can't cut bigger glass pieces

[neskusen]

I use a regular glass cutter with the carbide wheel to cut my glass sheets. It has always worked, cuts like through butter, just gently scratch it with the cutter then snap it into two pieces by forcing with hands.

But today I needed to cut a bugger shape, a triangle with 45cm sides, from a 3mm thick glass. I made the sratch as per usual, but no amount of pulling snaps the pieces. I then tried sratching again with a lot more force but it made no difference.

What do you think I might be doing wrong?

[turbohead]

I usually tap the glass on the other side of the score to start the controlled break.

[neskusen]

I did try tapping too (although I never needed to for smaller pieces) but I felt like if I try tapping any harder I'll just shatter the glass. I use the metal ball end of the cutter for tapping. But maybe I'm just tapping incorrectly or in the wrong place.
Where do you tap? On the score itself? Do you tap once or tap from one end to the other and break the glass segment by segment?
Or maybe the oil needs replacing.

[turbohead]

Tap directly on the opposite side of the score. Use very sharp taps. The glass should begin to show a crack through the glass along the score. Practice using a piece of scrap glass of the same thickness. I have successfully cut 1/4 plate this way. Do not re-score the glass. Also, apply some light oil on the score.

[neskusen]

I see, so you make several taps along the score. I'll try that.

But by sharp taps do you mean fast, or the object which is tapped with should be sharp?

[turbohead]

The taps (on the opposite side of the score) should be fast and short; an impulse type of hit. Use you wrist to make a sharp fast hit. Start rapping somewhere in the middle of the plate where you scored the glass. If you start rapping on the edge, the crack can start anywhere.

[Photonbeam]

Is it a piece of glass you have scored and broken before? If it is tempered glass you will never be able to score and break successfully. This happened to me with a 3mm thick IR filter from Edmund that I didn't know had a tempered glass substrate.

[buffo]

Tempered glass + scoring + tapping = explosion of glass fragments!

Once glass is tempered it can't ever be cut again - only shattered. (Also learned this the hard way.)

Adam

[Eidetic]

Did you continue the scribes beyond the triangle to the edge of the glass? It's important to let the cutting wheel fall off the trailing edge of the glass plate to get a good start to the break. It's also important to start the break on that trailing edge.

Is the glass AR coated? If so, the coating makes scribing much more difficult.

[neskusen]

It's a regular glass I bought from a shop, the cheapest one. Not AR coated or anything special. I needed the pieces to fit in my car so the large glass was cut into several 1m x 1m pieces.

I don't think its tempered, I accidentally broke one and it didn't shatter into million pieces, only few big fragments. Plus, I'm able to score and break the smaller pieces very easy.

Did you continue the scribes beyond the triangle to the edge of the glass?

yup

It's also important to start the break on that trailing edge.

I did not know this.
I will try again, after scoring I'll start to tap on the score from the end to the start of the score and see if cracks appear along the score.
Glad I got some extra pieces, 2 pieces are already destroyed.