How to cut a tank without cracking?

[Michael L.]

I'm currently working on building a 2.5 gallon tank with 2.5 gallon sump, but I've never worked with glass before and I'm just getting used to my rotary tool since I just got it. I built an external overflow today using some scrap glass and my "Jobmate" rotary tool (like a dremel). I'm using both Dremel brand "Diamond Point" and Dremel brand "Diamond Wheel".

I think my rotary tool is rated for 33,000 RPM, but the speed dial goes from 1-5. I'm doing around 3 because anything above that turns the accessory red from the friction. What RPM would you recommend for these accessories?

Today, I had no problems cutting pieces of glass to make my overflow box, but when I went for the black plastic trim at the top of the tank with the Diamond Wheel to make some "teeth" for the overflow, the tank immediately cracked. I know it isn't tempered because of the way it cracked, but I can't figure out what went wrong, and I don't want to waste another $10 on a tank I'm going to break.

I was cooling it with syringes filled with cold water by the way.

Does anyone have any tips so i don't break any more tanks?

[jkta99]

you could use plexy glass instead of glass for the overflow.

[Michael L.]

What do you mean? Replace the rear wall with a piece of plexi? I could do that, but I heard plexi swells with water and can break the glass.

[jkta99]

So are you placing the overflow on the outside of the tank, sorry I am confused as to how this is being set up.

[jkta99]

this might give you some ideas

http://reefcentral.com/forums/showthread.php?s=&threadid=1120682&highlight=cutting+teeth+for+overflow

[Michael L.]

I'm doing what Mr. Spiffy described in the first post. The trim on most of the back of the tank will be cut off and an overflow box will be placed on the outside. So I guess I won't need teeth?

[jstraka1]

It souds like you need more water for cooling. You should be able to run at the highest speed and not get red hot. Fill a gallon jug with water and run a siphon of airline tubing with a small valve and drip water on it while you are cutting. This might help.

[storrisch]

I have actually done this exact idea. I cut it in the bathtub with new water flowing on it nonstop (of course not enough to end up electrocuting myself...ps only use a GFCI outlet w/ the dremel and water just to be safe.) The internal overflow was actually cut from a cracked 5gal I picked up from someone.

I would not try cutting the plastic bracing on the tank. The glass is so thin that if the dremel grabs the plastic at all it is gonna crack the glass every time. When I cut I use the dremel on the 3rd slowest setting.

Hope this helps. I've added some pics from my build that still looks the same after 8 months. I need to get around to building a stand for it.

http://i109.photobucket.com/albums/n59/storrisch/overflowsilicone.jpg
http://i109.photobucket.com/albums/n59/storrisch/overflow.jpg
http://i109.photobucket.com/albums/n59/storrisch/DSCF2691.jpg
http://i109.photobucket.com/albums/n59/storrisch/bottombulkhead.jpg
http://i109.photobucket.com/albums/n59/storrisch/drilledbottom.jpg
http://i109.photobucket.com/albums/n59/storrisch/tankshot2.jpg

[Michael L.]

So I can't cut the bracing? Once the tank cracked, I figured, why not, and I tore off the bracing with my hands. I know it is possible to do if you are very careful, and I have to do it it for this project. I think what I'll do is just cut the bracing where I want to remove it, and tear up the strip with my hands, then I'll just leave the overflow without a screen.

[Michael L.]

Success! I used the Dremel Diamond Point to cut along the bottom of the trim and then I cut upwards through the trim. Now I'm just waiting for the Krylon paint to dry so I can silicone on the overflow.