about rotation

**Todd@RUPES** · 04-23-2011, 05:31 PM

Originally Posted by glfahlc

i recently purchased a 7424xp and used a couple of times. previously being a rotary user i noticed with little pressure the xp stops rotating. is it important to the ability to correct or does it not matter that the pad doesn`t rotate. the only way i get positive rotation is if i turn all the way up to speed six. i want to correct with the xp and polish with the rotary.

What size pads are you using? What size backing plate are you using?

The rotation of a PC is driven by the orbital speed. The faster the machine orbits, the more centrigual force is applied to the backing plate (which in makes the pad want to spin). One of the draw backs of foam pads on a DA is that they have a tendicancy to absorb the orbital action of the pad (like a sponge).

Because of this reason using low diameter 5.5 inch pads will really wake the PC up.

Originally Posted by 93fox

I think you should do it the other way around, correct with the rotary and polish with the pc IF you are not getting the results you want with the rotary. one other thing, the pc is pretty useless if you are not using it with 5.5inch pads. Any pad bigger than that will bog down and wont spin, and if it dosent spin, you arent doing any correction. Grab a sharpee and mark a line across the backing plate, if u see the line spining it means you are doing good and getting work done, if not, you arent doing much. But like i said, 5.5 pads are key to the pc. Bigger pads with VERY little pressure will stop rotating. Its why i am looking to sell my pc and buy me a Griots Garage DA.... that thing is impossible to make it stop spining.

Just food for thought...

The power of the machine has *nothing* to do with the pad`s spinning rate (RPM). The reason I *`d nothing is because it obviously has something to do with it, but the effect is very indirect.

What makes the pad spin is the size (stroke) and speed of the orbit. Think of the orbit like a bicycle pedal. The distance from the pedal to the axle would be considered 1/2 the stroke. Since the pedal orbits the axle on both sides, we add the distance together to get the stroke.

And this is why power rating of a machine is slightly misleading. Regardless if a machine has 1 horsepower or 5000 horsepower, if it is able to maintain full OPM (orbital speed) under pressure then it will spin the pad the same rate, regardless of pressure. Granted the 1 horsepower machine will likely be working much harder to achieve that speed (more % of its potential).

The power of a machine can potentially resist how much the speed decreases when friction is applied to the orbital motion. I don`t care how hard you press down on a 5000 horsepower DA, you aren`t going to bog it! But here is the catch, the orbital action (5/16th stroke) is fairly efficient and even under pressure it is hard to slow the orbital motion down. Most of the friction (that stops the pad from spinning) is taken up in the bearing of machine. The only real force acting to bog or slow the orbital speed is the internal flex inside the pad. A firm, thin pad is going to transfer more of that friction (from the paint) directly to the orbital motion where as a oversized squishy foam pad is going to jiggle on itself and absorb the friction. It gets a little confusing (which is why pad dynamics play such a HUGE role in DA polishing) but a big, tall foam pad will stall the spinning easier (since their is more friction at the paint`s surface) but most of that friction will be absorbed by the foam, which can make it harder to stall the orbital motion.

Most modern DA`s are rated at 6800 OPM maximum and most (because of pad dynamics) will maintain that orbital speed under significant pressure, regardless of how much power it has in reserve. Since the pad`s rotational speed is a function of the stroke and orbital speed, if a weak machine and a strong machine both have a 5/16th`s stroke and both are able to maintain a consistent orbital speed of 6800 OPM, the both will spin the pads at the same exact speed.

If pressure is applied, but neither machine looses speed, then even under pressure, both machines will perform the same.

The only advantage you are likely to see is under extreme down pressure, enough to actually cause significant drag on the orbital motion. In this case the stronger machine will maintain more orbital speed, which will will make the pad want to spin more. However at this pressure level it is very likely that the pads have stopped spinning anyways (it takes a lot to bog the orbital motion action of a machine. I know it sounds like they bog (changes in noise) but the actual change is speed is very very little.

Enough theory for one day, I`m exhausted!

**Todd@RUPES** · 04-23-2011, 05:36 PM

Oops, one more thought...

"Does rotational speed matter for correction?"

This depends on how effiecent the pad is at transfering the orbital motion of the DA to the paint.

A big foam pad will act like sponge and jiggle on itself which absorbs a lot of the action. The machine may move the backing plate in a 5/16ths` orbit, but after that is motion is absorbed in the internal flexation of the pad, it is possible that only 2/16th (if any) of the motion makes it to the paint. A bowl of Jello jiggling on itself.

In this case rotational speed is very important since most of the action (the pad moving against the paint causing friction) comes from the spinning (RPM). With a very inefficient pad design you basically turn your DA into a slow speed rotary.

With an efficient pad design (think thin, smaller diameter) much more of the orbital motion and friction is transferred to the paint. In this case rotational speed is far less important since a lot of the polishing friction is coming from the orbital action.

I hope I haven`t confused anybody with a trip inside my disorganized brain.

**Deep Gloss** · 04-23-2011, 06:15 PM

There you go again Todd... Dropping science like Galileo!!

Sent using Tapatalk

**BIOLINK** · 04-23-2011, 06:34 PM

Originally Posted by th0001

I hope I haven`t confused anybody with a trip inside my disorganized brain.

ut:

Not at all. Wait, what was the question?

**imported_Stokdgs** · 04-23-2011, 06:52 PM

I have found that I need to run my Meguiars G110V2 at Speed-6 to get rotation the best, and this is fine for smaller areas where the smaller 4" pads work best, and as been already said, the smaller the pad, the better the rotation, as well as the thinner the pad, etc...

Believe the Griot/Shurhold machine rotates the best, which is why so many people are buying that/those models, and PAC believe still sells the Shurhold model..

Guess next we will be reading about you using the new Meguiars microfiber pads, compounds with your machine and having great success?

DanF

**PorscheGuy997** · 04-23-2011, 07:28 PM

Just to add...

Rotation does not always mean that you will be correcting. If one barely places the pad on the paint (negative pressure), the pad will spin like crazy and accomplish almost no defect removal.

With microfiber pads, a user can place a lot of pressure on the machine and really start to remove some serious defects. Some of the best results I have achieved were when the pad was barely rotating. Just be sure to keep the speed around four.

**imported_glfahlc** · 04-23-2011, 08:55 PM

Originally Posted by PorscheGuy997

Just to add...

Rotation does not always mean that you will be correcting. If one barely places the pad on the paint (negative pressure), the pad will spin like crazy and accomplish almost no defect removal.

With microfiber pads, a user can place a lot of pressure on the machine and really start to remove some serious defects. Some of the best results I have achieved were when the pad was barely rotating. Just be sure to keep the speed around four.

as a matter of fact i have used the 5.5 microfiber pads and the 5" tangerine and crimson pads. mind you i did get great correction but was just wondering just how important rotation was as i put a mark on my backing plate and was getting very little rotation with very little pressure at less than 5.5 on the 7424xp.

todd thanks for tech speak but i have to read it again and again so i can comprehend just what you`re telling us. i know its important.

**Todd@RUPES** · 04-23-2011, 09:29 PM

Originally Posted by glfahlc

as a matter of fact i have used the 5.5 microfiber pads and the 5" tangerine and crimson pads. mind you i did get great correction but was just wondering just how important rotation was as i put a mark on my backing plate and was getting very little rotation with very little pressure at less than 5.5 on the 7424xp.

todd thanks for tech speak but i have to read it again and again so i can comprehend just what you`re telling us. i know its important.

Sorry let me make it easier for myself to understand

With a large, inefficient pad rotation is very important since the spinning (like a rotary) is the only action effecting the paint.

With an efficient pad (small, thin) rotation isn`t as important because the orbital action plays a greater role.

**bmw5541** · 04-23-2011, 10:39 PM

Dr. H, you did it again.

I love the way you break things down and make it easier for all to understand. I really enjoyed reading your responses.

**imported_glfahlc** · 04-24-2011, 09:45 AM

Originally Posted by th0001

Sorry let me make it easier for myself to understand

With a large, inefficient pad rotation is very important since the spinning (like a rotary) is the only action effecting the paint.

With an efficient pad (small, thin) rotation isn`t as important because the orbital action plays a greater role.

thanks todd for making that clearer for the non-engineers among us, but i like reading your tech speak too...