The press is DK-3 and the mugs are from Novachrome USA (they say made in China on them but then again, everything here does)
I am suspecting 1 or a combination of 3 things.
1- the mug press is running hot. I have an instant read temp gauge so I will put it on the press when I start it back up
2- The mug is damaged and I didn't notice it
3- The mug is defective
Out of the first 49 there were 3 that cracked, one was broken when it came out of the box and the other had a big flaw in it.
I have been setting the mugs down, putting the next mug in and waiting about 20-30 seconds before putting it in the water. No cracks since then. I just don't want them cracking after delivery.