New Makita owner, burnt clear coat :(

E

eternalx88

New member
I was very confident in using my PC 7424 and so I was stupid and thought that I did not need any practicing with the Rotary and buffed my BMW M roadster. Boy was I wrong, I did the trunk lid no problem and then decided to work on my rear bumper. I burnt the edge of the rear bumper (sorry no pictures)



I was using speed setting of 3.25. Is this too fast? This is on a Makita 9337



I was using the Edge 2000 foam pads. They are big pads, do you recommend using a 4 inch pad for the rear bumper?



Finally, any advice on working with the Makita 9337...I guess I should of worked with a slower speed...
 
Trunk is metal, bumper is plastic. Plastic heats up WAY quicker than metal :)



and yes, it's better using smaller pads and less speed. I got some 6" pads and can't stand using anything larger. I find they're way too cumbersome and errors occur easier.



Don't feel bad about the burn through...happens to all of us.
 
9227? The 9337 is an air gun I think.



3.25 is over 1500 rpm; honestly I will buff hard paint at between 3 and 3.75 sometimes, but on a bumper, never. The rotary heats up paint and the underlaying structure much, much, much quicker than a PC, so that speed on a bumper probably literally melted the plastic/paint; I bet it lifted up like a candy wrapper, right?



A 4 inch pad would be even worse in terms of heat since it is more concentrated heat. It isn't worse to use them in general, but I wouldn't expect them to be easier to use on a bumper. What you need to do on bumper is more passes, moving the machine more quickly, at lower speeds. When I do bumpers I usually run the machine at a speed of 1200-1500 rpm max, I just make sure to do more passes.



There are literally dozens of "how to" threads on rotaries on this site and elsewhere, I'd definitely take the time to read them. It is not like using a PC.
 
stick with a PC on plastic panels- use the rotary with soft finishing pads and mild polishes on flat steel panels. Practice on some old beaters first.
 
4 inch are ok on plastic with rotary but keep speed down to 1200 and do the stop and start method.
 
Picus said:
A 4 inch pad would be even worse in terms of heat since it is more concentrated heat.
Click to expand...

:confused: Isn't the opposite true? The smaller the pad, the slower the outer edge moves at a given rpm. So the less heat it makes.



Sorry to hear about your bumper. Unfortunately I think many of us learn that way. Get it repainted and try to be more careful. It happens to everyone though at some point.
 
Aurora40 said:
:confused: Isn't the opposite true? The smaller the pad, the slower the outer edge moves at a given rpm. So the less heat it makes.



Sorry to hear about your bumper. Unfortunately I think many of us learn that way. Get it repainted and try to be more careful. It happens to everyone though at some point.
Click to expand...



No. The smaller the pad the faster the outside edge spins; it is also more concentrated heat because the pad's overall surface area is smaller.
 
Picus said:
No. The smaller the pad the faster the outside edge spins;
Click to expand...



I do think you are wrong about this



look at it this way if you have a 4" pad and a 8" pad

a point on the edge of the 8" pad will have to travel twice as

far durring the same RPM



so it will be moving about twice as fast
 
BigJimZ28 said:
I do think you are wrong about this



look at it this way if you have a 4" pad and a 8" pad

a point on the edge of the 8" pad will have to travel twice as

far durring the same RPM



so it will be moving about twice as fast
Click to expand...



You are right, the small the pad the less heat/aggressiveness..now with a PC it is the opposite, the smaller the pad makes it more aggressive.
 
Picus said:
No. The smaller the pad the faster the outside edge spins; it is also more concentrated heat because the pad's overall surface area is smaller.
Click to expand...





Some pretty basic mathemathics involved in this. A 4 inch pad has an outside edge circumference of 12.56"(2*pi*2"), travelling at a speed of 1200 rpm, would equal a distance of 15,072 inches in one minute.



A 6 inch pad has a circumference of 18.84", a speed of 1200 rpm, would equal 22,608 inches in one minute.



An 8 inch pad, and the distance traveled in the same amount of time would be even greater. Most of the heat is concetrated in the outer edges of a pad, because the further out you get, the faster the pad travels(for exmple, the inner 1" of the pad has an edge travel of 3,768" in one minute). A direct rotational device has different dynamics from an orbital device, which we know creates more heat with a smaller pad, the opposite is true of a rotary.
 
Can anyone say dynabrade orbital attachment?



Use that with an edge 6 inch pad system and you can remove almost any paint defect.



Derrick
 
4 inch pad on a pc is better because you're allowed to apply more force to that area. P=F/A, so applying the force will give you a greater pressure.



Careful with the makita though. 3.5 is pretty quick. I usually use 3.5 for about 2 passes and that's about it. Usually without pressure. I do most of my cutting on 3.
 
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