Tips for cutting straight lines in thin glass?

I've recently sourced some very thin (1.2mm) glass to use for dry plates and am finding it terribly difficult to cut reliably. I started off using the method that had been working well for thicker 2.4mm window glass, i.e. score with a rotary wheel cutter against a straight edge and then give it a firm whack on a flat surface to break along the cut, but this completely shatters the thinner stuff.

I then switched to a diamond scribe tool and align the score line between two straight edges clamped to the glass suspended over a dowel to which I then apply gentle pressure. This works well enough for short cuts, but anything longer than a few inches still breaks unpredictably at the edges and I end up having to trash the piece anyway.

Is there a foolproof method for cutting this stuff that I'm missing?

Get that scribe sound all across the glass and snap it apart by hand instead of whacking it.

It might be worth contacting a specialist glass cutting shop to see what it recommends? 1.2mm is incredibly slim and so easily shattered as you have found

pentaxuser

A glass cutter told me that glass goes brittle with age.
Cutting new glass for him was easy, but when a customer brought in their own, old glass to cut up for a new project it quite often led to failure.
Old glass seemed to have a mind of it's own, and a nice straight crack would veer off in an arc.
As pentaxuser said, a specialist may be the answer.

pentaxuser said:

It might be worth contacting a specialist glass cutting shop to see what it recommends? 1.2mm is incredibly slim and so easily shattered as you have found

pentaxuser

Click to expand...

1.2mm is about the same thickness as the glass I use for dry plates. I’ve cut thousands of sheets. Glass-cutting is a technique that requires practice, but once mastered is like riding a bike.

Scribe it right and then break it apart with your hands. Tapping it never works well. The key to proper scribing is listening for the sound. The scribe sound is a zip sound, not the crunching sound from pressing too hard, and not the sliding sound from pressing too soft.

My guess if you’re not breaking along the scribe is that you need to press harder or more consistently.

Once cut, it’s worthwhile to swipe the edges with a sharpening stone to knock that sharp edge down.

Tapping is an exercise in frustration, but I once managed to cut a "+" shaped piece of glass-- with 4 right angles-- by very careful tapping. I did it for a bet.

Stained glass supply shops (or Amazon) should have what are called "running pliers", which are pliers with a lateral curve at the grippy end, and usually rubber pads.

The scriber is also pretty important-- My mother made stained glass professionally, a long, long time ago, and there is a massive difference between the glass cutter you get at Ace Hardware, and a glass cutter designed for professional work.

Hers had a carbide wheel, and was oil filled. As you press down (gently) on the glass, a little bit of oil drips onto the wheel. The wheel is also very sharp, and takes less pressure. The difference in using that vs a "normal" glass cutter was like using a Brownie vs a Rolleiflex. Hers was very much like this one (in fact, it might have been a Toyo):

https://www.amazon.com/Toyo-Brass-Pencil-Style-Cutter/dp/B0149KLKYQ

And FYI, Jason, with the volume you cut, you might consider a stained glass grinder to smooth down the edges.

grat said:

And FYI, Jason, with the volume you cut, you might consider a stained glass grinder to smooth down the edges.

Click to expand...

The stock sizes are precut, swiped, and notched at the glass factory before being shipped to me. Custom sizes get swiped on a sharpening stone a stack at a time. Edging each plate individually would take too long.

Stained glass grinder and a bit makes the notch, stack at a time.

We use a benchtop cutter on a rail, kinda like the beetle bits cutting system.

Nodda Duma said:

Stained glass grinder and a bit makes the notch, stack at a time.

Click to expand...

You cut a stack of your thin glass in one go?

I think that's only cutting the notch to identify the emulsion side. Stack the plates and grind a vertical notch in the stack edge.

Correct, thanks Donald. My thoughts sometimes do not connect directly to my spoken (typed in this case) words.

Nodda Duma said:

The stock sizes are precut, swiped, and notched at the glass factory before being shipped to me. Custom sizes get swiped on a sharpening stone a stack at a time. Edging each plate individually would take too long.

Stained glass grinder and a bit makes the notch, stack at a time.

Click to expand...

Fair enough. I know the grinder my mother used could handle 3 or four pieces stacked, and it was typically "zip" each side. But it sounds like you're set up for similar speed.

We use a benchtop cutter on a rail, kinda like the beetle bits cutting system.

Click to expand...

Definitely worth it for huge amounts of straight lines.

Nodda Duma said:

Scribe it right and then break it apart with your hands. Tapping it never works well. The key to proper scribing is listening for the sound. The scribe sound is a zip sound, not the crunching sound from pressing too hard, and not the sliding sound from pressing too soft.

Click to expand...

Thanks Jason. This helped a lot. If I go very slow and listen to the scribe rather than watch it, I can bump my successful cut rate up to ~30% from ~5-10% which is nothing to sneeze at. I suspect I'll be able to improve a bit more with practice and a lot more sacrificed glass. Suffice it to say, this isn't the part of the dry plate process I thought would be consuming most of my time and anxiety.

The main difficulty seems to be that I'm 3D-printing my plate holders which requires a tighter tolerance than I may be able to achieve with hand cutting. I have half a mind to buy one of those cheap Chinese CNC laser engraver/cutters to see if it would have any success on thin glass. In the meantime I've also put in some RFQ's to glass manufacturers about minimum order sizes, because I'd much rather spend my time troubleshooting completely unrelated problems.

What about modifying a roller cutter, or even better making a similar stiff bridge from scratch, where you precisely can adjust the pressure of a scribe?