Rolling offset...help needed please.

[tds73]

Maybe this is not the right forum,but here it goes.

I am stumped. I need to draw a rolling offset of a piece of 30" round duct. What it needs to do is connect 2 pieces of straight that are offset to the side and at different elevations. Trouble is, i am using a 3rd party software that is autocad based and I cannot figure out how to come up with angles to get the connection to work. I am trying to use 2 45 degree elbows and install them "rotated" on existing pipe and add a piece of straight inbetween and connect. I have been trying all I can think of and just cannot seem to make it work. I have used the pythagorean theorem, rolling offset formulas(from piping handbook) and geometry and just cannot figure the right combinations to make it work. Maybe 45 degree elbows are not the right choice.Maybe I am using the wrong radius on the 45's. I am stuck and frustrated. I was hoping someone on the forum would know what I am looking for and maybe where I could look for some info.

Quick rundown of scenario:

first pipe is 30" round. second pipe is 30" round and is running same direction(or parallel) as first. the end of pipes are 132.5" apart(face to face or delta y). The centerline elevation is 69" different(delta z). The centerlines are offset by 69"(delta x).

I hope that makes sense. Please help and thank you.

[Tankman]

Try lookin' at www.thesheetmetalshop.com.

 

Years ago I was a sheetmetal layout man. Loved the work.

 

At one time I did a lot of large duct through which raw cotton was blown.

The cotton actually would wear out the el's which we fab'd from Core 10 steel to

make them last longer.

 

Was interesting work.

 

At the sheetmetalshop.com website, click on library.

The books are in *.pdf format, save to your HDD for reference.

[Tankman]

tds73, can you post your drawing?

 

Some viewers might not have '07, so, save in 2000 format if you want to post the *.dwg file.

 

I have the basic view in my mind but, not sure.

[tds73]

I have a quick sketch up dwg. I do not know how to post the .dwg. it is 497 kb. it is drawn with the existing pipes shown and a single line between them. One could 3d orbit to see it more clearly. Just not sure how to add it to post.

[Tankman]

I have a quick sketch up dwg. I do not know how to post the .dwg. it is 497 kb. it is drawn with the existing pipes shown and a single line between them. One could 3d orbit to see it more clearly. Just not sure how to add it to post.

 

When posting, go to advanced, click on the paper clip, upload file.

[rkent]

I drew this in 3d and dimed the angles. the view will be the same in top view of side view.

[tds73]

rkent,

that is it. question is, how do you get to that? i even tried to use a sweep, but either i was doing it wrong, or you cannot sweep along something not on the same plane.

once i learn how to get what you have drawn, which is the existing line, i need to draw another line of different diameter next to it, at a different angle to get under and cross the existing line. i believe once i have a grasp on how exactly to arrive at what you drew, i will be able to figure out how to draw the other line.

i think i have been in the right book , just on the wrong page.

[rkent]

rkent,

that is it. question is, how do you get to that? i even tried to use a sweep, but either i was doing it wrong, or you cannot sweep along something not on the same plane.

once i learn how to get what you have drawn, which is the existing line, i need to draw another line of different diameter next to it, at a different angle to get under and cross the existing line. i believe once i have a grasp on how exactly to arrive at what you drew, i will be able to figure out how to draw the other line.

i think i have been in the right book , just on the wrong page.

 

I drew a line, then copied it endpoint to endpoint. Then I moved the line 69" in the Y axis, then 69" in the Z direction. Then I drew a line between the endpoints. I listed that line length, I think it was 8'1.5", so I stretched one of the original lines by that length to shorten it, then drew a line between those endpoints to get the hypotenuse, rotate the UCS to match the angle, drew a pline on top of those lines, use a fillet of 45", finally drew the 30" circle and extruded (sweep would work as well).

 

There is probably a much faster way but that worked for me. Actually, I have a little book that has the math, "IPT's Pipe Trades Handbook", you should pick one up.

[tds73]

Rkent,

sorry it took so long for me to reply. so i followed your example and arrived at what you have drawn. if i am seeing this correct,you said the side view will be same as top view, that makes sense to me but how do i actually get this thing place so that when i go into 3d orbit it shows this? what i mean is, placing the one end in the correct "z" location to reflect actual view in 3d. Does that make sense?

Also, I am no math wiz, by any means, but does your drawing represent 45 degree elbows rotated about the xor y axis or are they 35 degree elbows?

i may have gotten in over my head, but now i am determined to figure this out.

Bottom line is that once i get this line drawn in, and in the correct x,y,z locations, i need to draw in another line next to it, at a different angle in the z direction and have it turn under to get past existing line.

then the goal is to draw both lines, in 3d and be able to orbit around and see that they clear each other.

i hope all that mumbling makes sense.

[rkent]

sorry it took so long for me to reply. so i followed your example and arrived at what you have drawn. if i am seeing this correct,you said the side view will be same as top view, that makes sense to me but how do i actually get this thing place so that when i go into 3d orbit it shows this? what i mean is, placing the one end in the correct "z" location to reflect actual view in 3d. Does that make sense?

 

As I said, draw a line, then copy it 69" in the y direction, then move it 69" in the Z. When copying in the Z you can do this pretty easily. Copy, pick your object(s), enter, (do not pick a displacement point) simply enter 0,0,69 and hit enter twice.

 

Also, I am no math wiz, by any means, but does your drawing represent 45 degree elbows rotated about the xor y axis or are they 35 degree elbows?

 

Those are 45 degree ells. They are rolled in the Z direction 45 degrees.

 

i may have gotten in over my head, but now i am determined to figure this out.

Bottom line is that once i get this line drawn in, and in the correct x,y,z locations, i need to draw in another line next to it, at a different angle in the z direction and have it turn under to get past existing line.

then the goal is to draw both lines, in 3d and be able to orbit around and see that they clear each other.

i hope all that mumbling makes sense

 

So lets go over some basics for 3d in AutoCAD. You know about the preset views for viewing in iso views? View, pick SW Isometric, set current, ok.

The problem with viewing 45 degree objects in an Iso view is that it doesn't really show that well. This has been a problem for ever and is tough to show in 2d isometric drawings. Adding some Iso lines helps show what is going on.

 

 

It sounds like you know about 3dorbit, there is also 3dforbit (sorry not in 2007).

 

Do you know how to manipulate the UCS? Type UCS and look at the command line. You can use OBject to select a line, you can simply pick an endpoint and then two directions to describe the X and Y. You can rotate about the X, Y, Z axis, etc. If you don't know these well you will need to go through help, or a book to get comfortable with the UCS.

 

I will post a few more screen shots that hopefully will help. Keep plugging along, you are in the same part of the learning curve so many of us went through. Only the ones that stay with it will come out the other side victorious.

[tds73]

As I said, draw a line, then copy it 69" in the y direction, then move it 69" in the Z. When copying in the Z you can do this pretty easily. Copy, pick your object(s), enter, (do not pick a displacement point) simply enter 0,0,69 and hit enter twice.

 

no issues with this part.

one question i do have though is, am i correct that you cannot sweep along a pline that changes elevation?

 

Those are 45 degree ells. They are rolled in the Z direction 45 degrees.

 

i see them clearly now. it is making more sense.i was thinking for some reason that the elbows would be rolled other than 45 deg.

 

i have them drawn now just like your example. now i am going to fumble around with my next step.

So lets go over some basics for 3d in AutoCAD. You know about the preset views for viewing in iso views? View, pick SW Isometric, set current, ok.

The problem with viewing 45 degree objects in an Iso view is that it doesn't really show that well. This has been a problem for ever and is tough to show in 2d isometric drawings. Adding some Iso lines helps show what is going on.

 

 

It sounds like you know about 3dorbit, there is also 3dforbit (sorry not in 2007).

 

Do you know how to manipulate the UCS? Type UCS and look at the command line. You can use OBject to select a line, you can simply pick an endpoint and then two directions to describe the X and Y. You can rotate about the X, Y, Z axis, etc. If you don't know these well you will need to go through help, or a book to get comfortable with the UCS.

 

i can manipulate the ucs to an extent, use it on to move my background drawings to get things to 90 degrees to make it easier for me to place duct and annotations when building is at an angle on drawings.

I am slowly getting better at being able to see and understand the ucs in terms of x,y,and z as i am trying to place objects or draw in 3d. i use the 3d orbit often to make sure objects are missing each other or are aimed the right direction.

now i am going to try to figure out my next step. i am sure i will come up with more issues/questions.

i really appreciate the time you have taken to help me to this point. sometime i will figure out how to post a dwg. and show you my outcome, if i get there.

[rkent]

one question i do have though is, am i correct that you cannot sweep along a pline that changes elevation?

 

A Polyline will not let you draw in the Z direction. So what you do is rotate the UCS, in this case 45 degrees, and then draw the pline. This way the pline is going up in elevation in the WCS but not in the current UCS. Then you can fillet the corners and finally extrude along that path.

 

now i am going to try to figure out my next step. i am sure i will come up with more issues/questions.

i really appreciate the time you have taken to help me to this point. sometime i will figure out how to post a dwg. and show you my outcome, if i get there.

 

You are welcome. And yes, post what you come up with, I would like to see it.

[tds73]

A Polyline will not let you draw in the Z direction. So what you do is rotate the UCS, in this case 45 degrees, and then draw the pline. This way the pline is going up in elevation in the WCS but not in the current UCS. Then you can fillet the corners and finally extrude along that path.

ahaa. now it is all coming together!

i am just a little slow.

thanks.

[tds73]

well, stuck again. the next step is a little different.i am not usre if 45's are the right choice or not. i will attempt a post of what i have.the green pipe is the one i am working on now. it looks good on the plan view but it needs to angle down and go under white pipe to connect with the 90 degree elbow shown. do i need to take the same steps as required for the 30 inch line? i have tried a lot of things, none seem to get me there.

i could not get dwg small enough to post so i put it in as pdf.

rolling offset-Model.pdf

rolling offset-Model-elevation.pdf

[rkent]

What diameter is the green pipe?

[tds73]

the green pipe is 44"diameter.

so far i have placed a 45 deg. elbow rotated 52 degrees. this aims it down like it is shown on pdf. i believe that this would mean that whatever angle the elbow at the other end has to be, it will need to be rotated the same 52 degrees to get back parallel. i am just trying to figure out what the angle needs to be.

[rkent]

the green pipe is 44"diameter.

so far i have placed a 45 deg. elbow rotated 52 degrees. this aims it down like it is shown on pdf. i believe that this would mean that whatever angle the elbow at the other end has to be, it will need to be rotated the same 52 degrees to get back parallel. i am just trying to figure out what the angle needs to be.

 

For the green pipe I would simply turn 90 degrees in the horizontal, run under the 30", rise 45 degrees, and then roll a 90 degree Ell. See image.

[tzframpton]

AutoCAD MEP does this in like, 2 seconds, for duct and pipe.

[tds73]

sorry for the delay. i was sent to the jobsite to take care of some things.

 

rkent,

i left out some details. it is hard to explain all of the hurdles and make it so someone can visualize it. your solution would be awesome, but i have to run the 44" close to what i have drawn originally. the area this is going is very congested and at the high point there is a walkway that we need to try to leave as open as possible. that is why i cannot go under the 30 pipe until it gets back to the strait that runs parrallel to the floor. so that is how i came up with a plan of running the 44" like the pdf shows. that would send it down at an angle greater than the 30" to get it at the elevation so it would fit under.

It sounded easier at the time, now it is just kicking my butt.

 

StykFace,

i do not have mep, but would it list elbow angle and installation degrees? or would it just draw it as a "model" for show and coordination purposes?also, would it draw it similar to what i have drawn or the model rkent shows?

[tzframpton]

StykFace,

i do not have mep, but would it list elbow angle and installation degrees? or would it just draw it as a "model" for show and coordination purposes?also, would it draw it similar to what i have drawn or the model rkent shows?

Sure it can. That's what it's designed for. Talk to your reseller about an upgrade. You can download the Trial at autodesk.com for 30 days just to test it all out.