Hi Everyone! Need some help with calculating gain for a compound 90 deg. bend using 3/4" rigid Two 45 deg. bends will be used. I have no issue with the calculations to bend the pipe, I just need advice on calculating the gain so i can cut and thread before bending to arrive at my total length when done. Thanks
Calculating gain for a compound 90 deg. bend/rigid conduit
- Thread starter tld38
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masterinbama
Senior Member
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- Huntsville Alabama
Off the top of my head I would say your gain will be the same as for a 90 plus half the distance between your bends. Practice on a piece of emt.
What are you using to bend it?
What is the centerline radius of the shoe?
You'll gain 0.343" for every inch of the 45? dog-leg out of the 90? corner (measured inline with stub and tail centerlines to intersection of dog-leg centerline)**, and you'll gain 0.043" for every inch of centerline radius for each 45? bend. (I think... just coming off 12 hour shift... brain not functioning normally :blink
** For example, if you are a foot out of the corner (plus half the diameter of the conduit and any spacing off the wall), your dog-leg would be 1.414' long and your measures along stub and tail centerlines would be 2' total (1' each way). A gain of 0.686'.
What is the centerline radius of the shoe?
You'll gain 0.343" for every inch of the 45? dog-leg out of the 90? corner (measured inline with stub and tail centerlines to intersection of dog-leg centerline)**, and you'll gain 0.043" for every inch of centerline radius for each 45? bend. (I think... just coming off 12 hour shift... brain not functioning normally :blink
** For example, if you are a foot out of the corner (plus half the diameter of the conduit and any spacing off the wall), your dog-leg would be 1.414' long and your measures along stub and tail centerlines would be 2' total (1' each way). A gain of 0.686'.
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- Location
- New Jersey
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- Journeyman Electrician
Smart will give you the smart answer, I will give you the dumb answer. Make a few marks on a scrap piece of conduit say 48", make the first mark at 6" and the second at 12' then bend the 2-45?'s. Find the overall gain (the new length compared to the original 48") and then adjust your marks to fit what you need.
Cow
Senior Member
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- Eastern Oregon
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- Electrician
I think this is how most folks do it, I know I do. There is a always a scrap piece laying around to test it on, and it will give you real world results of what YOUR bender will give you for gain. I could do it Smart's way and the bender would probably still spit something out a little off....it's easier to use a test piece IMO.
It helps if you keep notes on this stuff too, so you don't have to do a test piece on every job.
Smarts answer is deep into the Trig...he is referencing the shrink, which like an offset being bent is roughly 1/8" per 15 degrees per 1" of rise (or elevation change).
Nobody can tell you exactly what your gain will be as it depends on the shoe of the bender being used. Infinity's answer is the best, with a scrap piece of pipe chart your bender.
Also keep in mind, your gain will change (as will your shrink) with an increase or decrease in distance between your two 45 degree bends.
Actually, the best way is to just bend the thing with extra long stub and tail, then cut and pony thread.
Approximating the gain through one 45? bend for the dog leg will not be much different than actual... especially considering field measuring actual gain is relatively imprecise compared to measuring actual gain of a 90? bend.
Approximating the gain through one 45? bend for the dog leg will not be much different than actual... especially considering field measuring actual gain is relatively imprecise compared to measuring actual gain of a 90? bend.
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