Drilling a bigger hole over an existing hole

[Pharaoh]

I have drilled tanks with and without the center guide but in place. I have also done it with a jig as well. It can be done without a jig, but it is difficult.

You can drill it with water in it, just make sure that you keep debris from falling in the tank or the fish will eat it.

 

[Reptile88]

do you have the hole saw that fits the existing hole? if so bolt that hole saw into the new size hole saw and now you have a pilot bit that fits the hole

 

[knobhill]

Sure, just keep a net handy to scoop up the tiny pieces that will fall into your tank. I've had to cut away parts of my top panel to reach fish stuck in my overflow, what i didnt get with the net the filter picked up..

Actually, the holes are on the bottom panel, kept dry from the overflow. I have drilled holes in the top of acrylic tanks filled but never from the bottom. Anyone done that? I know, strange situation.

 

[knobhill]

do you have the hole saw that fits the existing hole? if so bolt that hole saw into the new size hole saw and now you have a pilot bit that fits the hole

I think I do. Good Idea!

 

[knobhill]

I finally had the time to drill the holes and used two different methods.

#1: Used a hole saw that fit the existing hole and bolted that hole saw into the larger desired size hole saw. I changed a 1 7/16" to a 1 3/4" as well as a 1 3/4" to a 2 1/2".

The key to this was buying a hole saw set ($20 at Lowes) because each bit has the same hole to accept the pilot bit.

#2: This was a lot trickier. I changed a 2 3/8" hole to a 2 7/8" hole. It required more finesse because the hole was located on the bottom of the tank and couldn't be drilled with the first method because I needed the hole offset instead of centered on the old hole. I first measured 10 times where the offset, large hole needed to be...then I checked again. Next, I used the 2 7/8" hole saw to cut a hole in some scrap plywood. I clamped the piece of plywood against the stand, checked to see from the top of the tank that is was where I wanted it. The plywood acted as a guide to start the hole. After getting about 1/8" deep, I didn't need the plywood guide and finished the hole.

I hope this experience can help any members looking to upgrade their flow rates in their tanks.