Calculations for Conduit Bending

[2Broke2Sleep]

I am trying to wrap my head around how the multiplier values are created for the push thru method of bending conduit.

For example: In a 3 bend saddle with 45 degree center, your multiplier is 2.5 for the standard method but 2.61 for the push thru method. Further, the conduit O.D. is added to the quotient of the offset height and multiplier with the push-thru. This leads one to realize the distance from center to outer bends is 1/2 x the O.D. shorter on each side when utilizing the push-thru. That's where I get lost. Since the bender faces the same direction throughout that seems to be the factor that changes the math.... You are advised to make center of bend marks for your outside bends as well, which could also be a factor in determing the outside marks......

Not going to change the quality of work enough to matter but it irks me enough to not stop thinking about it....

 

[Smart $]

Push-through method means maintaining conduit orientation for all three bends versus the standard method in which you reverse the conduit orientation to make the third bend?

If yes, I'm curious who is teaching the push-through method. I've done it myself but have never seen it taught [publicly].

Anyway, this sounds more like a rant than really wanting to discuss it.

 

[2Broke2Sleep]

Got it out of my NJATC apprenticeship book "Conduit Bending and Fabrication" (ATP published, no author given)

And yes, bender faces same direction throughout.

 

[2Broke2Sleep]

Ok, realized a couple things -(I should've caught this)when bending a saddle you are using a center of bend benchmark (rim notch for 45 on most hand benders) and not the arrow as in an offset, so the multiplier will change based on the difference between the arrow (for offsets) and the rim notch.

The multiplier changes for the push thru with the same concept in mind, only different reference points. (Center of bend to arrow for standard vs. Center of bend to center of bend for push thru)

The O.D. of the conduit bent is added to the multiplier of a push-thru because the multiplier leaves out the fact your conduit, when installed, must rest on the bottom and the calc ignores this fact.... Doing the calc for each side means ignoring the O.D. twice... so it is added back. An improvement could be made by incorporating the o.d. into the multiplier giving you different multipliers for each size/type of conduit....

Most guys I talk to on this topic get bored pretty quick but if you're doing a lot of RMC you are forced into these calculations from time to time....

 

[Smart $]

Only when I think back on my career do I realize I've probably run twice as much RMC compared to EMT or PVC. Fortunately about half the RMC was aluminum.

Can you scan or take a picture of the steps and calculations (and post, of course)?

The OD of the conduit should never really enter the calculations in my mind... so I'd like to see how and why the author works it in. Perhaps a clearance factor, I don't know because I don't have the whole picture.

FWIW (maybe some to other patrons), here's a link to the standard three-bend saddle hand bender method...
http://www.porcupinepress.com/_bending/saddles.htm

 

[2Broke2Sleep]

I can do so tomorrow. It's one of those things that is easy to get in hindsight....

 

[2Broke2Sleep]

 

[2Broke2Sleep]

Now I can do 4 bend offsets using the same logic

 

[steve_p]

Hi,

Have you seen the iBend pipe app for the smartphones? Really works well, has a level built in, really comes in handy.

 

[2Broke2Sleep]

Hi,

Have you seen the iBend pipe app for the smartphones? Really works well, has a level built in, really comes in handy.

I have not seen that particular app. Does it have the more technical layouts included? Segmented, cascading, parallel runs?

 

[Smart $]

...Can you scan or take a picture of the steps and calculations (and post, of course)?
...

View attachment 17465

Surely this is not what's in your NJATC apprenticeship book. :blink::huh:

 

[2Broke2Sleep]

Surely this is not what's in your NJATC apprenticeship book. :blink::huh:

No that's from yours truly.

 

[Smart $]

View attachment 17471
View attachment 17472

Hmmm.

I can't believe what I'm reading. This guy is saying the bend-to-bend distance multiplier changes because we are making a saddle bend and/or using different benchmarks... and then for push through bending we add the conduit OD. :roll::happysad:

I have to wonder if the author ever took geometry or trigonometry...

My bending techniques are based on traditional concepts—developed length, shrink, gain, tangent points, etc.

 

[Smart $]

My calculation for the push-through method.

 

[Smart $]

An exercise for the student.

• Conduit is 1" rigid
• Centerline bending radius is 6-5/16"
• Height of obstruction is 4-3/4"
• Distance to center of obstruction is 24"
• Developed length is 48"

What is the minimum straight length of conduit required?

 

[Fulthrotl]

An exercise for the student.

• Conduit is 1" rigid
• Centerline bending radius is 6-5/16"
• Height of obstruction is 4-3/4"
• Distance to center of obstruction is 24"
• Developed length is 48"

What is the minimum straight length of conduit required?

10'. maybe 20' if i screw up the first one.

 

[Smart $]

10'. maybe 20' if i screw up the first one.

You're not a student, so your answer doesn't count.

 

[Smart $]

My calculation for the push-through method.

Found error. New image. No d₁ or d₂, just d.

 

[Fulthrotl]

You're not a student, so your answer doesn't count.

i've been marginalized.... snif.

:weeping:

 

[Smart $]

An exercise for the student.

• Conduit is 1" rigid
• Centerline bending radius is 6-5/16"
• Height of obstruction is 4-3/4"
• Distance to center of obstruction is 24"
• Developed length is 48"

What is the minimum straight length of conduit required?

I'll even make it easy for y'all...

(BTW, this spreadsheet will work for offsets, too)