take offs

[BootsyHandy]

how to calculate 45 and 90 elbows

[William McCormick]

Are you talking about square, round, one piece, or multiple gore elbows?

Sincerely,

William McCormick

[William McCormick]

This is what we call a three gore elbow, it actually has two full gores and two half gores, however it seems to be a more sane stronger design. It is the norm now when talking three gore elbows.

It really is easier than it looks to lay this out. You do have to add over lap if you are dealing with sheet metal and you are going to rivet or press form bond them.



Square elbows are super simple.

Sincerely,

William McCormick

[hommeacier]

how to calculate 45 and 90 elbows

Since there is little to calculate on rectangular and square elbows,I'll assume that you mean ROUND elbows.

When calculating round gored elbows,here is the rule to remember; the number of pieces(gores) x 2 -2. Divide this into the degrees of the elbow. This will give you the degrees for your end gores.Example:For a 4 piece 45 deg. elbow, 4x2=8. 8-2=6. 45 divided by 6=7.5 degrees.Two of these end gores and two full gores at 15 degrees each equals 45 degrees.
>In short form: Deg./(no.pcs.x2)-2. This formula works for any degree elbow with any number of pieces. Then proceed as William McCormick showed.

[William McCormick]

Good point, I believe most people never start because they do not know where to start. Or they are missing information. Most of the time for an elbows inside radius we just make it half the diameter of the pipe. This has worked well for us.

I have seen guys that have hammered duct together for years not know where to start when making a square duct elbow. Things like the throat, what depth, should it be square or have a radius? This has caused them to get stopped. Should it have an outside radius or turning veins? Half the problem is not knowing what they want to build rather than worrying about how to build it and fifty other types of duct. I have found once I have an actual task I will find out how to make it if I do not know.

If it is not a welded round or square duct, allowances have to be made for a pittsburg or ACME seam, often these allowances work in an opposite way the mind normally thinks. So again they never get started.



In the shop if I am making some elbows I make a 30 degree pie slice, by using dividers (a bar compass) for lack of a better description. I make a circle and then create an arc with the pivot point at the lower quadrant of the circle. I start the arc from the center of the circle to the edge of the circle and well beyond. The radius of the arc is the circle radius. And then where the arc intersects the circle I make that the pivot point and I just swing another arc through the center of the circle and outside the circle to where the two arcs intersect. That intersection point the center of the circle and the lower quadrant of the circle point create a 30 degree angle.

Looking at the picture I attached, you basically draw a line A,B then draw a circle with its center C, on A,B. Put your dividers on B and swing an arc from C to H and well beyond because you do not know where H is yet. Then put your dividers on G and swing an arc from C to H and where they intersect is 30 degrees. B,C,H creates a 30 degree angle. You can also cut one in half to make 15 degrees too.

B,C,G is 60 degrees.

Good thinking.

Sincerely,

William McCormick

[William McCormick]

I usually know the number of joints ahead of time. So if it is a ninety degree elbow, I just divide by the number of joints. If there are three joints I divide 90 by 3 making each joint a 30 degree angle. So each piece at a joint is on a 15 degree angle.

If it was a 45 degree elbow each joint would be 15 degrees and each piece at the joint would be half of that 15 degrees or 7.5 degrees.

Sincerely,

William McCormick

[TimmyTIG]

On a 90, multiply your pipe size by 1.5. 6 inch 90 takeoff = 9 inches............. 12 inch = 18 inches, etc.

On a 45, divide your pipe size by 2, three times.

6,3,1-1/2,3/4.

then add the second and last numbers. 6 inch 45 takeoff = 3-3/4"

12 inch - 12, 6, 3, 1-1/2..... 12 inch 45 takeoff = 6-1/2"

I believe you can also multiply pipe size by 5/9 to get a 45 takeoff

[rtlflat]

Dividing by 2, three times....
=Just divide it by 8..... Why does everybody always say 2, three times?

[William McCormick]

In real life or on big jobs the office would not allow us to make four piece elbows if they are only 45 degree elbows.

They would take out a full gore for sure. On big jobs they just program it into the plasma table so there is no calculating. I have even done jobs where they just programmed and cut pipe so the ends of the pipe are on an angle and that was it. I just supplied them with the angle I needed. What ever angle five feet of pipe would allow to get us tight to a large round wall. Five feet is because it is the maximum length we could get into the roller.

Sincerely,

William McCormick

[William McCormick]

On a 90, multiply your pipe size by 1.5. 6 inch 90 takeoff = 9 inches............. 12 inch = 18 inches, etc.

On a 45, divide your pipe size by 2, three times.

6,3,1-1/2,3/4.

then add the second and last numbers. 6 inch 45 takeoff = 3-3/4"

12 inch - 12, 6, 3, 1-1/2..... 12 inch 45 takeoff = 6-1/2"

I believe you can also multiply pipe size by 5/9 to get a 45 takeoff

What application are you making them for? That would be a nice elbow you are describing, but nowadays there is just no room for it in most HVAC jobs I see.

Sincerely,

William McCormick

[92dlxman]

butt weld 45's are either the 1/2 of diameter 4 times and taking 2nd and last or 5/8 the pipe size, as said above. handy to know the 5/8 trick when working on a calculator. (.625 x 6 = 3.75)
as with 6", you would say 6, 3, 1-1/2, and 3/4, so you are whole, half, quarter, and one eighth the original diameter. taking the proven 2nd and last number added together means the takeoff is 1/2+1/8 the original diameter, which is 5/8. 5/8 of ("of" is a short way to say "multiplied by" but if you say "out of" think division) 6 = 3-3/4

i have found pipe 3" and under to not follow the rules. i have to look those up to get perfect fit. i know a 3" 45 is a 2" takeoff. weird.

90's are, as stated above, 1.5 diameters. in sch pipe, that is long radius, and is common. short radius is 1 diameter. tubing (like process tube or conduit) can get odd cause they have huge radius elbows, or elbows with strait tails on them that can make fitting difficult if the guy ordering didn't tell you what he bought.

[TimmyTIG]

What application are you making them for? That would be a nice elbow you are describing, but nowadays there is just no room for it in most HVAC jobs I see.

Sincerely,

William McCormick

This is for piping systems, refineries and power plants, etc. Forged fittings, not hand made. The fitting takeoff is used for finding piping cut lengths on isometric drawings that usually just give you center to center dimensions.

So, for example: You have an iso drawing that you have to build, it shows a a run of 6 inch pipe with 90s on each end, and gives you a dimension of 6 feet from center of 90 to center of 90. You takeoff for two 90s, 9"+9" =18" - and that gives you a cut length for your pipe of 4'6".

[TimmyTIG]

Dividing by 2, three times....
=Just divide it by 8..... Why does everybody always say 2, three times?

Because you have to add the second and last numbers.
6 divided by 8 does not equal 3-3/4.

[92dlxman]

but six divided by 8 would be 1/8 of 6 which is .75, added to half of six (totaling 5/8 of six) = 3.75

[TimmyTIG]

so you would have to say: x/8 + x/2 = 2 much algebra for this old welder.

[TimmyTIG]

butt weld 45's are either the 1/2 of diameter 4 times and taking 2nd and last or 5/8 the pipe size, as said above. handy to know the 5/8 trick when working on a calculator. (.625 x 6 = 3.75)
as with 6", you would say 6, 3, 1-1/2, and 3/4, so you are whole, half, quarter, and one eighth the original diameter. taking the proven 2nd and last number added together means the takeoff is 1/2+1/8 the original diameter, which is 5/8. 5/8 of ("of" is a short way to say "multiplied by" but if you say "out of" think division) 6 = 3-3/4

i have found pipe 3" and under to not follow the rules. i have to look those up to get perfect fit. i know a 3" 45 is a 2" takeoff. weird.

90's are, as stated above, 1.5 diameters. in sch pipe, that is long radius, and is common. short radius is 1 diameter. tubing (like process tube or conduit) can get odd cause they have huge radius elbows, or elbows with strait tails on them that can make fitting difficult if the guy ordering didn't tell you what he bought.

This is true. The formula doesn't work for small pipe. Best to just have a Blue Book and have them memorized.

[rtlflat]

6 divided by 8 does not equal 3-3/4.

It does if your a pipefitter

[TimmyTIG]

It does if your a pipefitter

Care to show your work, Mr. Pipefitter?

[TimmyTIG]

I've worked with some pipefitters that couldn't spell pipe, much less fit it.

[William McCormick]

This is for piping systems, refineries and power plants, etc. Forged fittings, not hand made. The fitting takeoff is used for finding piping cut lengths on isometric drawings that usually just give you center to center dimensions.

So, for example: You have an iso drawing that you have to build, it shows a a run of 6 inch pipe with 90s on each end, and gives you a dimension of 6 feet from center of 90 to center of 90. You takeoff for two 90s, 9"+9" =18" - and that gives you a cut length for your pipe of 4'6".

I get you, good to know. Thanks

Sincerely,

William Mccormick

[rtlflat]

Care to show your work, Mr. Pipefitter?

I'm only a second year apprentice sir. Just gimme three more years and I'll be ready