Drilling glass for big bulkheads a few ?s

[jr999]

I've never drilled over an existing hole but using a 2x4 with a hole cut just bigger than the OD of the diamond bit helps me keep the bit from wandering. Do you have a piece of glass you could drill your holes sizes in as a test run.

[The Grizz]

+1 on the above, you need to center the bigger hole over the small hole and clamp it good. Lots of water & take your time it is a breeze.

[Hustler]

Ok ill give it a shot with a 2x4 and clamps... first i have to try and dig out the sump......damn center braces and plumbing.... need a sawzall just to budge it