Formula didn't work (Conduit Bends)

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jddockery

Member
Normally, i would assume the take up of a bend is:

2*pi*radius of shoe*angle/360

the other day, a senior journeyman was bending a 30 degree bend on a shoe w/ 8.25" radius. Assuming correctly, the take up of the bend should have been approximately 4 & 1/4", he spaced the marking on 7", the second bend fell right on the first.............What happened? I would assume the shrinkage wasn't that much. Is the formula wrong?

Thanks in advance to any replies.

JD
 

celtic

Senior Member
Location
NJ
With an offset, you only need the multiplier for the angle.
The same multiplier will work on any bender, any size pipe, any type.

ie, a 14" offset using 30? bends.
Spacing between bends is 28"
Why?
The multiplier for 30? is x2 [14" x2 = 28"]
Pipe could be 1/2" - 4" EMT, IMC, RMC.


Try it on some scraps tom'row.
 

jeremysterling

Senior Member
Location
Austin, TX
First, I will admit that I do not use pi in any of my conduit bending formulas.

Secondly, you lost me when you said the J-man was bending a 30? bend and then the second bend fell on the first. What was the second bend for? An offset? What size offset?

Depending on pipe size, there are minimum offsets for the larger degree multipliers. For example, you will probably not be able to bend a 3" offset on 2" EMT using the 30? multiplier of 2. But you can certainly bend a 3" offset on 1/2" EMT using 30?.

Does this help?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
First, I will admit that I do not use pi in any of my conduit bending formulas.

Secondly, you lost me when you said the J-man was bending a 30? bend and then the second bend fell on the first. What was the second bend for? An offset? What size offset?

Depending on pipe size, there are minimum offsets for the larger degree multipliers. For example, you will probably not be able to bend a 3" offset on 2" EMT using the 30? multiplier of 2. But you can certainly bend a 3" offset on 1/2" EMT using 30?.

Does this help?

I agree with Jeremy, we need some more information regarding the type of bend. Bends overlapping on an offset means that the degree angle of bend was too large. And as Celtic stated typical offsets can be easily made by using multipliers.
 

jddockery

Member
Ok, to reiterate:

The pipe is a 2" pipe.

The angle is 30 degree's

This is an offset

The radius of the bender is 8.25

The formula for the distance for the perimeter of a circle is 2*pi*radius

30 degrees represents 1/12 of that, ergo (30/360) * 2 * pi * 8.25" = 4.32" should have been the length of the bend, & the second mark for the offset should have been free to make the offset,........unless i'm missing something.

using the co-secant of 30 degrees would have produced a 3.5" offset.

How does the width of the pipe play a role in your minimal spacing between bends. A mathematical explanation would be appreciated.

Thank you for your responses

Jd
 
Ok, to reiterate:

The pipe is a 2" pipe.

The angle is 30 degree's

This is an offset

The radius of the bender is 8.25

The formula for the distance for the perimeter of a circle is 2*pi*radius

30 degrees represents 1/12 of that, ergo (30/360) * 2 * pi * 8.25" = 4.32" should have been the length of the bend, & the second mark for the offset should have been free to make the offset,........unless i'm missing something.

using the co-secant of 30 degrees would have produced a 3.5" offset.

How does the width of the pipe play a role in your minimal spacing between bends. A mathematical explanation would be appreciated.

Thank you for your responses

Jd


I assume he just bending an offset. I cannot help you on this 'circle formula', but as others have said, depending on the depth/rise of the offset, for example, if you want a 10 inch rise over an obstacle, and you use 30 degree bends, the co secant multiplier is 2. basically multiply 2 X 10 = 20" , you would space your bend marks 20 inches apart and bend the pipe 30 degrees at those marks.
 

celtic

Senior Member
Location
NJ
Ok, to reiterate:

The pipe is a 2" pipe.

The angle is 30 degree's

This is an offset

The radius of the bender is 8.25

The formula for the distance for the perimeter of a circle is 2*pi*radius

30 degrees represents 1/12 of that, ergo (30/360) * 2 * pi * 8.25" = 4.32" should have been the length of the bend, & the second mark for the offset should have been free to make the offset,........unless i'm missing something.

using the co-secant of 30 degrees would have produced a 3.5" offset.


How does the width of the pipe play a role in your minimal spacing between bends. A mathematical explanation would be appreciated.

Thank you for your responses

Jd

To reiterate.....forget EVERYTHING marked in RED above....

That leaves us with:
The angle is 30 degree's

This is an offset

A mathematical explanation would be appreciated.
What is missing is the HEIGHT of the offset.

The size of the pipe you are bending is irrelevant.

The mathematical explanation is Pythagorean Theory.

offsets.htm_txt_OffsetTriangle.gif


offsets.htm_txt_Offset.gif


The diameter of the pipe does not play into the equation at all.


I could go on and on and cut/paste all the info.....


...but why?


Give the material at the Porcupine Press an eyeballing.
Conduit Bending
Stub Ups
Back To Back
Offsets
Saddles
Parallel Bends
Segment Bends
Concentric Bends


If you have any questions/comments AFTER reading the above......come on back ...we'll help you however we can.
 

quogueelectric

Senior Member
Location
new york
Normally, i would assume the take up of a bend is:

2*pi*radius of shoe*angle/360

the other day, a senior journeyman was bending a 30 degree bend on a shoe w/ 8.25" radius. Assuming correctly, the take up of the bend should have been approximately 4 & 1/4", he spaced the marking on 7", the second bend fell right on the first.............What happened? I would assume the shrinkage wasn't that much. Is the formula wrong?

Thanks in advance to any replies.

JD
The formula is never wrong. The operator frequently is though. Back to the drawing board for the j-man with excuses.
 

ohmhead

Senior Member
Location
ORLANDO FLA
Well pipe diameter does effect space when using a 555 or 881 bender pipe size to offset distance and the formulas will not work if your pipe diameter and shoe cant fit into the formula and you cant sqweezzzzz it out if you do not have the distance to bend it .


You dont need a formula for that just your eyes to see radi of shoe to distance between marks .

At 30 deg or 45 deg you can only get what you can but if you want to go to the next level bigger pipe think smaller deg longer markings to get same offset .

Most electricains use 30 deg and 45 deg because its easy to use try 5 deg 10 deg 15 deg this will help your pulling and you problem with your shoe to pipe size .
 
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