Use the hot wire if your likely to use rods of 2"+. If the rods are 6" thick it doesn't matter either - you'd be best to use the hot wire. The crack may only be 10th" deep, however it's the disruptin to the surface that makes it easy to break the rod. The crack will easily run...
Found a "good book" relating to Fractography of glass - it covers flat, bottle and fibre glass - it contains plenty of pictures for reference - it is must for your library.
Details as follows - ISBN 0-306-44880-7
Fractography of Glass
by Richard C. Bradt & Richard E. Tressler...
If your only cutting an inch thick piece then three methods are at hand. 1- machine: diamond saws are available from places like Heathway or Jensons (UK), and I'm sure many others on the internet - this options is fast, accurate and neat. 2 - Thermal shock: use a glass knife or a metal file to...
The best material to use is fused silica - it's good from the far UV 180 nm upto 2500 nm. From 2600 to 2900 nm the transmission drops to about 10%. Then goes back to 90% +.<br>Quartz is OK but silica is better.