Porter Cable 7424 XP question

[gioprivatemove]

Hi all,

My XP just arrived a few weeks ago and i got a 6 inch backing plate along with it. I tried it on my car with 3M Polishing pads. I followed every steps and every guides i have read it, but something i don't feel right as i start to polish on speed 5. As i giving a firm pressure on the head of my XP, i see the machine is not spinning correctly (too slow). I lifted my pressure bit by bit, but still no progress, until i just let it go and only the weight of the machine it self then the spinning is good.
Then i compared the results with firm pressure and without. With the firm pressure, i couldn't remove paint minor scratch and swirl. On the other side, just the weight of the machine it self, and i just hold the machine with one hand it totally remove minor scratch and swirl. I am confused...
Is there something wrong with my machine?
Please advice.

Cheers,
Gio

[gioprivatemove]

Re: Porter Cable 7424 XP question

Anyone???

[Michael Stoops]

Re: Porter Cable 7424 XP question

Applying pressure will start to bog down the machine to some degree, that's normal. You generally don't need to have the pad spinning really quickly, but it should still be rotating. Applying too much pressure, or leaning onto the edge of the pad, will stop the rotation - you don't want to do either of those things.

Having said that, your combination of product, pad and even the paint (especially the paint, as a matter of fact) will all play a role in how effective any process is. Some products work best with light pressure, others with heavy pressure. Some paint responds better to light pressure, some to heavy, etc. The important thing is that you've experimented a bit and found a combination that works for you on your car.

We've seen a certain combination work beautifully on one car but not do much to another, or even make matters worse on a third. Nothing is set in stone in this game so experimentation is always part of formulating a plan.

[gioprivatemove]

Re: Porter Cable 7424 XP question

So there's nothing wrong with my machine.

Thank you for your advice. Really appreciate it.

[ai5u]

Re: Porter Cable 7424 XP question

Did you by chance get the 6" counter weight for your PC 7424 XP? Or are you still using the 5" counter weight?

[TOGWT]

Re: Porter Cable 7424 XP question

Perhaps a smaller (4-inch foam) pad will help

Pressure / Pad Compression

Depending on the types of surface abrasions you're dealing with, increase pressure as necessary. Just remember that more pressure equals more aggressive, so be careful around ridges and raised surfaces Maintain the same pressure and work the product in, it may take three or four passes to complete before the residue can be removed. Once you see the desired results move on to the next area, or repeat the process as necessary.

The required pressure applied to obtain optimum results to adequately compress the pad (50%) and obtain uniform abrasion is usually in the range of 10 – 15 lbs. (a random orbital buffer will stall at approximately 20 pounds of applied force)

To compress a 6-inch pad 50% requires you increase the total force by the ratio of its surface areas Ratio = [π (radius2)] / [π (radius2)] = 2.25 as much force, almost 34 pounds).

With the smaller pad you're applying the same force, at a constant speed but over a smaller, more concentrated area, which will induce friction and greater abrasion abilities to the polish, both these abilities require a certain amount of caution as it’s possible to abrasion burn the paint.

[Fly Bye]

Re: Porter Cable 7424 XP question





What you have is an orbital polisher. It moves in tiny orbits because the axis of rotation is offset. The backing plate/pad is allowed to rotate, but is NOT forced. I'll give you an example: Take a black permanant marker and make a dot toward the outside of the backing plate. With a pad that measures anywhere from 5 - 6 1/2 inches, with a nominal amount of downforce, (approximately 5-10 lbs or so max) and the machine set to 4-5, what is that black dot doing???

Get the picture? You'll have to try this to understand what I'm saying. The bottom line is, random orbit polishers do not rotate very much. On the other hand, if you put a 3 3/4 inch backing plate with a 4 inch pad, set the machine to full blast (6 is the max setting on PC) and don't press too terribly hard, what is the black dot doing? It's rotating quite a bit more.

I have a hard time believing that the machine performed more aggressively with just it's own weight versus you applying firm pressure. I have been using the PC for a mere 5-6 years, and that has never been the case.

The firmer you press downward, the less its going to spin. But if you do the black dot test on the backing plate, with the machine set to 4 1/2 and a 5 - 6 1/2 inch pad, the machine is NOT spinning anyway. It's still orbiting!!! That's because it's a "Random Orbit Polisher".

With an adaquate amount of downward firm pressure, the PC will work more aggressive on a painted finished surface than with just the weight of the machine itself. Pressing downward excessively cannot slow the rotation of a PC if it isn't spinning to begin with, but excessive downward force WILL bog the motor.

All it takes to prove this is a sharpie (permanent marker)



Cheers mang

[Fly Bye]

Re: Porter Cable 7424 XP question

Perhaps a smaller (4-inch foam) pad will help

With the smaller pad you're applying the same force, at a constant speed but over a smaller, more concentrated area, which will induce friction and greater abrasion abilities to the polish, both these abilities require a certain amount of caution as it’s possible to abrasion burn the paint.

The 4" pad has less inertia than a 6'' pad, which is why it will spin more in addition to the same downward force being applied to a lesser pad area creating more friction. The fact that the pad is spinning more with the 4'' pad, the setup will create even more friction.

[Michael Stoops]

Re: Porter Cable 7424 XP question

If the pad stops rotating with even light pressure then something isn't right. The counterweight isn't going to make any real difference here, so don't concern yourself with that.

It is very important that the pad be flat against the paint - leaning onto an edge even with moderate pressure can bog the tool down. But you should be able to compress the pad noticeably, especially at speed 5, and still have rotation. Too much pressure will stop the rotation but the oscillation will continue.