4" vs. 6" pad - really more agressive

**abbeysdad** · 10-19-2006, 12:05 PM

I`ve seen a lot of posts that suggest that the 4" pads are more agressive....but I don`t see how.

Assuming the same foam density pad and applied pressure, from the center, the 6" pad is spinning at the same rate at the 4" mark as the 4" pad.

How can either be any more agressive than the other?

**BobD** · 10-19-2006, 12:07 PM

Originally Posted by abbeysdad

I`ve seen a lot of posts that suggest that the 4" pads are more agressive....but I don`t see how.

Assuming the same foam density pad and applied pressure, from the center, the 6" pad is spinning at the same rate at the 4" mark as the 4" pad.

How can either be any more agressive than the other?

The 4" pad will generate much more heat than the 6.5" pad.

**abbeysdad** · 10-19-2006, 12:14 PM

I guess I don`t see how since it will spin at the same speed and see the same surface resistance (at the 4" from center mark). How does it generate more heat?

It would seem that to generate more heat it would need to spin faster or see greater resistance/friction.

**AL-53** · 10-19-2006, 12:23 PM

with a 4" pad you have less surface resistance...and the 4" pad really works fast.. does more spin like motions than the jiggle......you will get some HEAT also..I played around on a test panel and I was polishing near a edge and seen smoke come out...so it does heat up...

you will do corrections much faster..be you need to be careful....you can burn paint...I tried and did....

I have both a rotary and a PC..and when it comes to just do a spot correction..I use the 4"..

I think the 4" is a very good system...just need to be careful...speed 5 is tops for me..6 is very radical..lol....really cuts...

need a good backing plate..and I got mine from Patrick at excel and pads also..and they are very good quality....some here have melted thier 4" BP...believe it was called a spot buff BP..but patricks is made like a tank....3M also sells one that is very good.....

AL

**Accumulator** · 10-19-2006, 12:31 PM

A few thoughts: with the smaller pad you`re applying the same force but over a smaller, more concentrated area. Also, and IMO this is the key with regard to the PC, the lighter weight means that the machine doesn`t bog down and just "jiggle" the way it will with a larger pad, especially under applied pressure. The smaller pad`s lighter weight is more like the weight of a backing plate with a single sheet of sanpaper stuck to it (which is all the PC is really designed to use) so you get both of the "dual action" motions- IMO more motion = more work being done.

The damage I did to the MPV`s clear with a 4" pad would`ve been simply impossible to do with a larger one. It looked exactly like a rotary burn, only time I`ve ever seen (let alone *done*) such damage with a PC.

**fdizzle** · 10-19-2006, 12:46 PM

props to accumulator . . .

so can the spot buff kit that autogeek sells, which i have, be used for this 4`` application, it did come with an adaptor for the PC and a drill . . .

**AL-53** · 10-19-2006, 01:03 PM

I am glad Accumulator jumped in..lol...I was trying to compose my thoughts..and he did a good job telling why the 4" pads work so good...what my brain says and what my fingers type are so different..age I guess...

fdizzle..careful..those were one of the BP`s that were failing awhile back....it had to do with the screw in adapters ..one for the PC and one for the drill.....Mikeyc had problems with his..and a few others..it sorta unscrewed when using and scratched the paint....some melted....

Al

**the other pc** · 10-19-2006, 03:32 PM

Assuming equal orbital speed, orbital radius and foam compression the difference between 4" and 6" pads is their surface area and therefore surface friction. The 4" and 6" pad should have identical aggressiveness per unit area with the 6" pad having the greater overall material removal rate due to its greater surface area.

In the real world the increased friction of the larger pad bogs down the PC and reduces application speed and perhaps the orbital radius as well. Weight may play a role but surface friction surely dominates the effect. The 4" pads are easier to keep driving hard.

It`s the opposite with the rotary. Orbitals have constant cutting radius over the surface of the pad while a rotary has a cutting radius that varies from zero at the center, increasing out to the edge. So larger pads on a rotary have greater cutting unless the machine is so totally wimpy that it practically stalls out with a larger pad.

I would be very curious to see how orbital radius at the pad/finish interface relates back to pad size, foam compression and drive orbital radius. I would strongly suspect that it`s neither constant nor linear.

PC.

**Accumulator** · 10-19-2006, 05:15 PM

the other PC- Interesting...perhaps I`m utterly off-base regarding the weight being an issue, I coulda been letting the tail wag the dog here. I suppose it *could* be the additional friction from the larger surface area that makes the PC merely "jiggle" which simply doesn`t happen, *in my experience* with the smaller pads. Hmm..I simply don`t know so I`m open to your explanation being correct :nixweiss It certainly *sounds* sensible, to the point of "gee, how`d I miss *that*".

You`re saying that the smaller pads *don`t* result in a greater amount of work being done because of a concentration of force over a smaller area, right? Sheesh, I wish I could remember more from my school days

**the other pc** · 10-19-2006, 06:24 PM

I`m not saying weight isn`t a factor (that`s why I said I`d be curious how the different factors play together) it`s just that the act of buffing is by definition a process of friction. (There are non-friction polishing techniques for some materials, flame, chemical, etc but buffing=friction.)

The 4" pads result in a greater amount of work per unit area, in other words they cut deeper but over a smaller surface area. The 6" pads could cut that deep if they could be driven as hard. But a PC just doesn`t have the power to do it.

Let`s say that to get maximum cutting efficiency with a given foam formula you have to compress that foam by 50% and for a 4" pad that takes 15 pounds of force. To compress a 6" pad that same amount requires you increase the total force by the ratio of their surface areas = [pi*(6/2)^2]/[pi*(4/2)^2]= 2.25 times as much force, almost 34 pounds. But a PC usually bogs down around 20 pounds so you can`t get close to the maximum cutting capability of the foam.

If you had a 5hp PC you`d be able to keep it going, no problem.

The reason you`ve never seen 4" pads "jiggle" is because you`ve never leaned into them so hard that it bogged down the machine. It can be done but it`s abusive and unproductive.

PC.

**BaseSteala112** · 10-19-2006, 10:56 PM

Originally Posted by Accumulator

A few thoughts: with the smaller pad you`re applying the same force but over a smaller, more concentrated area.

:werd:

Thhink of it as getting your foot stepped on by a regular shoe and getting it stepped on by a stiletto. Much more force exerted over a smaller area.

**the other pc** · 10-19-2006, 11:25 PM

ItÃ¢â‚¬â„¢s only more concentrated if you have the same force on both.

If you have the weight of an anorexic supermodel on the stiletto verses balancing a Mack truck on the regular shoe the end result is different.

PC.

**LeadingEdgeDetail** · 10-20-2006, 01:13 AM

Wow, should be common sense, no?

A 4" pad will have 12.56sqin of surface area, whereas a 6" pad has 28.26 square inches.

If you apply 10lbs of force for each, that`ll be 0.8lbs per sq-in, versus 0.35 for the 6" pad. Pressure = Friction = Heat = Better cutting ability!

And this isn`t even considering how much better the PC operates with a 4" pad over a 6! :getdown

**BaseSteala112** · 10-20-2006, 10:05 AM

Originally Posted by the other pc

ItÃ¢â‚¬â„¢s only more concentrated if you have the same force on both.

If you have the weight of an anorexic supermodel on the stiletto verses balancing a Mack truck on the regular shoe the end result is different.

PC.

I thought that would be a given. Just becuase you are using a smaller pad doesn`t mean you have to exert more or less force. I assumed he would not change the amount of force applied, just the pad size.

And as for the example you used, I get it, it`s just too general. Less force over a smaller area (anerorexic supermodel + stiletto) will be quite similar to a greater force over a larger area (mack truck + regualr shoe).

**BaseSteala112** · 10-20-2006, 10:08 AM

Originally Posted by StumpyDetailing

Wow, should be common sense, no?

A 4" pad will have 12.56sqin of surface area, whereas a 6" pad has 28.26 square inches.

If you apply 10lbs of force for each, that`ll be 0.8lbs per sq-in, versus 0.35 for the 6" pad. Pressure = Friction = Heat = Better cutting ability!

And this isn`t even considering how much better the PC operates with a 4" pad over a 6! :getdown

:werd: It`s all physics.