How can you avoid "pigtails" when machine sanding?

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Kaban

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Hi Mike,

I was wondering if you had any input on this (I am sure you do).

Lately I've been machine sanding on scrap panels, old headlights, etc...

I am using a Metabo orbital sander (looks very similar to the Griot's 3" DA).

I have a small backing plate on it (about 3") and a 3M interface pad, which is a soft foam layer between the backing plate and the actual sanding disc.

I've been doing 180>320>600>800>1000>2000 on various headlights I had access to to practice. Basically, I am getting pigtails when using the coarse sanding disks which are the 180 and 320. From 600-2000 I am wetsanding with the machine.

It's so frustrating, because you can't really see the pigtails after you do a pass with the machine and do a wipedown... but after I compound the lens with a wool pad and some menz. power gloss and finish it with SIP and 85rd, in some spots you can see the pigtails reappear.

Is it my technique with the sander? I am using it at the highest speed and changing discs after every pass so they dont get clogged.

I'd really appreciate any tips Mike as I would like to avoid this in the future.
 
Imo....your using to sharp of paper, i polish lens all the time and i never ever use below 600 grit. I get great results every time.
 
Pigtails when sanding are the result of the paper becoming clogged with debris and this debris follows the oscillation pattern of the machine...

The faster the machine speed the more friction hen more heat. The heat is melting the plastic and this is becoming stuck causing the pattern you describe...

I never use a machine when wet sanding headlight lenses. Try using only the finer grits and work by hand to see if this eliminates the problem.
 
Yeah I get what you're saying... these lenses had VERY deep scratches because the entire car was keyed... I mean these were hella deep and sanding them down by hand would have taken a decade. That's why I resorted to using a machine.
 
it does not sound like you are sanding enough with the finer grades. a pigtail shows the oscillation of the sander. you have the same marks with finer grits you just can not see them because there is more grit closer on the paper. jonathan
 
Great point ^ I was thinking the same thing. Maybe I should have followed up with 400 instead of jumping from 320>600 right away.
 
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