A reader recently asked if he could use an angle grinder in place of a dedicated polisher to polish his car.

It's a great question and often one that's often blurred especially with the myriad of polishing attachments for drills coming out from China Inc. Since we're covering this subject, we decided to also touch on both the drill and the sander as a polishing tool as well.

It's tempting to think you can replace an expensive polisher with something a fraction of the cost.

The Bosch GPO12CE has a retail price of over RM650 while the Hitachi SP18VA and Makita 9237C comes in at RM620 and RM930 respectively. While a Bosch GMB350 electric drill or a Bosch GWS060 4-inch angle grinder by comparison retails for less than a third of those polishers! 

It all depends on how you spin it:

Technically, all these tools, polishers, grinders, drills are all rotary tools - they spin in one axis and in one direction and as long as you can purchase a backing plate adaptor with a hook and loop for the drill or angle grinder, you're in business.

In the car detailing industry, these polishers are known as a rotary polisher. A more elaborate (and expensive) random orbital or dual-action (DA) polishers produces a more gentle finish (read: less heat) as it's almost impossible to burn through the clear coat even if you're inexperienced or careless.

Speed kills your paint.

The problem with using an angle grinder for polishing your car is the rotational speed. Angle grinders, with the exception of the variable-speed grinders, such as the Bosch GWS8100CE, typically work on one set speed, typically around 9,000rpm to 12,000rpm to either grind or cut.

As such, your car could very well look like the DeLorean from Back To The Future (for a short while before rusts sets in) as the angle grinder polishes every last bit of paint and primer to the metal surface.

Grinders versus polishers.

For the sake of technical similarities, we will compare the Bosch GWS13125CI 5-inch angle grinder to the Bosch GPO12CE polisher. Both come with an M14 spindle thread and almost similar 1,250-watts to 1,300-watts power output.

The GWS13125CI has a no-load speed of 11,500rpm while the GPO12CE has a variable, no-load speed of 750rpm to 3,000rpm.

Right off the spec sheet, you can see that the GPO12CE gives you more control over the GWS13125CI in terms of speed control which is very important in achieving the desired surface finish.

Wait a minute.. You mentioned the variable-speed Bosch GWS8100CE grinder, would that work as a polisher?

In a pinch, it is possible. The GWS8100CE is a 850-watts, 4-inch angle grinder with an M10 spindle thread with a variable, no-load speed of 2,800rpm to 11,000rpm.

While most polishers have an M14 spindle thread, you could probably use an M10 to M14 adaptor and remove the guard to enable you to use bigger 5- to 7-inch polishing pads.

Unfortunately, even at its lowest speed, the GWS8100CE still spins at 2,800rpm, almost the maximum speed of the GPO12CE and it's still some 400-watts down on power so it might also bog down with bigger polishing pads.

Okay, so can a polisher be used as a grinder instead?

At this point, you're probably thinking, "Wow, that means I can strap on a grinding disc and use my GPO12CE as a variable-speed angle grinder!" ..and yes, you are perfectly right.. Except, that you might sacrifice some digits in the process as the GPO12CE doesn't have a guard.

So what about drills as polishers?
Depending on the size of the drill chucks, drills typically only accept bits from 6mm to 10mm. So there might be a 'bit' of a problem finding a 5-inch backing pad or a 6-10mm bit to M14 spindle thread that fits.

Even if China Inc came out with something of that nature, you would have a really tough time controlling the pad due to the interial forces exerted on the pad.

Also, since electric drills have a trigger-operated speed mechanism, trying to achieve consistent polishing speed can be very tricky. So don't do it!

The only convincing workaround exception to using an electric drill for polishing your car we've seen so far is the Meguiar's DA Power System Tool a dual-action polishing drill attachment. 

The Meguiar's system turns your drill's rotation into an orbital motion through gearings and addresses the inertial forces generated by the polishing pad by attaching a handle to the gear housing. Unfortunately, that attachment alone costs more than half a Bosch GPO12CE and is not compatible with standard hook and loop pads on the market.

But if that's the case, why do I see so many Chinese-made polishing pads for drills?

Now here's where it all gets muddled, you can find quite a few Chinese vendors selling polishing pads that fits perfectly in a 10mm drill chuck - we also carry a Visbella Headlight Restoration Kit that comes included with a hook and loop polishing pad that accepts both the sanding and polishing pads.

For 2-inch or small pads, working on small surfaces such as the headlights, it is possible to use a drill as a polisher. It might not be the perfect solution, but perfect for the sake of convenience.

What about orbital sanders?

Fine sanding and polishing has similar orbital motion which 'almost' makes the orbital sander perfect for a dual-action polisher substitute. In fact, the modern dual-action polishers are descendants of the orbital sanders.

Additionally, some electrical orbital sanders are also equipped with a variable-speed setting complete with a 5-inch hook and loop backing plate - making it again almost perfect for automotive paint detailing.

The catch with orbital sanders? 

Most orbital sanders move at a very rapid pace for material removal, the Bosch GEX1251AE for example, starts life at 7,500rpm and spins all the way to 12,000rpm - even at the slowest speed, it's more than double what most polishers can do.

Orbital sanders are also relatively low-powered so they might bog down when used to remove paint defects with a foam pad and would only vibrate about without getting any work done.

Sanding is sometimes used in the auto-detailing industry to remove a very thin layer of uneven clear coat, otherwise known in the industry as "orange peel" or badly scratched or oxidised clear coat but sanding clear coat is always done with a very fine sandpaper grit with a lot of water as lubrication and at very low speeds.

While an orbital or dual-action motion is more gentle on the paint, it's generally considered way too fast. Also, while the backing plate that comes with the orbital sander has a hook and loop attachment, it's often too stiff for polishing paint.

Our advice?

Unless you're planning on only using it for a specific task once, grab the right tool for the job. It would yield a much better results and make the task a whole lot more enjoyable!

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