Like I guess it's called, a rolling offset. I have the green book from Mr. Cox on bending. I don't see anything on matching existing bends. Do I need to find the pipes center of bends, and degree? Then mark that measurement on a new stick, and bend it at the center mark on the hand bender? This is probaley a tough one to answer on a forum. A guy I was working with showed me a formula like square this number, then square this number, then add them, then find the square root of that number. Sound familar? The guy lost me, I don't know what measurements he's talking about. Thank you for your help.
How to match existing conduit bends
- Thread starter zappy
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masterinbama
Senior Member
- Location
- Huntsville Alabama
I use the trig table in my ugly's book. The Co Secant of the angle is your multiplier for offset bends.
http://www.math.com/tables/trig/tables.htm
http://www.math.com/tables/trig/tables.htm
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I was trying to avoid replying... as you said, difficult to answer on forum. But since you've only had one answer thus far, I'll at least put in a word... :angel:
First off, a rolling offset is typically just an offset which is installed in a non-vertical, non-horizontal plane. If your measures for a rolling offset are vertical and horizontal, square and sum those measures, then take the square root of the sum for the amount to offset. In measuring vertical and horizontal, keep clearances in mind... as you may have to add the full or half the diameter of the conduit, or not.
Beyond that, matching an existing bend is determining where and how much to bend, and how close you want or need to match. Essentially, you want to measure for the manner in which you will bend. Measuring for the center of the bends is fine if you are bending from the center... but hand benders bend from the theoretical tangent point, i.e. where straight meets bend. One way to match is to first determine angle of bend to match, as best you can. Then on a [scrap] piece of conduit, make your bend mark all the way around the conduit and bend. Hold this piece next to the bend to match so that it is aligns perpendicularly, i.e. the bends touch at their sides. Check your angle for match. If good, put a mark on the existing where the scrap piece's bend mark touches. You now have a mark to measure from for your new piece's bend mark.
Flip the scrap piece over and repeat above procedure for second bend. The transferred bend mark should be on the angled part of the existing run. Now using a flexible rule, such as a tape measure, measure between transferred bend marks following the surface of the conduit around the bend. Not an exact measure for distance between bends being just a tad long... but compare this measure with other methods (e.g. offset amount times cosecant) of determining distance between bend marks.
mgmelec
Member
- Location
- new jersey
take a look at these videos. http://www.ibewhourpower.com/JobTips.aspx look for the video with a folding rule.
K8MHZ
Senior Member
- Occupation
- Electrician
What size conduit???
Making copies of bends in 1/2 inch pipe with a hand bender is a different animal than making them with 1 inch on a Chicago or 2 inch on a 555.
Angles can be copied using a folding rule. I didn't follow the link, but that's probably what it was about. Distances between bends can be copied by marking the centers of the bends and measuring them.
More 'by eye' skill is needed using hand benders, where larger, stationary benders can use levels (No Dogs) and magnetic protractors. A person that knows how to use a Chicago can make the most precise bends you have ever seen.
You also didn't tell us if the pipe had to be exact (like for aesthetics) or is it meant to just work. If it is a 'just make it work' bend, a coupling for the rolling part of the bend if probably cheaper than trying to make an exact copy using a bender. The fact that you are asking for help on the Internet tells me that you are going to spend a bit of time, and perhaps waste some pipe, trying to make the copy. Time is money. Use a 'cheater' and get on with it.
Making copies of bends in 1/2 inch pipe with a hand bender is a different animal than making them with 1 inch on a Chicago or 2 inch on a 555.
Angles can be copied using a folding rule. I didn't follow the link, but that's probably what it was about. Distances between bends can be copied by marking the centers of the bends and measuring them.
More 'by eye' skill is needed using hand benders, where larger, stationary benders can use levels (No Dogs) and magnetic protractors. A person that knows how to use a Chicago can make the most precise bends you have ever seen.
You also didn't tell us if the pipe had to be exact (like for aesthetics) or is it meant to just work. If it is a 'just make it work' bend, a coupling for the rolling part of the bend if probably cheaper than trying to make an exact copy using a bender. The fact that you are asking for help on the Internet tells me that you are going to spend a bit of time, and perhaps waste some pipe, trying to make the copy. Time is money. Use a 'cheater' and get on with it.
Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
there are two groups of people in the world.... center to center, and
outside to outside.... and it's always fun watching one of each of them
try to work together to get something bent....
i'm assuming this is with EMT, and it's a big enough diameter pipe that
you can't scooch it easily... lets' say 4" emt, for sake of argument....
i can show you the math to do "rolling" or compound offsets, but you don't
need that, you need to get this done...
get a scrap of 1/2" emt a couple feet long, bend it to match the pipe you
are trying to match..... take it down and measure the angle with a digital
level. don't have one? they aren't expensive.... consider the purchase of
one.
hold a straight piece of 1/2" emt alongside the target pipe, measure how
much offset there is, measuring with the axis of the offset.... in line with
it, so to speak.
now, you have an angle and an offset amount, center to center.
go bend it, leaving it a few inches longer than the pipe you are gonna
match.... put it up in place, and cut the end where you want to have
the coupling if you want it to match.
install pipe.
have fun.
now, if what you mean is doing something of a concentric nature,
there is a good way to do that, but it involves segment bending,
a piece of elastic with 1" marks on it, and the willingness to learn
how, which means ruining some pipe.
and learning about developed length.
if you are doing ridgid, and have to cut and thread before bending,
the quick and dirty way i just mentioned may not work for you.
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jmellc
Senior Member
- Location
- Durham, NC
- Occupation
- Facility Maintenance Tech. Licensed Electrician
I had to match some odd angle offsets several years ago. I had good results with a small magnetic protractor. I put it on the offset and found a 55 degree angle. I measured center to center of the bends and bent mine to 55 degrees with same distance on bends. Came out with no more variance than the 10 or so offsets already there. I was pleased with it.
I was using 3/4 EMT, same as other conduits. I may have had to do more trial & error if it had been a different size.
I was using 3/4 EMT, same as other conduits. I may have had to do more trial & error if it had been a different size.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
LMAO - been there. I can never get into the heads of the "outside," offsets from the arrow, and 30s on the floor guys.
sandking
Member
- Location
- Southern California
I would match center of bend to center of bend. Regardless of the size of conduit, the center of the bends will always be the same. Now, finding the exact center on your bender could be the hardest part depending on the bender, but the hand benders have it done for you. No math needed for this method :thumbsup:
Hand benders only have center of bend mark for a specific angle of bend (typically 45 or 60? depending on bender). The mark won't do you much good for any other angle of bend.
FWIW, I made up a chart of angles measured with a 5/8" wide 72" folding rule...
https://docs.google.com/viewer?a=v&...MzYzOS00YzlkLThlOWMtMTkzZDFiMDdmMmY4&hl=en_US
https://docs.google.com/viewer?a=v&...MzYzOS00YzlkLThlOWMtMTkzZDFiMDdmMmY4&hl=en_US
sandking
Member
- Location
- Southern California
jmellc
Senior Member
- Location
- Durham, NC
- Occupation
- Facility Maintenance Tech. Licensed Electrician
If you must, you can bend using the forward arrow. That will get the right bend, then you can cut off the ends as needed, to position the offset. If doing this, a short piece of conduit is less wasteful than cutting off from a whole stick.
Your gonna have to explain what you mean...
sandking
Member
- Location
- Southern California
Really? It's an angle "finder". You place this on the existing angle to see what it is via the digital display, then bend your new one to the same angle.
quogueelectric
Senior Member
- Location
- new york
pipe bending 101
pipe bending 101
There are many different methods to bend pipe pick one and I will try to help you understand it better..... A rolling offset is still a parallel set of bends yet are rolled to a plane not horizontal and not vertical to pass an obstruction or find a support what is needed to know is the TOTAL offset depth rather than getting into crazy math.
pipe bending 101
There are many different methods to bend pipe pick one and I will try to help you understand it better..... A rolling offset is still a parallel set of bends yet are rolled to a plane not horizontal and not vertical to pass an obstruction or find a support what is needed to know is the TOTAL offset depth rather than getting into crazy math.
quogueelectric
Senior Member
- Location
- new york
Most peple run into trouble when they have to make a shallow kick or a shallow offset on pipe as this is not attainable with standard 30 or 45 degree factory elbows. If I know I will need custom bends I will call to a job with a bender set up and have them make a couple of 5 degree offsets on a few lengths of pipe. I can make any height kick or offset with these by just cutting the filler length in the middle to give you your desired length of kick.
I know that part... but we were/are talking about bending to match using the center of the bend, for existing to measure and for new to match. How do you use a digital angle finder to duplicate the bend at a specifc point on the conduit? Yes, bend long and cut off excess is one method... but can you can you place the bend exactly where it needs to be without cutting?
sandking
Member
- Location
- Southern California
Of course nobody is perfect and the possibilty of a boneyard is quite high if you plan to bend it EXACTLY like the existing situation with a practice piece or having to swallow the pride and cut a piece off.......... But, you can easily get real damn close if you try hard enough. The way "I" would do it is, start from the closest end of the conduit and measure to the center of the existing bend, lets say its 20". Now, I would measure from that 20" to the center of the next bend, lets say its 40". Now you know your center to center of bends are 40" apart. Then, I would look at the bender, either a hand bender or a shoe depending on size and I would determine where I "think" the center of the bend is (practice on scrap if needed). Once you find center of the bender, you can deduct the distance from that center point to the start of the bend, then repeat for the 2nd bend. The angle finder comes into play before you can find the center of the bend. The degree of bend will obviously dictate the center of the radius. Everybody does things differently, and results will vary, but this seems to work quite well for me.
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