Trend: Small buffing pads

This is very interesting stuff. I mentioned in another thread how technology is ever changing in this is a prime example. On the back of a Meguiar’s M105 bottle, the instructions for rotary applications tell us to set the RPM’s to 1500-2000. Making the assumption that we are using a 7” pad (because they don’t specify), and using the formula (RPM / 3.82 x Dia = SFM) then a RPM of 1200 equals a SFM of 2748.

SFM = Surface Feet Per Minute
RPM = Revolutions per Minute
Dia = Pad Diameter

If we make the same calculations for a 4” pad keeping the same RPM our SFM drops to 1570. (Almost in half.) The closer we approach 0 the further we drop on SFM. (Dead center is essentially spinning at 0 RPM.) The different abrasive technology used in different products must have a sweet spot. Specifying a RMP is getting way to ambiguous now days. We would need to set our RPM to 2624 in order to maintain the SFM of 2748.

Craig
 
cgreen1120 said:
Specifying a RMP is getting way to ambiguous now days. We would need to set our RPM to 2624 in order to maintain the SFM of 2748.

Craig
Click to expand...


Not sure about all the math but we used 3" wool cutting pads on rotary buffers on the 1963 Impala during my detailing boot camp class over the weekend to remove sanding marks around the 600 RPM to 1200 RPM range and they worked perfect.

We also used the 3" wool pads on the 1969 AMX we wetsanded out in Lincoln Nebraska and same thing, I did most of the intricate cutting with the rotary buffer and never buffed over 1500 RPM and would say that most of my cutting or compounding was don around the 1000 RPM Range.

Keep in mind I try to always finish out with #3000, #4000 or #5000 grit discs and use high quality compounds.


:)
 
cgreen1120 said:
This is very interesting stuff. I mentioned in another thread how technology is ever changing in this is a prime example. On the back of a Meguiar’s M105 bottle, the instructions for rotary applications tell us to set the RPM’s to 1500-2000. Making the assumption that we are using a 7” pad (because they don’t specify), and using the formula (RPM / 3.82 x Dia = SFM) then a RPM of 1200 equals a SFM of 2748.

SFM = Surface Feet Per Minute
RPM = Revolutions per Minute
Dia = Pad Diameter

If we make the same calculations for a 4” pad keeping the same RPM our SFM drops to 1570. (Almost in half.) The closer we approach 0 the further we drop on SFM. (Dead center is essentially spinning at 0 RPM.) The different abrasive technology used in different products must have a sweet spot. Specifying a RMP is getting way to ambiguous now days. We would need to set our RPM to 2624 in order to maintain the SFM of 2748.

Craig
Click to expand...


Let me start off by stating that math is not my forte. I graduated with a GPA slightly higher than W (43), so I'm not the brightest bulb in the pack.

OK. I'm thinking that the fallacy of your argument lies in the fact that SFPM refers to the outside diameter of the "wheel", as opposed to diameter of the "pad" face. Hope this makes sense.

Help me to understand your position as I personally feel that if you set the rpm to your specs (which the Flex PE14 cannot attain btw), you're going to see tremendous heat buildup rather quickly, excessive sling of product, limited correction, and finally, burn through on leading edges and raised panels. TIA :) !

 
Your math skills are fine. This formula is used in the metal machining industry on a daily bases and has been for many years.
It does not matter if it is the outside diameter of the pad or the face. RPM must be calculated using a diametrical value. When the machine manufacture calibrated the equipment, they used either the center arbor itself or a backing plate or even maybe a specific pad diameter, I’m not sure. My thought is that they use the machine spindle for there calibration. If this is true then the math look like this.
RPM / 3.82 x Dia = SFM

600/3.82 x 5/8 = 98 SFM (5/8” arbor)

If we use a 7” pad, the math come out to….

600/3.82 x 7 = 1099 SFM (7” pad)

As you can see, we never changed the RPM but the bigger we get the higher the surface footage gets thus more friction and heat. Different abrasive technologies have different requirements for effective cutting and that is what I am trying to better understand.

I face the problem daily that my machine spindles cannot obtain the RPM’s recommended by tooling manufactures. That doesn’t change the math. I must compensate in other ways. Heat from friction is directly related to the amount of surface contact and as we reduce our pad diameter the surface contact and heat are reduced. If you turn your Flex on its back and turn the RPM all the way up, you will observe that you can almost count the rotations at the center of the pad but the further you depart from center, the faster the surface of the pad appears to go. In machining, we compensate for this by keeping a constant surface footage by increasing our RPM’s as we approach the center of the material. You will in fact get less heat, burn through and correction on a 3” pad turning 600 RPM than you would get on a 7” pad turning the same speed. In either case you will get NO correction at dead center because it is in fact NOT turning. If the pad design does not retain the product well, you are correct in say it will have excessive slinging. This will cause loss of lubrication and result in heat buildup. (Now we get a burn through.) In my opinion, you can’t just make a smaller pad and call it good. You must factor all these things into your design.

My prediction is that Mike’s next book will be entitled “The Art and Science of Detailing”. Technology in this industry is changing so rapidly that science will have to take a more active role or we will be doing more test spots and product testing than actual detailing.

Craig

p.s. These are great discussions.
 
On my short ride to Connecticut today I had another thought. What about the amount of down pressure? The surface area of a 7” pad is roughly 38.485 and a 3” pad is 7.069. The 7” pad has 5.444 times the area to distribute the down force. If we exert 15lbs. of down force on the 7” pad we will probably see very little effect but put the same down force on the 3” pad and I think we all know what the outcome will be.
As the amount of surface contact diminishes the amount of down force must be reduced exponentially by a factor determined by pad size, pad density and panel shape. This concept holds true when we depart from flat surfaces to irregular surfaces’ and shapes. When we come to a hard body line that is not masked off we risk putting the entire down force on a single point of contact. This point is already thin as far as clear coat goes but now we have little or no distribution of friction. As the pad size is reduced we are better able to keep constant contact and distributed pressure a little more consistently so long as we watch and anticipate machine and pad motion.

Just a thought,
Craig
 
Im the MAN
cgreen1120 said:
Your math skills are fine. This formula is used in the metal machining industry on a daily bases and has been for many years.
It does not matter if it is the outside diameter of the pad or the face. RPM must be calculated using a diametrical value. When the machine manufacture calibrated the equipment, they used either the center arbor itself or a backing plate or even maybe a specific pad diameter, I’m not sure. My thought is that they use the machine spindle for there calibration. If this is true then the math look like this.
RPM / 3.82 x Dia = SFM
I use this whenever I use greaseless and varying sized wheels.

How To Buff And Polish - Caswell Inc

600/3.82 x 5/8 = 98 SFM (5/8” arbor)


If we use a 7” pad, the math come out to….

600/3.82 x 7 = 1099 SFM (7” pad)

As you can see, we never changed the RPM but the bigger we get the higher the surface footage gets thus more friction and heat. Different abrasive technologies have different requirements for effective cutting and that is what I am trying to better understand.

I face the problem daily that my machine spindles cannot obtain the RPM’s recommended by tooling manufactures. That doesn’t change the math. I must compensate in other ways. Heat from friction is directly related to the amount of surface contact and as we reduce our pad diameter the surface contact and heat are reduced. If you turn your Flex on its back and turn the RPM all the way up, you will observe that you can almost count the rotations at the center of the pad but the further you depart from center, the faster the surface of the pad appears to go. In machining, we compensate for this by keeping a constant surface footage by increasing our RPM’s as we approach the center of the material.

Detailing is more forgiving, and not quite exact. IMO, it doesn't quite work this way in paint correction. Paint as a whole is soft and most of the correctable imperfections are shallow. While proper speed - which is one proponent - is desired, it's not neccessary. One can correct by hand, but of course machines are not only quicker, but consistent.

You will in fact get less heat, burn through and correction on a 3” pad turning 600 RPM than you would get on a 7” pad turning the same speed. In either case you will get NO correction at dead center because it is in fact NOT turning. If the pad design does not retain the product well, you are correct in say it will have excessive slinging. This will cause loss of lubrication and result in heat buildup. (Now we get a burn through.) In my opinion, you can’t just make a smaller pad and call it good. You must factor all these things into your design.

My prediction is that Mike’s next book will be entitled “The Art and Science of Detailing”. Technology in this industry is changing so rapidly that science will have to take a more active role or we will be doing more test spots and product testing than actual detailing.

Craig

p.s. These are great discussions.
Click to expand...

Thanks for posting. I ask a lot of dumb questions on these forums, and will make dumb comments. But this is part of my process in learning this craft.
I've been using the 9227 as of late, and like Mike reported, I too lower my speed when dropping down to smaller pads with an extension, regardless of product. And even moreso when correcting paint in intricate areas. It's not so easy to control a rotary @ higher rpms while laying on your side polishing bumper facial, air dams, and cut-outs.

cgreen1120 said:
On my short ride to Connecticut today I had another thought. What about the amount of down pressure?

81 is one of my favorite 4 lanes on the east coast. Hopefully Mike will get back to you on this, but generally I use the weight of the machine itself, or with slightly added pressure depending on whether compounding or polishing, and pad ability to tackle issues.

The surface area of a 7” pad is roughly 38.485 and a 3” pad is 7.069. The 7” pad has 5.444 times the area to distribute the down force. If we exert 15lbs. of down force on the 7” pad we will probably see very little effect but put the same down force on the 3” pad and I think we all know what the outcome will be.
As the amount of surface contact diminishes the amount of down force must be reduced exponentially by a factor determined by pad size, pad density and panel shape. This concept holds true when we depart from flat surfaces to irregular surfaces’ and shapes. When we come to a hard body line that is not masked off we risk putting the entire down force on a single point of contact. This point is already thin as far as clear coat goes but now we have little or no distribution of friction. As the pad size is reduced we are better able to keep constant contact and distributed pressure a little more consistently so long as we watch and anticipate machine and pad motion.

Just a thought,
Craig
Click to expand...

I think correction is more of an art than science, not trying to be argumentative. There are so many variables that one can choose and still achieve perfection. Whether product selection, pad ability, down force, speed, etc. There is no cookie cutter approach with the myriad of variables offered in correction.

Seems that the Raven's mojo went out with the lights. I hope they get it back quickly.
 
Vegas Transplant said:
Thanks for posting. I ask a lot of dumb questions on these forums, and will make dumb comments. But this is part of my process in learning this craft.
I've been using the 9227 as of late, and like Mike reported, I too lower my speed when dropping down to smaller pads with an extension, regardless of product. And even moreso when correcting paint in intricate areas. It's not so easy to control a rotary @ higher rpms while laying on your side polishing bumper facial, air dams, and cut-outs.

I think correction is more of an art than science, not trying to be argumentative. There are so many variables that one can choose and still achieve perfection. Whether product selection, pad ability, down force, speed, etc. There is no cookie cutter approach with the myriad of variables offered in correction.

Seems that the Raven's mojo went out with the lights. I hope they get it back quickly.
Click to expand...

Not that I can add anything of real meaning here. :doh:
Just wanted to touch on these two points. As Mike mentioned, tippy is an issue. Now I'm just using the GG, with 4" pads but the experiments so far have been worth the effort. Especially as the only other way to get at a lot of the places where the smaller pad work is by hand, and a LOT of work at that.

Perhaps that 2nd paragraph there is a different way of saying "do your test spot". ;)

And as far as the Raven's, looks like somebody made side bets during the blackout! :rolleyes:
 
cardaddy said:
Not that I can add anything of real meaning here. :doh:
Just wanted to touch on these two points. As Mike mentioned, tippy is an issue. Now I'm just using the GG, with 4" pads but the experiments so far have been worth the effort. Especially as the only other way to get at a lot of the places where the smaller pad work is by hand, and a LOT of work at that.

Perhaps that 2nd paragraph there is a different way of saying "do your test spot". ;)

And as far as the Raven's, looks like somebody made side bets during the blackout! :rolleyes:
Click to expand...
That's what I was thinking:xyxthumbs:
Your opinion is of high regard forum member. I've yet to use a smaller pad set-up on a da, Cyclo excluded of course.
But I think the subject pertains to rotary/small pads since sfpm's are the focal point of the Commonwealth hand's statement.

In regard to the second paragraph, my intent was to show that machining is a science with stringent tolerances. Paint correction is rather loose. Kinda comparing apples to oranges.

My words don't always convey my thoughts. I'm more addicted to AGO than I am to detailing.
 
My intent has never been to argue, only to provoke deeper thought and good discussions. I agree that paint correction is an art but without understanding why things are what they are it becomes a black art. When I started machining metal way back when, it was done primarily by manual machines and was considered an art. The need for higher productivity and profits brought us the computer numerical control (CNC), computer aided manufacturing (CAM) software, ceramic and carbide cutting tools with a plethora of different coatings and many other technologies. The art of machining metal will never go away because like paint correction, the variables are endless. I have to rely on my 30+ years of machining metal to insure the best possible outcome on every part we produce and I do consider it my craft. Mike and many others here on Auto Geek Online rely on their many years of experience (and generously share) to produce the best possible corrections. By understanding a little of the science, it gives the rest of us some good starting parameters and removes a little of the black from the Art of Detailing. With well over 2700 views on this thread, I know we have some people thinking and hopefully some of them are from the manufactures of the products we use and the paint industry.
 
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