How to edge a curved mirror without breaking it: the tip that saved EP1

In the home stretch of Arena do Vidro EP1, Janael was already fitting the LED and Rômulo moved on to edging. It was the last heavy step before assembling the Hello Kitty mirror. And that's when I heard the line every glazier has said at least once: "I think it's going to break".

It didn't. And the reason deserves a whole post, because edging a curved mirror, especially an inside curve, is where a lot of good pieces end up in the scrap bin. Here's what happened and what the panel taught.

The chatter: "I thought it would break"

Rômulo explained afterward: he's used to edging one way, and there he had to make do with that machine. On the curve, the mirror started chattering. He said he really thought it would break, and it was close.

Chatter is the warning. When the mirror starts vibrating against the wheel, something is forcing the piece: speed, angle, pressure, or a defect on the edge that the wheel keeps hitting. Push through it and the vibration turns into a crack.

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Vinícius's tip: speed and tilt

Rômulo did what many people are too proud to do: he asked for help. Vinícius, with 30 years in the trade, gave him the technique on the spot. Lower the machine's speed a little and change the tilt. In Rômulo's words, that tip saved him, because otherwise he couldn't have finished.

It makes sense. On an inside curve, the mirror touches the wheel over a small area and the piece tends to "jump". With less speed, the machine runs smoother. With the right angle, the wheel follows the curve instead of slamming into it.

The chip that came from break-out

While Rômulo fought the machine, the panel spotted where part of the problem came from. He had a small chip on the edge and was struggling to work it out at the edger. That chip came from something Vinícius had mentioned early in the episode: tapping with the cutter to open the score. Had he used his hand, the light tap from below, nothing would have happened.

As one judge put it, it's a detail every glazier deals with in real life. A mistake in one step shows up in the next. Break out badly and you edge more, with more risk.

Inside curves: "you need the knack"

The panel was blunt: edging an organic-shaped mirror with inside curves takes knack. Without it, the glazier either breaks the mirror or can't get a proper finish. And the stakes were high: Rômulo was ahead, but if he broke the piece there, he'd lose it all.

• Clean break-out first: with no chip on the edge, edging goes smoothly. Tap from below, not with the cutter's ball.
• Slow down on the curve: that was the first half of Vinícius's tip.
• Adjust the tilt: the wheel should follow the curve, not hit it.
• If it chatters, stop: chatter is the warning before a crack.
• Light pressure and a steady pace: let the machine do the work.
• Ask for help: in EP1, one quick tip saved an hour and a half of work.

Steady beats rushed

There was a swing: Janael got ahead, Rômulo passed him, then Janael went back in front when Rômulo got stuck edging. Even so, the panel noted that Rômulo kept the same pace. He saw his rival closing in and didn't try to rush. He finished the piece, bow and all, and won the episode 7.5 to 6.

Why does a mirror chatter when edging a curve?

Because the piece is being forced against the wheel: speed too high, wrong angle, too much pressure, or an edge defect like a chip from break-out. In EP1, chatter nearly broke Rômulo's mirror.

What was Vinícius's tip for edging the curve?

Lower the machine's speed a little and adjust the tilt. Rômulo said that without that tip he couldn't have finished.

Does a break-out chip make edging harder?

Yes. In EP1, the chip made by tapping with the cutter made edging harder. According to the panel, a light tap from below by hand would have avoided it.

The clip with this part is at the top of the post, and the full EP1 is on the episode page. If you can edge an inside curve without flinching, applications for the next Arena season are open here on the site.

Full episode 1 · How to break out a mirror without chipping · How to edge a mirror without dust

Episode 1