Bending a 90 degree "backwards"?

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frequency

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Hello all,

I'm new at posting messages. This forum has been very informative and humbling.

My Question: I'm still learning how to make bends using one length of raceway but I was asked a question from the lead journeyman while bending 3/4" EMT. He said,"do you know how to bend a 90 backwards?" I could not answer him. I wanted to say using "star" but i'm not certain. Please help. All responses are greatly appreciated. Thank you all for your time.
 
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frequency

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Same here, I never heard of that, either.
I said what do mean?
He claims that if you had a 90 @ 8'(measuring left to right) so rather then bend most of the pipe, you would deduct for 90, 3/4" emt = 6" then divide by 2= 3". This would be 93 inches? use arrow and bend. I might not be explaining this correctly and hope this makes sense. Thanks for the link, Edward!
 
infinity

infinity

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frequency said:
Same here, I never heard of that, either.
I said what do mean?
He claims that if you had a 90 @ 8'(measuring left to right) so rather then bend most of the pipe, you would deduct for 90, 3/4" emt = 6" then divide by 2= 3". This would be 93 inches? use arrow and bend. I might not be explaining this correctly and hope this makes sense. Thanks for the link, Edward!
Click to expand...

Yup, just add 1/2 of the standard deduction for that bender and bend the other way. Comes in very handy when you need to make a long elbow or a back to back bend.
 
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ggunn

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My first impulse was that it was a hazing question, like "go get me a left handed crescent wrench". :D
 
Little Bill

Little Bill

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frequency said:
Same here, I never heard of that, either.
I said what do mean?
He claims that if you had a 90 @ 8'(measuring left to right) so rather then bend most of the pipe, you would deduct for 90, 3/4" emt = 6" then divide by 2= 3". This would be 93 inches? use arrow and bend. I might not be explaining this correctly and hope this makes sense. Thanks for the link, Edward!
Click to expand...

What your journeyman is saying is bend the short stub rather than bend the long end up, especially if overhead room is a problem.
 
Smart $

Smart $

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infinity said:
Yup, just add 1/2 of the standard deduction for that bender and bend the other way. Comes in very handy when you need to make a long elbow or a back to back bend.
Click to expand...
Why do that when the star mark already does that for you?

Also, adding 1/2 the deduct and bending "backwards" would give you a bend that is a little long. According to my calculations, the add amount is closer to 45%.

If you are using a bender that does not have a star mark, such as a 555, you'll need to determine the gain. Put a 90 on a straight, known-length of conduit (you can do this with a piece you intend to use, or a scrap piece... your choice). Measure the resulting two lengths, add the lengths, then subtract original straight length. This gives you the gain. To make a backwards bend, deduct the gain, then add the standard "deduct" to get the "backwards" bend mark.
 
Smart $

Smart $

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Smart $ said:
... To make a backwards bend, deduct the gain, then add the standard "deduct" to get the "backwards" bend mark.
Click to expand...
Diagram...

reversebendmark.gif


Found an old diagram I posted previously. Note the direction is reversed.

reversebenda90.gif
 
Smart $

Smart $

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Location
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ActionDave said:
Because you use the same mark on your bender everytime.
Click to expand...
Well, I must say it is a reason... but I can't decide how much merit to give it :D

I can see it being beneficial if one person is doing the measuring and another bending. On those occasions where I'm doing the measuring, I make a sideways, stubby T as the bend mark (see second diagram I posted), so there was no question as to which direction to bend.
 
Smart $

Smart $

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Smart $ said:
... adding 1/2 the deduct and bending "backwards" would give you a bend that is a little long. According to my calculations, the add amount is closer to 45%.

...
Click to expand...
Rethought this and determined it is wrong. Adding 1/2 the "deduct" would result in a bend that is a little short. I originally figured the gain to deduct ratio when it should have been the (deduct minus gain) to deduct ratio. The calculated add amount is 54-55% of "deduct" value when bending 1/2" and 3/4" EMT in a typical hand bender: 2.7" and 3.3" respectively.
 
ActionDave

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Smart $ said:
Why do that when the star mark already does that for you?

Also, adding 1/2 the deduct and bending "backwards" would give you a bend that is a little long. According to my calculations, the add amount is closer to 45%..
Click to expand...

ActionDave said:
Because you use the same mark on your bender every time.
Click to expand...
Update- I tried two bends using star last night, one reverse bend and one back to back ninety. Both times I came up short, about one half inch.
 
Smart $

Smart $

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ActionDave said:
Update- I tried two bends using star last night, one reverse bend and one back to back ninety. Both times I came up short, about one half inch.
Click to expand...
The bender is faulty :p

Curious... what make/model bender are you using? Are you lining up the mark and star like this...?
BendingbyStar.gif
 
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