Many unbreakable plastic watch crystals are made of tough acrylic plastic that can be susceptible to scratches. Don’t just throw out your old crystal when you start to see scratches on it, use this guide to polish those marks away with any tool that uses a rotary motor, from stationary polishing motors to hand held motors like the flex shaft or micro motor.
Be aware that you can only polish away scratches. If your crystal is chipped or cracked you cannot fix it by polishing and you will have to replace it completely. Also if your crystal is very thin you will have to be careful about how much you polish. Check out this link to learn How to Replace a Watch Crystal.
- A rotary motor, polishing motor or a flex shaft
- A soft muslin buffing wheel: 4″ size for the polishing motor and 1″ size for the flex shaft
- Crystal polishing compound bar
- A pair of safety glasses
- Polyimide tape or masking tape
- Soft crystal cleaning cloth
The first thing you should do is prepare your watch for polishing. To protect the finish on the watch case while you buff the watch crystal, you will want to take your polyimide tape and use small pieces about an inch and a half long to cover the metal around the crystal. Overlap the pieces of tape to completely cover the metal around the watch crystal and give your watch the illusion of having a mane.
Once you have covered all the metal, set the watch aside and set up your buffing system. And remember, before you start up either motor, be sure to first put on your safety glasses to protect your eyes from flying debris.
If you are working with a polishing motor: Attach your four inch soft muslin buff to the motor spindle.
If you are working with a flex shaft or other hand held motor: Attach your one inch muslin buff to the hand tool of the motor.
Before you can start actually buffing and polishing the crystal, you need to apply a thin layer of your crystal polishing compound to the spinning buffing wheel. Start the motor turning and allow the buff to begin spinning, once it is operating at normal speed, you will apply the compound to the buff. For the polishing motor it is easiest to bring the compound to the buff, whereas with the flex shaft it is easiest to bring the buffing wheel to the compound, unless you are using the hand tool with a third hand to hold it in place.
Either way, hold the compound and buffing wheel together with medium-light pressure for approximately two seconds. This should give you a nice and even coating of compound across the wheel. Try to avoid over applying the compound to the wheel, too much compound can be just as detrimental and inefficient as using too little compound.
Next, take your watch with its protective tape mane and hold the watch securely in your hand with the crystal facing up. Keep your fingers away from the edges of the crystal and hold it securely to keep it from slipping or from injuring yourself while you work.
Press the crystal against the buffing wheel with light to medium pressure and keep it moving against the buff so that you don’t over polish one portion of the crystal. The crystal’s top should face directly toward the buff to maintain existing crystal shaping. However always keep changing the position of the crystal against the buff to avoid unnecessary wear on the buff and the crystal. This will also ensure that you can polish each edge of the crystal equally. You may find it easier to bring the flex shaft’s handheld buff to the crystal and keep the watch case steady.
Stop frequently and take the buffing wheel away from the crystal to check your progress and make sure that you are not over polishing any particular section.
Then, after you get a feel for how your buff is working with your plastic crystal, you can increase the pressure between the wheel and the crystal to work more quickly. However, be careful not to let the crystal overheat while you work: take breaks whenever the crystal starts to get hot to the touch.
Continue polishing and checking your progress, repeating Steps 3 and 4 until you can no longer see the scratches on the surface of your crystal.
Then, take your soft cleaning cloth and use it to remove any excess polishing compound from the face of the crystal and any remaining adhesive from the watch case.
When that is complete, your crystal should look just like new and you can start wearing it again. For other handy methods for polishing watch crystals, check out our Learning Center for more articles.