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#206057 - 05/16/12 09:52 PM Back to back bends on electric bender
Merlin Offline
Member

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
I had to bend a back to back 90 with 2" IMC on a greenlee electric bender, today. I made the first bend and marked the conduit at the back of the next bend. When I lined that mark with the mark on the bender, my bend was 3" short. Anyone know what went wrong??? That is how my ugly book shows using a hand bender. What is the correct way?

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#206060 - 05/16/12 10:37 PM Re: Back to back bends on electric bender [Re: Merlin]
sparkyinak Offline
Member

Registered: 07/08/07
Posts: 1297
Loc: Alaska
Simple, you came up 3" short...

My thoughts and not to question your bending skills. Common bending problems:

*offsets are measured center to center of left to left, top to top, or bottom to bottom. Back to back 90's are measured outside to outside

*back to back bends requires the bender or pipe to be rotated 180 degrees for the second bend

*the tape measure got the better of the one who's doing the bending and measure wrong

The two bends in a back to back are bent from two different marks on the bender
_________________________
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#206075 - 05/17/12 08:53 PM Re: Back to back bends on electric bender [Re: Merlin]
Merlin Offline
Member

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
Obviousley I came up 3" short, but it wasn't a mis-measure. And yes I was measuring outside to outside. I also did rotate pipe 180 degrees. And, I made my first bend from the end of the shoe and second bend from the only notch in the shoe on this bender. That is what has me confused. There were 4 of us on this job and all confused about why this didn't work. We bend pipe almost everyday, but not usually 2" IMC. Most of what we do is 1 1/4" or less.

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#206076 - 05/17/12 09:22 PM Re: Back to back bends on electric bender [Re: Merlin]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Bend it long and cut the pipe to fit wink
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#206077 - 05/17/12 09:50 PM Re: Back to back bends on electric bender [Re: Merlin]
twh Offline
Member

Registered: 03/11/04
Posts: 898
Loc: Regina, Sask.
I think the notch marks something else, like the middle of ... ? Apparently the mark you want is 3 inches past the notch.

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#206080 - 05/18/12 09:24 AM Re: Back to back bends on electric bender [Re: Merlin]
allphase Offline
Member

Registered: 09/05/07
Posts: 14
Loc: Chicago il.
Did you figure in the shrink?

Bending of of c line you need to know the shrink


Edited by allphase (05/18/12 09:30 AM)

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#206092 - 05/18/12 08:53 PM Re: Back to back bends on electric bender [Re: Merlin]
Merlin Offline
Member

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
No, I did not figure in shrink. I used the formula from the "Ugly" book that is used for hand benders. I have not been able to find any other formulas for electric benders. Anyone know where to get bending formulas for this application?

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#206094 - 05/19/12 04:59 PM Re: Back to back bends on electric bender [Re: Merlin]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6805
Loc: Brick, NJ USA
Merlin:

Go to Greenlee.com & look thru the 555 documentation tab, download the PDF and there are basic instructions there.

They also have a decal that can be put right on the bender for reference.
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#206098 - 05/20/12 04:38 PM Re: Back to back bends on electric bender [Re: Merlin]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
Benfield Conduit Bending Manual

ISBN 978-0-87288-510-3
ISBN 0-87288-510-0

Priceless.

pg 20...

"In cases like this, the bender should be reversed and the bend made a w a y from the first bend [ flipping the conduit around 180 degrees, Ed ] as shown in Fig. 12. Instead of using the star-point symbol, use the arrow at the mouth of the bender and allow for the appropriate take-up as though making a simple 24" long stub-up bend."

In this particular example, the goal was back to back nineties snuck into a 24" space. First a stub was bent. Then, using its projected back-side dimension, a mark could be set, coming back the other way, measured as if a stub of 24" was desired.

For non-manual benders, this should be the standard routine.
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Tesla

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#206194 - 06/05/12 05:57 PM Re: Back to back bends on electric bender [Re: Merlin]
Bill39 Offline
Member

Registered: 11/28/01
Posts: 77
Loc: Indianapolis, IN, USA
It's been awhile but I believe this works:
Rise-gain = distance to add for a back-to-back bend.

I always measure my 90's to the back.

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