I've had no problem drilling lentils but you do need to make sure you have sufficient glass on either side of the mandrel. I've read at least 1- 1 1/2 times the amount of glass on either side as the thickness of the mandrel. And don't force the bead reamer. Let the grit do the job.
Also, did they break in half or just crumble into pieces. In half means thermal shock and they weren't evenly heated after pressing.
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ESC
Soft glass on a Minor/concentrator since 1996
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