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Old 09-27-2017, 09:14 AM   #1
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Gage metal required for a ceiling hatch

I am replacing an emergency hatch with a piece of sheet metal and attaching an exhaust fan that weighs @ 6 lbs. Would 22 gage sheet metal work for this application? I am not a metal expert and do not know if this is too thin.I tried for 10 gage but the fab shop does not have steel this thick.

Thanks for the input!

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Old 09-27-2017, 09:54 AM   #2
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Quote:
Originally Posted by chopanegas View Post
I am replacing an emergency hatch with a piece of sheet metal and attaching an exhaust fan that weighs @ 6 lbs. Would 22 gage sheet metal work for this application? I am not a metal expert and do not know if this is too thin.I tried for 10 gage but the fab shop does not have steel this thick.

Thanks for the input!
It's work, but is too thin. I'd go 16 Ga, but most here will tell you 18 Ga is fine.

10 Ga is a pita for small shops to work.

ga.gif
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Old 09-27-2017, 10:10 AM   #3
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I will second Rusty on 16 gauge metal. It does not seem to have the flex problems that 18 does, I replaced all the windows and covered the vents on my last bus with 16 gauge and there was no ripple in the metal. I riveted the patches into place on the roof and it was the strongest part since there were two layers Where they overlapped. Would be nice to have that added strength around the fan or AC. The roof on my Blue Bird would bow in when I stepped between the ribs.
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Old 09-27-2017, 10:54 AM   #4
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To put it in perspective, the escape hatch is probably about 20 inches square and the exhaust fan, if it's a standard RV type unit, probably is designed to fit a hole 14 inches square. That makes a 3 inch gap all the way around if the fan is centered in the larger hole.

If the inner hole is formed so that it has a lip rather than just a thin edge, a much thinner piece of sheet will suffice. Maybe as thin as 22 but really I'd go for 20 instead. Without the formed lip 18 or even 16 but certainly not any thicker than that.

If you have any interest in learning to form sheet metal this would be a great project to start. If my wild guess at dimensions above was correct, you could start with a piece of 20 gauge, cut it to 22 inches square, and cut an undersized opening in the center:
Click image for larger version

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Use something like a 12 inch adjustable wrench (basically, something with a deep jaw) to get the bend started along the inner dash-dot line. When you get into the corners you'll find that they don't want to go up. The metal needs to stretch there. It's not hard to do: just hit it. In a small-radius corner like this a small "hammer" will be needed. Even the handle end of the 12 inch wrench might be adequate. Alternate between stretching (hammering) and bending (with the wrench jaw) and soon there'll be a lip bent over to 90 degrees which will stiffen the part substantially. You'll get the hang of it. Even if you didn't... you'd probably be into it only two hours at the most, and that two by two foot piece of 20 gauge should cost no more than about $10 (maybe $60 to buy an entire 4x8 sheet).

edit: the above could be formed from 18 gauge too, but I'll tell you from experience, forming it in 16 gauge or thicker would be a LOT of work.
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Old 09-27-2017, 11:01 AM   #5
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Use something like a 12 inch adjustable wrench (basically, something with a deep jaw) to get the bend started along the inner dash-dot line.
Nice diagram- thanks for sharing !

These are nice investment for bending sheet for $25 link:

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Old 09-27-2017, 11:48 AM   #6
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I actually used the method described above to make openings for windows in my new body side panels last month. That metal was 18 gauge. I built a tool similar in concept to those HVAC seamer/duct-forming pliers, but at about 6 inches wide my tool took way too much force and I also couldn't get the tight bend radius I wanted. These HVAC pliers at 3-4 inches wide are narrower than what I built. They'll work great in 24 gauge and give diminishing results as the metal gets thicker.
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Old 09-27-2017, 12:10 PM   #7
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Quote:
Originally Posted by chopanegas View Post
I am replacing an emergency hatch with a piece of sheet metal and attaching an exhaust fan that weighs @ 6 lbs. Would 22 gage sheet metal work for this application? I am not a metal expert and do not know if this is too thin.I tried for 10 gage but the fab shop does not have steel this thick.

Thanks for the input!
I used 16ga, but 18 would work. Anything thinner would be too thin, imo.

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Old 09-27-2017, 01:00 PM   #8
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Thank you all for the great information!
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Old 09-27-2017, 01:03 PM   #9
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When you shop for a roof vent, I'd suggest the Fatastic brand, made by Dometic.
They're nice, have low current draw, and really do a great job. Maxxair are my 2nd choice.
The Heng's are ok, but better suited for cargo trailers and such.
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Old 09-27-2017, 10:09 PM   #10
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Great information, we are getting ready to do this on our skoolie.
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