How do you calculate Gain in conduit bending The two methods we know do not get same result method 1-known radius and method 2-bending a 90 and calculating the difference. each method we get diff re?

Answer 1

With a known radius formula you use math to determine the difference between the straight line distance of the bend angle and the amount that a radius would trim the angle in the same senario. The 90 degree calculation method would be suitable for 90 degree fabrication, although it has to be considered that when measuring the finished piece, you are measuring the radius twice to get your result. In other words, if you use the known radius formula and you add the outside diameter of the pipe, you should have your 90 degree gain in theory. Also, if you measure the two sides of the 90 as a finished piece, and subtract the O.D. of the pipe, you should be close to the calculated number.

My answer to this question is a little different.

I have predetermined a lot of conduit bends and cut and threaded a lot of rigid pipe in my life. And I am sure that in some class, somewhere I probably had to do the math for this question, but through the years I have discovered that the gain is different for different benders shoes and for different pipe sizes, so it been my experience that a table is only a close estimate. And a formula is just another thing to have to either memorize and or write down and keep handy. So instead of trying to remember formulas or tables.

I simply take a stick of scrap pipe and measure it's length first, then write that measurement down on a piece of paper. Lets say our un-bent stick our pipe is 40" long.

Then i bend a perfect 90 degree bend in it.

After it's bent, I measure the stub length lets say it 12 " and lets say the the leg length is 32 5/8", I add them together and lets say I get 44 5/8" Next I subtract the 40" original pipe length from the 44 5/8" and get 4 5/8"; that is my gain, for that size of conduit, bent with that shoe on that bender on that job. I always assume the next jobs bender is probably going to be a little different then this one. And I'll have to do it again on that job.

Anyway after that I write that amount in my scratch note book for that pipe size and shoe, and subtract that amount from the next pipe i have to bend.

Then all you have to do is cut the pipe to length, put it the threader and cut the threads. Then take it out of the threader and bend your ninety in it. It will fit perfect.

Now if you have more then one 90 in the run you have to add the gain for each one. Then subtract the total of the 2-90's. Oh ya, you also have to add something for the thread's that go into the boxes, for the lock nut's and bushings.

Look on the side of the conduit bender. All the settings are there to bend perfect bends each time. The line across the benders shoe is for pulling point of bends and the star on the shoe is the starting point for shrink back bends. To fully appreciate the bending procedures that the bender can do read and understand the instructions that come with the bender. It will save you pipe and time in the long run.