Strange chip/crack formation after drilling..thoughts?

[cambo123]

I have drilled tanks several times and never seen anything like this. Usually I create a damn with plumbers putty, set the drill to medium/high and let the drill pressure do its work. I always tape on the back side to prevent chip out.

See attached pic 1 of results. It clearly looks like a chip to me (pic 1), but looking from the back it has a clamshell formation that seems to be going into the tank (pic 2) beyond the chip in the front (crack?). Looking at the front you can then see two lines protruding a couple mm into the tank.

My inclination was to leave it be but I ended up using a diamond dremel to "cut/grind" it out pic 3. At this point, the black segment protruding out in pic two has been completely removed plus 1/2mm. I am not seeing any cracks looking up close. I am curious if anyone has seen anything like this before? Was my process appropriate for resolving this?

FYI this is for a eshopps overflow so its a 60mm hole with gaskets on both side. Glass is 8mms thick I think.

 

[lapin]

I think you did a great job. From the pictures it looks like you could have left it alone and it would not have been an issue.

 

[cambo123]

Thanks! Definitely a chip/crack I haven't seen before. Thanks for the feedback.

 

[der_wille_zur_macht]

I bet most people wouldn't have even noticed it. It looks like a normal harmless chip but I do see what looks like a feather crack as you're indicating. Probably fine to leave alone but your resolution was appropriate.