad For Waxing
After polishing, use a finishing pad to apply
your favorite wax.&nb
After waxing, use a horsehair
detailing brush to remove polish and wax residue from all
cracks and crevices.
10: Inspect Final Finish
After polishing and waxing, your final paint
finish should be smooth, glossy and wet looking.
REMOVING COMMON PAINT
If you allow the paint finish to degrade from oxidation, water spotting,
acid rain damage and other environmental hazards, you will need to remove
the damaged paint to restore the finish. Even if you meticulously care for
your car, sooner or later we all get paint defects. Polishing removes a
very thin layer of damaged paint to reveal fresh paint and a restored
The PC 7424 is an effective tool for removing most paint defects,
including surface scratches, swirl marks, sanding marks, water spots,
chemical etching, oxidation, scuffs and paint transfer. All of these
problems are addressed in essentially the same way.
You start by using a cutting pad in conjunction with a fine rubbing
compound to remove just enough paint material to cut away the
imperfection. I have always found that removing about 90% of the
imperfection in this step is plenty. Leave a bit for the final buff out,
or you'll remove more paint than necessary.
After compounding, you switch to a polishing pad and a gloss enhancing
polish (often called a "swirl remover polish") to remove the hazing or
light dulling caused by the compound. This step will remove the remaining
10% of the imperfection, and reveal smooth, healthy paint.
Be very careful compounding and polishing on heavily oxidized paint until
you know how much healthy paint is remaining. You could find yourself
removing too much paint, creating thin spots or worse. If you over-buff an
area of paint, you will completely wear away the clearcoat or color. The
only repair for this mistake is to have the panel repainted.
You may find that you have to polish an area several times, and with a
couple different polishes to get results. Don't get discouraged, this is
not uncommon. Slow progress is better than rapid progress when it comes to
If you have a small area with deep damage that the PC 7424 cannot remove,
you have a couple of choices: you can polish by hand using a heavy rubbing
compound, you can wet sand with 1500 to 2000 grit paper, you can switch to
a rotary buffer and a cutting polish, or you can live with the improvement
Machine polishing is messy. No matter how skilled you become, the machine
will always sling off polish. To avoid a huge clean up job, I recommend
using an old bed sheet to cover areas of your car that you don't want
splattered with polish. This little step will save you a lot of clean up
Polishing can be quite detrimental to trim. If you need to polish close to
trim, I recommend masking it with painter's masking tape. If you run
your polisher against black plastic trim, rubber seals or brushed aluminum
trim, you run the risk of ruining the original matte finish. Masking
around window trim, door handles, windshield washer nozzles, antenna
masts, door guards and other trim will reduce your clean up work and save
you a lot of heartache from mistakes. Be safe; take the time to mask off
Use masking tape to mask off trim
around windows and areas where polishing would harm the finish.
It only takes a few minutes to do an entire car. In the end
it will save you a lot of time and grief.
Many people mistakenly believe that polish should be used sparingly. Doing
so puts more of the workload on the pad and causes the polish to dry out
before you achieve any work. Use polish liberally. Apply enough polish to
work an area for one to two minutes before the polish hazes and begins to
Polish safely by keeping the pad flat on the surface you're buffing and
the cord off of the paint. I like wrapping the cord around my wrist once
and draping the rest over my shoulder. You'll have to find a solution
that works for you.
Polish with the pad flat on the surface. If you tilt the polisher, you
risk excessive heat build-up, pad destruction, and potential damage to
trim. Unlike a rotary buffer, which is capable of applying energy to the
edge of the buffing pad by tilting the buffer a few degrees, a dual-action
polisher is not able to effectively focus polishing action. Tilting your
PC 7424 will quickly destroy foam pads (it causes the backing plate to cut
into the pad) and may build-up enough heat with a rubbing compound and
cutting pad to burn paint.
I like to prime a fresh, clean pad with a shot or
two of detailing spray. Doing so makes the initial buffing a little
smoother. Use just a light mist. Don't drench the pad.PAD & PC MAINTENANCE
When your pad becomes caked with polish, use a small nylon or horsehair
detailing brush to gently remove the polish. This must be done with the
polisher switched off. I like the horsehair brushes the best, as they
don't seem to rough-up the pads as much.
A dual-action polisher and a rotary buffer work polishes very differently.
Using a rotary buffer to compound a car, you would run the buffer at a
speed range from 500 to 800 RPM. The size of the pad, the torque of the
motor, and a little pad pressure generate the right amount of heat to cut,
break down the polish and bring up paint gloss. With a dual-action
polisher, pad speed generates the energy necessary to get results from the
polish. So, you have to turn the speed up on the PC 7424 to remove
The PC 7424 is a low maintenance machine. Porter Cable recommends yearly
lubrication by a qualified repair center. If you use the machine
professionally, I would follow the manufacturer's recommendation. For
the typical enthusiast, sending the machine in for lubrication every three
of four years should be sufficient.
There are varying opinions on pad cleaning techniques. Not long ago, the
pad manufacturers themselves would tell you not to wash the pads, as the
water and detergent would de-laminate the Velcro from the foam. For the
most part, this seems to be resolved.
If you are a professional detailer, washing pads after each use would be
very time consuming. The best solution for the professional is to keep
pads brushed clean and store them in large Zip-lock baggies. Mark the back
of each pad with a marker to indicate which product is on the pad. When
the pad becomes too dirty to use, wash it.
Use a detailer's brush to brush dry and caked-on
polish off of your pads. You can use a nylon or a horsehair
brush. I prefer the horsehair, as it does not rough-up the
Do not wash pads in the washing
machine. They must be hand washed. To do so, simply add an ounce of dish
washing detergent to a 5 gallon bucket and fit it with water. Soak the
dirty pad for up to 30 minutes. After soaking, massage the pads to work
out the caked in polish, then squeeze out the soapy water. Empty and
refill the bucket with fresh water. Rinse the pads in the bucket of fresh
water, squeeze, and set aside to air dry. Do not machine dry.
Soak your pads in a bucket of water and add a pad
cleaning solution. Sonus
Der Wunder Wasche is designed specifically for cleaning
microfiber towels and foam buffing pads. It's a low foaming
detergent that's easy to rinse. Allow pads to soak for up to
PRACTICE MAKES PERFECT
While the PC 7424 is a very easy polisher to master, practicing on an
older car with an imperfect finish is the best way to learn. You should
experiment with a variety of polish and pad combinations until you learn
how to achieve the best results.
There is no silver bullet combination of pads and polish. How you use the
machine, your climate, paint hardness, paint color and other issues will
all factor into the final results. Don't get frustrated if your initial
experience is not perfect, as the smallest change (a different pad, polish
or speed) can make a huge difference.
Here are a few before and after pictures of vehicles with severe paint
damage that were restored using a Porter Cable 7424.
Member Deemo: Ford F150
The finish on this Ford F150 has cobwebs,
scratches, heavy oxidation. Deemo used Meguiar's Dual-Action
Cleaner/Polish with a Lake Country cutting pad to remove the heavy
damage and finished with Meguiar's #9 Swirl Mark Remover and a
The paint finish buffed out to a near mirror-like
shine. Full gloss is back and all cobwebs and minor
scratches are gone.
Autopia member Jngrbrdman tackles this Dodge
Neon for a friend. The swirls marks in the clearcoat were
removed using a Meguiar's foam cutting pad and Meguiar's
Member TortoiseAWD: Ford F150
This Ford F150 was a swirl mark poster child.
TortoiseAWD used a foam cutting pad and 3M Fineness-It II polish
to remove the swirl marks and bring the hazy, oxidized finish back
The smile on the face of the owner (right) tells
the final story. Wow! What a difference.
Autopia member Mosca use an Orange cutting and a
tufted finger pad with Meguiar's #83 Dual-Action Cleaner/Polish to
remove the swirls from this Audi A4's finish. Mosca
restored full gloss with a foam polish pad and Menzerna Final