Another pipe bending question

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Marxllc

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I have the need to bend some 3/4 emt, that would be kind of like the top of a q/tip I am assuming 180 degrees, 4ft wide outside to outside, any thoughts on how to accomplish this
 
Like the top of a Q tip? Huh?
Are you trying to bend back to back 90's?


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Marxllc said:
I have the need to bend some 3/4 emt, that would be kind of like the top of a q/tip I am assuming 180 degrees, 4ft wide outside to outside, any thoughts on how to accomplish this
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If you're going around something, use pulling elbows. U's look terrible. Also for $1.99 at the App Store is iBend Pipe, which will answer any bending question you may ever have.
 
Marxllc said:
I have the need to bend some 3/4 emt, that would be kind of like the top of a q/tip I am assuming 180 degrees, 4ft wide outside to outside, any thoughts on how to accomplish this
Click to expand...

I recommend starting with a scaled drawing of your conduit path, so you know how much straight length there will be between each bend. Here's a reference for the bend radii. Although it isn't specified, this refers to the centerline bend radius. 3/4" conduit has a centerline bend radius of 4.5", which is the minimum allowable by the NEC. Standard radius factory elbows will be built to this spec. First draw the centerline path, then offset by the radius of the EMT size. You can assume that centerline length is "conserved" when you do a bend.
http://www.lanshack.com/DesigningConduitRuns.aspx
 
If you are trying to bend a 180 hairpin/sheperds crook turn and end up with the two sections of pipe close together, you may have a problem with interference between the pipe and the bender handle.
Could you make the bend out of plane (like a corkscrew) and then flatten it out once you had the 180 + bend?
 
4ft bend of EMT.jpg

Here's a scaled drawing of this bend.

See the outer diameter of 3/4" EMT, and the centerline bend radius. Based on the 4 ft out-to-out dimension, you'll need 38 1/16" of straight length between bends.
 
Marxllc said:
I can not use the back to back or fittings, this is for an in floor heating system for a freezer, I need it be smooth for pulling the heat cable,
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Are you able to make a wide radius bend? You can approximate a wide radius bend, with many sequential bends of standard radius, and short straights between. Make it like half of an octagon with rounded corners, or similar shape.
 
That bend 4ft wide? I would take the bender take small bites and start gradually rolling it into shape.

That is if I were to bend such a odd bend:)

Your going to have to bend it slightly skewed so it can go by the handle and straighten it out once you get done.
 
Just get the job done.

Just get the job done.

Marxllc said:
I can not use the back to back or fittings, this is for an in floor heating system for a freezer, I need it be smooth for pulling the heat cable,
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I don't understand the prohibition of fittings. Are you planning to bury this in concrete? If so who would know (or care)?

Get an conduit coupling and measure how close the two ends placed in it can come together. Call it G and write it down.
Take two sticks of conduit, make a 90 degree bend three feet from the end of both sticks.
Lay them on the floor with the two bend parts facing each other, slide them together, side by side, until the two legs are at the proper distance apart.
Now slide them towards each other by the distance called G.
Mark one of the pipes where the end of the other one is.
Cut at the mark, and ream.
Connect the two with the coupling. done.

Sometimes we look for the perfect solution, when a good-enough solution is -- good-enough.
 
If you want a fairly perfect radius across a 4 foot "U" shape you need to learn how to do multi-shot bends. Is more accurate if using mechanical benders that can indicate small bend amounts more accurately compared to trying to do it with hand benders. I haven't done it in 25-30 years when I was in school, but you essentially need to calculate how many bends you need, how far between them and how many degrees to bend at each point.
 
kwired said:
If you want a fairly perfect radius across a 4 foot "U" shape you need to learn how to do multi-shot bends. Is more accurate if using mechanical benders that can indicate small bend amounts more accurately compared to trying to do it with hand benders. I haven't done it in 25-30 years when I was in school, but you essentially need to calculate how many bends you need, how far between them and how many degrees to bend at each point.
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It's called 'incremental bending' and doing it with a hand bender is about impossible. A 'Chicago' type bender is the best, along with a no-dog and a magnetic inclinometer.

Do as many bends at as few degrees as possible. This isn't a bend for beginners as the mistakes in the bends all add up.

Your drawing show 6 30 degree bends. I would try for 12 15's, it would look better.
 
K8MHZ said:
It's called 'incremental bending' and doing it with a hand bender is about impossible. A 'Chicago' type bender is the best, along with a no-dog and a magnetic inclinometer.

Do as many bends at as few degrees as possible. This isn't a bend for beginners as the mistakes in the bends all add up.
Click to expand...
Though just bending one pipe will be easier, especially if you can have some tolerance in the outcome.

Bending multiple pipes that you want to lay side by side with perfect symmetry is definitely more of a challenge.
 
I once had to bend some 1/4 inch round bar to a (fairly) precise sine wave showing better than 2 complete cycles p-p one foot, heating it w/ a torch to soften it. I drew the sine wave I wanted on paper, and bent and compared the rod to the paper (burned a couple of templates, but that is part of the fun.:p

 
Find yourself one of the old folding "tape measures". They are hinged to allow you to make different angles. Set it up and make your bends to it.

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Marxllc said:
This would work, how about a formula
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It would be the radius times 1/2 pi for a 90° bend, so you will need radius times pi for the straight length of conduit needed for your bend. Divide the total length by the number of bends you will use and mark the conduit at those points and bend.

When we did this with rigid conduit we would use 18 five degree shots for a ninety.

It is much easier with a Chicago type bender, but you can do it with a hand bender.

We also used a length of dress makers elastic to lay out the 18 marks on the conduit. We put 18 evenly spaced marks on the elastic and use those marks to mark the bending points on the conduit. You put marks for the total length on the conduit and then stretch the elastic between those two marks to show you where to put the remaining 16 bending marks. Way faster than doing the math and measuring out for each mark.

This was for a flat conduit rack where the specs requires concentric bends....some of the bends on the outside of the rack took more than 10' of conduit for the 90.
 
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