my glass saftey test gone bad

[spamreefnew]

ok so i had 2 old cracked 10 gallon tanks that i was about to toss in the garbage ,when i thought to my self "why not practice drilling on them? so i did. the rear panels of the tanks each had small crack in them but the fronts and sides wear in great condition. so i made about a 1/4 inch hole on the left side of each to simulate an overflow hole. the holes cut e/z and are nice and clean looking with no chips or hairline cracks what so ever. so now for the strength test... i put on some rubber gloves and placed my hand in tank one and bumped it around to simulate cleaning the glass or moving equipment,,,,guess what....it cracked right where the hole was drilled! so on the next tank i avoided the drilled area and no cracking..so then i whaled on an area away from the hole...and still no cracks....then i lightly bumped the area with the hole and it split right open. this test is making me think that drilling a tank can weaken a tank to the point where it is dangerous! has anyone run into this? i was planning on buying some 10 and 20 gallon tanks for my new sump room but now i am scared to drill-out $200 worth of tanks just to have them crack when i tighten bulkeds or clean them:eek:

[oldsaltman]

The problem is those are small tanks with "thin" glass, and it cracks very easy. I just drilled eleven holes in the back of my new 90g and it is now full of water with no leaks. The difference is that it has "thick" glass. :smokin:

[spamreefnew]

i just cant help but wonder if you glass is now only as strong as lets say 1/8" un-drilled glass now?

[spamreefnew]

as i said ,i was able to realy bash on the un-drilled portion of the little 10 gallon tank without it breaking.

[The0wn4g3]

It broke because, as oldsaltman said, 10 gallon tanks have very thin glass compared to any other tank. You could go to a local glass shop and get your hands on a scrap piece of 1/4" glass and re-do your test. It shouldn't crack, and if it does, there is something wrong with the glass :)

[gilweb]

Once you install a bulkhead, wont it help to strengthen the glass where there hole is?

[NanoReefWanabe]

before you start bashing the glass around...put a bulkhead in the hole you drill....obviously the glass will be weaker once the hole is drilled in it...the bulkhead will help strengthen up the hole...

and yeah that 3mil glass used in 10g tanks is fairly thin....it is kinda like old fashion window pane glass...

20g tanks are 5mil glass and quite a bit stronger then the 10's...

[das75]

this was with a diamond hole saw?

[Agu]

I have drilled ten gallon that's been running for four years without a problem.

The biggest problem I've run into in the Nano forum is when people use wrenches to tighten the bulkheads and put sideways pressure on the glass.

[8BALL_99]

For the most part 10 gallons are just to thin to drill. I've drilled several for other people and all of them ended up cracked sooner or later. I won't even drill them now. Ofcourse if you drill holes in something it makes it weaker :)

[dots]

Remember glass is a brittle material, and will only withstand a small amount of deformation before it fails.

Stress is the Engineering property that is expressed in units of Force/Area.

At a known value of Stress, glass will fail along the weak points in its crystal matrix.

So consider a force running in one direction across the surface plane of the glass, because it is a uniform piece the load is equally distributed. It is because of this, the Stress doesn't exceed its maximum, and remains intact. Picture the force running across like an infinite amount of freeways running across. Traffic flows nice and uniform.

Drill a few holes now, one on top of the other spaced a small distance apart. Just like an obtacle on the freeway, the force must squeeze through a smaller "area" in between the holes. The stress is concentrated here, and exceeds to cause failure.

In addition, cold working material introduced localized stresses and sharp corners, edges create opportunity for crack propagation to begin.

All of this is oversimplified and exampled in a single direction, static load. However, life is very dynamic so there are multidirectional forces of varying magnitude being imparted on the material. All of this can be difficult to predict the results of and where detailed calculations were made in the past, and nowadays accurate CAD models to be used to simulate the forces and their reactions throughout the structure. Examples of these combined forces are the localized compressive force on the glass if the bulkheads are overtighted, or if it is used as a moment arm (torque arm) when connections are made.

The old design rule of thumb is space the holes from the edge of the material or hole edges, no less than 1.5X the diameter of the hole to be drilled. This is a minimum value and more is often recommended.

At a certain point, there is nothing but swiss cheese and you can take away too much of the glass.

I hope this helps you better understand what you are seeing.

[laverda]

A lot also depends on how close to the edge of the glass you drilled your hole. Chips also weaken it substantially.