1. ## O.W.L. Method

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Like what it means offset*width/length u basically are just mitering the duct for an offset all it is is a formula if u have duct 20 width 5 ft long and need an offset of 2 20*2=40/5=4 inches taken off all sides also depends on if your offset is off the width or height side it's tricky at first but takes alot of practice and craftsmanship

3. Originally Posted by silkysean
Like what it means offset*width/length u basically are just mitering the duct for an offset all it is is a formula if u have duct 20 width 5 ft long and need an offset of 2 20*2=40/5=4 inches taken off all sides also depends on if your offset is off the width or height side it's tricky at first but takes alot of practice and craftsmanship
I know what it means..But really I want to know its limites..I think the max off set you can make is 7"..Is this true as far as you know?.. Thanks..

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yes and no as i stated a lot of factors determine this it all depends on length and width this truly dictactes offset for formula

5. Originally Posted by silkysean
Like what it means offset*width/length u basically are just mitering the duct for an offset all it is is a formula if u have duct 20 width 5 ft long and need an offset of 2 20*2=40/5=4 inches taken off all sides also depends on if your offset is off the width or height side it's tricky at first but takes alot of practice and craftsmanship
That formula would actually be (20*2) / 60. You need to plug all your numbers into the formula with the same increments, whether it's inches, centimeters, etc.

The "owl" method has it's faults that I've found. The larger the numbers are, the less accurate it is.

I've done some pretty steep and long compound offsets using multiple joints of ductwork with a straightedge, tape measure, and sharpie. Most have been accurate to within a 1/4", so I'll stick with that.

Sean is right about one thing... A couple different factors go into deciding how large of an offset you can make... The joining medium being one of them. If you get TDF more than 1/4" - 1/2" misaligned, you'll never be able to cleat the odd side. With lighter gauge metals and slip/drive, you have a greater margin for error, but there are still limits. The steeper the offset is, the more the joint will grow out of it's original dimension.
Last edited by Tech Rob; 12-31-2007 at 01:43 AM.

6. Get yourself one of these and you can cut 30" offsets into a 5' joint of 60/40 all day long

You can even miter the adjacent side and make a really clean looking compound, joined with whatever you like

7. I sometimes use the SWAG method.....Scientific Wild A\$\$ Guess

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Does it possibly refer to Offset Wrapper Length when calculating the wrappers for an ogee offset? If so I calculate them using this formula (slant length-working length)divided by 3 then multiplied by 4 plus the working length and allowances for connectors. maybe this isn't what it refers to but that would be my guess??

9. OWL. Offset times width divided by length, works every time.

10. ## offsets

Offsets , I've made a few. Here's what I know ...

The " shortest possible " ( length without choking ) I did like this ...

1) layout the cheek dimension on the metal edge closest to you ( allow for seams ).

2) Scribe an arch ( direction of offset ) of that dimension to at least 90 degree.

3) Sqare a line from the bottom ( representing the offset dimension ) to intersect the curved line drawn in 2 to establish point" c ? ".

4 ) With C as center scribe a line tangent to the curve drawn in 2. Square the lines to establish the rest of the layout. Or leave the curved lines and fabricate the fitting as a curved " barrell offset ".

This is used for an offset that is to be " as short as possible " ...but can be stretched to make a nice angled offset or barrell type offset fitting. Low presure and velocity applications only on this one.

The term " ogee " was refered to in old layout and drafting text indicating a " compound curve "...such as a curved fitting offsetting 2 ways ( with both patterns curving in transition ) ( or an old speaker from a record player ...RCA dog ). A standard curved offset is now refered to as " ogee " ...so , whatever. A simple curved offset is not " compound curved " but rather a paralell straight patern that can use a Pittsburg seam on it's wrapper ( a two way offsetting fitting an angled flat pattern ) .

A simple curved offset ( heel and throat ) is as not difficult to layout as it is to type instruction ( with no illistration ). There are many books out there that can explain this better than I can and I recommend them all ( Richard Budzik and Joseph Kaberlein ).

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