The Sheet Metal Shop .Com :: View topic - Straight Offset vs. Mitered Offset

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Duct Construction and Uses - Straight Offset vs. Mitered Offset

Shon - Aug 10, 2006 - 04:25 PM
Post subject: Straight Offset vs. Mitered Offset

Hopefully this is the right forum.

Which is better? I've heard both sides....

Mitered is better because the actual dimension doesn't change.

Mitered is not better because it increases the actual offset in a shorter distance.

Any thoughts?

Shon

bordontn - Aug 11, 2006 - 02:17 AM
Post subject: mitered offset versus straight sided offset

I believe this is what Shon is refering to..see attached drawing..
8" offset on a 12" duct within 16" Drawn both ways. I think I would prefer
the mitered offset..Not an expert speaking,tho.......
"smart too late; old too soon"
bordontn

Doublecut - Aug 11, 2006 - 03:36 AM
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I prefer the mitered offset as well. If i remember correctly anything offseting more than 15 degree should be mitered or if one wants to do one better go with a radius offset.

Shon - Aug 11, 2006 - 12:21 PM
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bordontn nailed it with that drawing. Is there anyway to calculate the CFM that can be moved through each offset, according to the degree of the angle?

Just food for thought.

Shon

vezfriend - Feb 26, 2008 - 04:19 AM
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hey buds, i'd like to know more or learn a lot regarding mathematical solution involving air duct fabrication. In my country there are no graphic calculator so far issued or on sales for consumption, I used my old scientific calculator that took me almost an hour to do a layout of one fitting( regardless of size & metal thickness). Would you or is there someone who could help me or teach do a little mathematical solutions on solving my problems regarding sheet metal layout. Idea

LeadHead - Feb 29, 2008 - 11:02 AM
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I don't have one of these but, try this. http://www.sheetmetallayoutcalculator.com/

MattM - Feb 29, 2008 - 02:57 PM
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In the bottom drawing the cross-section area drops a considerable amount off its original size. (See his 10-3/8ths measurement?) The actual restriction is also a factor of length.

bordontn2 - Mar 03, 2008 - 02:00 AM
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MattM...That top drawing...You could probably add 35-45 ft.in duct length. 12x12 @ .08 would be 800cfm/850fpm
The lower drawing @ .08 would be 800cfm/950fpm at that point..still have to add 35-45ft.for the offset restriction....
Sumpin like that. A longer radius offset would only add about 10 ft. to your total length.........a radius 45° is worth 5 ft.
bordontn2