Bending Conduit

[GLSA]

Besides using a bending app is there any book or formula that will show you the layout on a piece conduit where the offset sits up tight to the obstruction without cutting the conduit to fit exactly.

So for example, if the distance to the obstruction is 30" from the last coupling and the offset I want to use is 6", where would I put my marks and what bender mark would I use. In the past, for this scenario, I would never get too technical. I would come back 10 or 15 inches from the coupling make a mark and then make my next mark at 12 inches from there and bend it using the front of the shoe as my mark. The conduit did not sit up tight to the obstruction but it was really never that important. The job I am on now I have to be more precise.

 

[Carultch]

Besides using a bending app is there any book or formula that will show you the layout on a piece conduit where the offset sits up tight to the obstruction without cutting the conduit to fit exactly.

So for example, if the distance to the obstruction is 30" from the last coupling and the offset I want to use is 6", where would I put my marks and what bender mark would I use. In the past, for this scenario, I would never get too technical. I would come back 10 or 15 inches from the coupling make a mark and then make my next mark at 12 inches from there and bend it using the front of the shoe as my mark. The conduit did not sit up tight to the obstruction but it was really never that important. The job I am on now I have to be more precise.

If you are good at drawing it to scale, you can accurately draw it in a CAD program or on graph paper, and measure the arc-length along the center line. Centerline length is conserved during a bend.

 

[Smart $]

Besides using a bending app is there any book or formula that will show you the layout on a piece conduit where the offset sits up tight to the obstruction without cutting the conduit to fit exactly.

So for example, if the distance to the obstruction is 30" from the last coupling and the offset I want to use is 6", where would I put my marks and what bender mark would I use. In the past, for this scenario, I would never get too technical. I would come back 10 or 15 inches from the coupling make a mark and then make my next mark at 12 inches from there and bend it using the front of the shoe as my mark. The conduit did not sit up tight to the obstruction but it was really never that important. The job I am on now I have to be more precise.

Assuming you are using a hand bender, you'd measure 30" plus 6 times the per inch shrink of a 30° offset, and mark.... subtract or measure back 12" from that and put another mark. Bend with your shoe backwards to the direction of measure, with the marks on the conduit aligned to the normal bend mark on the shoe.

PS: the shrink per inch of offset is 1 - cos(bend angle)... which is 0.134" for a 30° offset. Most use 1/8" in the field.

 

[Johnnybob]

You really don't want an offset to sit up tight anyway, the radius needs to stand off a bit from the obstacle to prevent rubbing.I forget what the constant is for that, I think 5" for some reason. Richard Cox's "Electricians Guide to Conduit Bending" is very informative for that sort of question. I haven't bent EMT in so long my hand benders are all dusty, if I could find them. I bend everything on a 'Chicago' or 555.

 

[GLSA]

Assuming you are using a hand bender, you'd measure 30" plus 6 times the per inch shrink of a 30° offset, and mark.... subtract or measure back 12" from that and put another mark. Bend with your shoe backwards to the direction of measure, with the marks on the conduit aligned to the normal bend mark on the shoe.

PS: the shrink per inch of offset is 1 - cos(bend angle)... which is 0.134" for a 30° offset. Most use 1/8" in the field.

Ok I get the first part but I was taught as an apprentice that you face the front of the bender towards the measurement unless it is the back of a 90. So in my case, I did calculate the shrink (but I used 1/4"), I made my marks at 19.5" and 31.5" and made my first bend at the 19.5" mark using the front of the shoe as my reference and moved to the second bend with the front of the bender facing away from the obstruction for both bends and this did not work.

If I understand you correctly my marks are right but the front of the bender needs to face towards the obstruction and my first bend should be the 31.5" mark and the second at 19.5 inches? I normally use the front of the shoe for my reference. Do I need to use the arrow in this scenario?

Also, do you always face your bender backward to the direction of the measurement because if your offset is within the first 4' of the conduit then you do not have a lot of leverage for the second bend depending on the rise and angle of your offset?

Thanks

 

[Smart $]

Ok I get the first part but I was taught as an apprentice that you face the front of the bender towards the measurement...this did not work.

That's because your 30" measurement plus shrink is not to the beginning of the last inline bend (i.e. closest to obstruction), it is the end of the last inline bend... and that's why you have to turn the bender around.

If you want to bend with the bender "facing" from whence measured from, you'd have to subtract (30°/180°)(pi)(r), which is the length of conduit in the bend, from the measurements previously stated. For example, if you are bending 1/2", it has a 5" radius. 3.14...× 5" ÷ 6 = 2.617" or 2-5/8". You'd put your "long" bend mark at 30" + (6×1/8") -2-5/8" = 28-1/8" and your "short" bend mark at 28-1/8" - 12" = 16-1/8". Place bender facing from whence measured.

If I understand you correctly my marks are right but the front of the bender needs to face towards the obstruction and my first bend should be the 31.5" mark and the second at 19.5 inches?

Correct.

I normally use the front of the shoe for my reference. Do I need to use the arrow in this scenario?

Correct.

Also, do you always face your bender backward to the direction of the measurement because if your offset is within the first 4' of the conduit then you do not have a lot of leverage for the second bend depending on the rise and angle of your offset?

Not always... especially for the very reason you stated. I gave you the means above to flop the mark and bender around to bend in the opposite direction.

 

[MiElectrician]

Point the hook the same way you pointed your measuring tape. The calculation you did was close bit it would make it an inch long, with emt it's easy enough to shave an inch off and some people always measure long on the first bend. Arrow is the start of the bend. Never heard of using the front but I think it's throwing you off. You want your second mark to be exactly where the obstruction starts, that is past the radius of the bend and makes it look like you made the bend for the obstruction, rather than a random bend before an obstruction.
I spent my first several months as an electrician bending emt and grabbed uglys guide to conduit bending and read it and practiced and now I'm one of the better benders in the company even though I don't have much experience. Most people just guess and cut, if you can mark out a couple bends and have everything line up you're doing alright.

http://www.contractorresource.com/u...gYvS8eVWUwT5o2xMxqqz6wk6K4vfu_v5QchoCqR_w_wcB