Importance of fillet in 2.5 converted to rimless? - The Planted Tank Forum
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post #1 of 6 (permalink) Old 03-06-2010, 08:14 AM Thread Starter
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Importance of fillet in 2.5 converted to rimless?

Was reading that the shear strength of silicone holding the glass is very weak, and most of the strength is in the tensile strength. The fillets only rely on shear strength.

Was debating doing a rimless 2.5. On top of derimming, I was pondering removing the fillets, so that the only silicone is between the glass. Has anyone done this when removing the excess silicone?

Also, I see alot of converted rimless tanks, but not alot of mentions on whether or not the tops were razor sharp, or even or whatever. I can buff the sharp edges, but even with 60 grit it's pretty difficult to knock down glass, and I don't think a person at home would be able to even out the top panels with sanding... Can anyone who's derimmed comment on the quality/evenness of the top panes of glass on their tanks?

Lastly, how bad has the water evaporation been for you? I always run with a lid on my nano, so I'm not sure how much it would lose in 1 or 2 weeks (I plan on doing EI dosing anyways with associated 50% weekly water changes).
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post #2 of 6 (permalink) Old 03-06-2010, 09:25 AM
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The knock down glass use a sharpening stone used for knives. I used a nice hard stone that was 7 dollars.
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post #3 of 6 (permalink) Old 03-08-2010, 08:39 AM Thread Starter
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So I bought a new one from petsmart, and derimmed it. Just grinded down the top of the plastic rim with a dremel router bit. It doesn't hurt/scratch the glass on the edge. Rim came off in two pieces neatly.

Removing rim is easy, what I'm unsure of is the removal of the excess silicone. From the pictures I've seen it's hard to determine to what extent silicone was removed.

Since I read elsewhere that the fillet is essentially useless, I took a rectangular razor blade and removed all silicone except at the glass on glass joints. Unfortunately when they built this tank, apparently they did not put silicone over all the glass on glass portions, so the tank did leak.... I don't know if I could resilicone it just at the glass on glass joints with minimal squeeze out, and am debating just cleaning up the corners and adding another bead fillet.

Soooo, to all you derimmers, to what extent did you remove the excess silicone?
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post #4 of 6 (permalink) Old 03-08-2010, 08:28 PM
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I am also interested in this. Do you have any pix of your work so far yet? Sort of interested in how/where you actually dremeled? I might be interested in doing this to my 5gal as well.
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post #5 of 6 (permalink) Old 03-09-2010, 02:06 AM Thread Starter
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None of the other pictures came out well. I dremeled the highest part of the tank. It's the top most part of the black rim. Perhaps 1-2 mm deep into the plastic you will hit the glass. I tried a razor plane and a hobby knife and they were pretty useless on trying to shave down the plastic. The dremel router bit CAN cut the plastic, but it's far faster to just melt the plastic with it. I eventually just plunged the bit into the plastic until I hit glass, and then just pushed it along the plastic, melting as I went. I was afraid of overheating the glass and chipping/cracking it, but I had no problems. Once you have grinded down the plastic on the top and you can see all the top of the glass, there is a minimal amount of silicone to slice through at the corners and then gently lift the rim off the glass. It required minimal force to remove it... I think with a tank this small, you'd likely shatter the glass with the force required to use a block plane..

Trick to removing the corner silicone is to use a rectangular razor blade instead of the more common trapezoid shaped ones. This allows you to use the side of the blade as a guide and prevents you from accidentally going into the silicone at the glass-on-glass joints. Unfortunately it does not seem that the manufacturer of my tank intended to put any silicone at the glass on glass joints and instead relied on the fillets. After further cleanup of removing the fillets, the panels all just came apart and I can only detect silicone in a few places.

I'm kind of frustrated. If I'm going to go through all the trouble of resiliconing it, I might as well try to get the 5mm glass that the ADA tanks use. Glass companies want at least $50 for that amount of glass unfortunately. Home depot/Lowes only carries 2.4 mm glass. Ace hardware has 3.2 mm glass at reasonable prices and will cut it. I was convinced my tank was 2.4mm glass, so I bought the 3.2 mm glass, and it turns out that everything is 3.2 mm. Using a rimless tank calculator with a 3.8 safety factor, the sides have to be 2 mm and the bottom has to be 3mm, so 5mm glass isn't necessary.

I'd still like to know how others are handling their silicone.
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post #6 of 6 (permalink) Old 03-11-2010, 02:01 AM
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I personally would not have cut the silicone out. Silicone is a sealant, not a bonding agent. Most tank manufacturers do not "glue" the panes together with silicone. It is just used to seal the tank so it does not leak.

And since you removed the rim that held the glass in place, I would never feel safe without the silicone fully in place. IME small tanks like this will work just fine without the top rim, but I believe that leaving the silicone in place is a fairly traditional safegard when de-rimming a tank.
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