# Spot pads on a DA 'can' be dangerous!



## Guest (Apr 20, 2010)

There are some people on this site who make it sound like you can't hurt your cars paintwork with a DA or that it's difficult to. Well I assure you this is not the case.

Today while correcting some paintwork, namely scratches around a door handle, I made the paint get very very warm. I had not previously used spot pads to the extent I had today. It was somewhat accidental that I realised the heat on the paint and thankfully I did. 

I had not known that you could achieve this in such a short space of time with spot pads. I had not come across with 5.5"-7" pads.

I wanted to let others know who were not already aware of this. Spot pads are very effective and give better results in a shorter time, but for me I'll be checking paint temperature regularly when using them.


----------



## Will-S (Jun 5, 2007)

Due to their smaller size the rotation of spot pads is higher. This in turn means the heat build up is quicker. As you correctly state, care must be taken with spot pads for this very reason.


----------



## Alan W (May 11, 2006)

Will-S said:


> Due to their smaller size the rotation of spot pads is higher. This in turn means the heat build up is quicker. As you correctly state, care must be taken with spot pads for this very reason.


This is not true I'm afraid. The velocity of the outer edge of a larger 5.1/2" or 6" pad is travelling much faster for a given speed (say 1500 rpm) than a spot pad. Work out the circumference of each pad times the machine speed and you'll see what I mean!

I'm not inplying that a spot pad *can't* damage paint just that the statement by Will-S is *not* correct.

Alan W


----------



## Reflect (Dec 10, 2009)

Alan W said:


> This is not true I'm afraid. The velocity of the outer edge of a larger 5.1/2" or 6" pad is travelling much faster for a given speed (say 1500 rpm) than a spot pad. Work out the circumference of each pad times the machine speed and you'll see what I mean!
> 
> I'm not inplying that a spot pad *can't* damage paint just that the statement by Will-S is *not* correct.
> 
> Alan W


I was under the impression that this were more true for the rotary. I thought with a PC and a spot pad and its oscillation and lack of power that the smaller pads generate more cut. I was under the impression that the rotary and PC acted contrarily with pad size.


----------



## Will-S (Jun 5, 2007)

This was my understanding too. Saw this first hand when on a tuition day. small pad created burn through on panel. Alan-W you may well be right and my experience on tuition day was exagerated by the trainer


----------



## trebor127 (Aug 13, 2009)

It may not be turning as quick, but the pressure is concentrated on a smaller area....


----------



## Alan W (May 11, 2006)

Reflect said:


> I was under the impression that this were more true for the rotary. I thought with a PC and a spot pad and its oscillation and lack of power that the smaller pads generate more cut. I was under the impression that the rotary and PC acted contrarily with pad size.


Yep, I was thinking this was a rotary!  I don't have the mathematical knowledge to work out how this would differ with a DA but your understanding of it being contrary to a rotary may well be true.

Alan W


----------



## Alan W (May 11, 2006)

Will-S said:


> This was my understanding too. Saw this first hand when on a tuition day. small pad created burn through on panel. Alan-W you may well be right and my experience on tuition day was exagerated by the trainer


Sorry Will but as I've posted above my theory only holds good for a rotary. I didn't read the OP's question properly!  A DA is a completely different animal and Reflect could be right about the contrary theory.

The only thing I would add is that if the DA was not a forced rotation type (like a Flex) surely the clutch would come in to play and stall the pad if heavy pressure were exerted on the machine?

Alan W


----------



## Dodo Factory (Apr 11, 2007)

Heat build up may be more concentrated with spot pads. Also, could they not potentially rotate more than a larger pad due to lower surface area per given speed? Less drag on the panel? May be wrong with that - just a theory that popped into my head, but heat is certainly something to watch out for.


----------



## DBSK (Apr 22, 2008)

Dodo Factory said:


> Heat build up may be more concentrated with spot pads. Also, could they not potentially rotate more than a larger pad due to lower surface area per given speed? Less drag on the panel? May be wrong with that - just a theory that popped into my head, but heat is certainly something to watch out for.


A very valid point i think, i only use 4" pads as opposed to 6" now, as the 6" is too big of an area for my G220 to get spinning with the clutch.

The 4" gets much better correction as there is less friction allowing the pads to spin more freely with any sort of pressure.


----------



## Alan W (May 11, 2006)

Dodo Factory said:


> Heat build up may be more concentrated with spot pads. Also, could they not potentially rotate more than a larger pad due to lower surface area per given speed? Less drag on the panel? May be wrong with that - just a theory that popped into my head, but heat is certainly something to watch out for.


Not sure Dom. Given that heat is created by friction, a larger pad (in theory) should create more friction, and hence heat, for the same speed and force on the machine.

Alan W


----------



## Dodo Factory (Apr 11, 2007)

I think it is to do with the heat dissapation throughout the pad. I have found them runner hotter through experience, but me experience is limited a bit with DAs. Maybe some more scientific tests need to be done.

Spot pads do seem more dangerous though - I get much worse hologramming with spot wool pads than larger ones for example, which is odd as the outside of a larger pad DOES travel faster...


----------



## Dodo Factory (Apr 11, 2007)

David King said:


> A very valid point i think, i only use 4" pads as opposed to 6" now, as the 6" is too big of an area for my G220 to get spinning with the clutch.
> 
> The 4" gets much better correction as there is less friction allowing the pads to spin more freely with any sort of pressure.


Maybe it is a torque/turning force issue.

Motor is say 500W. Pad has a certain amount of friction per sq cm. Therefore less likely to stall at a certain power setting. If less likely to stall, pad will therefore increase in speed before clutch effect (assuming DAS machine) will step in and protect the paint.


----------



## karl_liverpool (Sep 25, 2008)

its frowned on a bit here but i like to make sure the pad is well lubricated with the polish. an old school painter stunned me when he showed me the finish he could achieve with just water and a polishing pad.

in my mind now the pad does the majority of the work with its construction. the polish is just a sort of lubricant which has a bit of bite to it.


----------



## Alan W (May 11, 2006)

Dodo Factory said:


> Maybe it is a torque/turning force issue.
> 
> Motor is say 500W. Pad has a certain amount of friction per sq cm. Therefore less likely to stall at a certain power setting. If less likely to stall, pad will therefore increase in speed before clutch effect (assuming DAS machine) will step in and protect the paint.


That certainly sounds a good theory for the greater friction and hence heat.

Now all we need is for someone to confirm it or tell us we're all wrong! :lol:

Alan W


----------



## mwbpsx (Jun 23, 2006)

I dont know the physics but, on a da the smaller the pad the more agressive , on a rotary its the opposite

Mark


----------



## Guest (Apr 20, 2010)

David King said:


> A very valid point i think, i only use 4" pads as opposed to 6" now, as the 6" is too big of an area for my G220 to get spinning with the clutch.
> 
> The 4" gets much better correction as there is less friction allowing the pads to spin more freely with any sort of pressure.


Yes; while correcting with the spot pad I could certainly use a lot more force than I could with the 5.5" or 7". I remember now that when I went to change the pad I felt it was warm so I touched the paintwork and it was much warmer. 
Decided to leave it as I had achieved a very good level of correction anyway. I could have gone further and let it cool down first but it put me off a bit to be honest. I have never felt any of my other pads get warm before.

I have a Milwaukee rotary on order too so I expect I should get use to paint behaving in this way?


----------



## PaulN (Jan 17, 2008)

When people go on about its easier to control a 3" pad and some use it for the whole panel its a little scarey.

My thought would be small pads dont need as much pressure as larger pads, but are treated the same on a DA so the correction is faster but this is not always ideal.

I guess its like being on a snowboard in deep snow..... no problem as your weights evenly distributed, but take off the board and you go waste deep with the added local pressure.

It would be great to get a "cut in stone" view on the whole pad size for Da and rotary, but my view is if i goto a smaller pad i goto a less aggressive one from the 5" That way Ill never up the cut with the pad change.

Cheers

PaulN


----------



## M.J (Mar 17, 2010)

was chatting to caledonia on his class about this on sunday from memory the theory goes for a da the smaller the pad the more heat build up is likely due to the pad being in contact more regulary at a specific point ..... i may have this wrong 

the rotary however would work out less as the pad isnt traveling as fast ?? do i have this right? , i,m a newbie in machine polishing and dying to get started , hope i got my facts right lol


----------



## Alan W (May 11, 2006)

M.J said:


> was chatting to caledonia on his class about this on sunday from memory the theory goes for a da the smaller the pad the more heat build up is likely due to the pad being in contact more regulary at a specific point ..... i may have this wrong
> 
> the rotary however would work out less as the pad isnt traveling as fast ?? do i have this right? , i,m a newbie in machine polishing and dying to get started , hope i got my facts right lol


That's correct! :thumb:

Spot pad on a DA will provide greater cut/correction than a larger pad whilst the converse is true for a rotary where the smaller pad has a lower peripheral velocity and hence reduced cut/correction compared with a larger pad.

Alan W


----------



## PaulN (Jan 17, 2008)

Something i found out quickly is you really need to up the speed on a rotary when using a spot pad but didnt have to on the DA...... I guess the pressure makes a big difference.

Cheers

PaulN


----------



## TOGWT (Oct 26, 2005)

The smaller the diameter of the pad the more kinetic (heat) energy is transferred to a given area of the paint surface, due to their different surface area of the pads (Area = n (r2) ( 6-inch = 28.26 sq.ins /4-inch = 12.46 sq.ins ) The amount of applied pressure will also affect the kinetic friction (heat) energy transferred


----------



## MrD06 (Mar 22, 2006)

you have to go some to heat up a pannel though with a DA

if you are heating it up that much you are doing it wrong imho.

I only ever use 4" pads I think they are easier to use on curved pannel cars (which is most cars these days)

but to heat it up you must be pushing hard and not moving the pad,
Let the polish do the work and move the unit around breaking down the polish.


----------



## Alan W (May 11, 2006)

MrD06 said:


> you have to go some to heat up a pannel though with a DA
> 
> if you are heating it up that much you are doing it wrong imho.
> 
> ...


I tend to agree but plastic panels without much mass, small painted grilles and fairings, scoops etc, can heat up quite quickly. 

Alan W


----------

