You set up your machine, turn on the motor, and grind the valve. You are expecting a mirror-like finish. But when you pull the valve out, it looks like the surface of a vinyl record. It has tiny waves, ripples, or rough lines across the face.
In the machining world, we call this "Chatter."
Chatter isn't just ugly. A rough valve face won't seal against the seat properly. It creates tiny gaps where hot gas can sneak through, which will burn the valve and ruin your work.
So, why does it happen? Chatter is almost always caused by vibration. Something is bouncing when it should be steady. Here are the four most common reasons chatter happens and how to stop it.
This is the #1 cause of bad finishes. As you grind, microscopic pieces of the metal valve get stuck in the pores of the grinding stone. This is called "loading."
When a wheel is loaded, it doesn't cut the metal; it rubs against it. This creates heat and friction, causing the valve to bounce off the wheel.
The Fix: You need to "Dress" the wheel. Dressing means using a diamond tool to cut away the top layer of the stone. This removes the stuck metal and reveals fresh, sharp grit underneath. Think of it like sharpening a pencil. If you want a smooth finish, you should dress your wheel often.
Grinding creates a lot of heat. If the valve gets too hot, the metal softens and smears instead of cutting cleanly. This looks like a cloudy or scratched finish.
The Fix: Check your oil! Make sure your grinding oil is flowing directly onto the spot where the wheel touches the valve. The oil washes away the metal dust (swarf) and keeps the valve cool. If your oil is dirty or the pump is weak, your finish will suffer.
Imagine holding a pencil by the eraser and trying to write. The tip wobbles, right? But if you hold it near the tip, it is steady.
The same rule applies to holding a valve in the machine. If the valve sticks out too far from the chuck, it will flex and wobble when the grinding wheel touches it.
The Fix: Keep it tight. Adjust your machine so the chuck grips the valve as close to the grinding face as possible, while still leaving room for the stone. The less metal hanging out, the steadier the grind.
This is the hard truth about equipment. Grinding is a violent process. It involves a stone spinning at high speeds crashing into hardened steel. This creates natural vibration.
Cheap, lightweight machines vibrate a lot. That vibration travels right into the valve, creating those chatter marks.
The Fix: Heavy-duty castings. This is why professional shops prefer machines like the SVSII Deluxe. It is built with a heavy cast-iron base. That extra weight absorbs the vibration so it doesn't reach the valve. It’s the difference between driving a luxury car over a bump versus a go-kart—the weight makes the ride smooth.
Even with a perfect setup, you can improve your finish with one simple trick. When you are finished grinding, stop moving the wheel forward (infeed). Just let it spin against the valve for a few seconds without adding pressure until the sparks stop flying. This is called a "spark-out," and it polishes the surface one last time.