How to determine an unknown radius or diameter

By thewelder (***)

Date 03-26-2009 06:46

Thank you SR. is usefull and simple.

By aevald

Date 03-26-2009 07:41

Hello Jaime, I had also included another attachment to show how to figure out the radius from the outside as well as the inside, unfortunately I couldn't manage to get it to load properly. So stay tuned, when I get it right I'll add that too. Best regards, Allan

By thewelder (***)

Date 03-27-2009 05:25

Thank you. I'll be here.

By Superflux (****)

Date 03-27-2009 06:48

Allan,
Thanks for that Trig review. I've had to solve these problems with some less acurate and more "creative" methods.
Unfortunately, I somehow managed to pass Trig with a "B" under the influence of "herbal study aids"! The '70's were hard on my short and long-term memory.
Saved this one on my desktop for future reference.

By Joe Davidson (**)

Date 03-27-2009 13:40 Edited 03-27-2009 13:44

Hey Allen great info, wish I knew this trick last summer. I printed this out and put it in my truck. I have a question that maybe you can help with. On a pipeline job last summer I was working for a small company who didn't want to spend money on an engineer to figure out bends we had in 16" and 24" pipe. Instead the boss guessed on the degree and radius of the bends. He had to send pipe to bending shop 3 times before he got it right. Would using this method work to figure the radius of a bend in pipe? Also, do you or anyone else have a method for figuring the angle of a bend?

By aevald

Date 03-27-2009 17:09

Hello Joe, to hopefully answer some of your other questions I have included another sketch. This sketch will allow you to determine the outside radius of an elbow, the centerline radius, or the inside radius providing you have a full 90 degree elbow to work with.

By aevald

Date 03-27-2009 18:48 Edited 03-27-2009 19:59

Hello again Joe, I don't know for sure if this is more along the lines of your question but here are some additional examples that might be of some help. Best regards, Allan

By Joe Davidson (**)

Date 03-27-2009 20:03

Thanks again, that second one was what I was after. When they bend a 40' pipe they leave straight sections on each end. So if I pulled a string line from each straight end and keeping the string lined up on the center line of the straight ends, can I find the degree of the bend using that method?

By aevald

Date 03-27-2009 21:35

Hello Joe, here's an attempt to possibly show how you could do that. Best regards, Allan

By Joe Davidson (**)

Date 03-27-2009 23:35

That's even better. Exactly what I was talking about. Thanks, Going to put this one in my book too.

By gndchuck (**)

Date 03-27-2009 22:51

I've used a similar method, but your's is a whole lot better than the one that I've been using. As always thanks for the information, if I ever find where my teaching aids got off to in the new shop, I'll post some pictures.

Charles Welch

By aevald

Date 03-27-2009 23:36

Hello Charles, I will look forward to those and hope you are successful in finding them sometimes. I also hope others will include other different examples of their techniques. I know they're out there. Best regards, Allan

By thewelder (***)

Date 03-30-2009 05:11

THANK YOU Sr. all info is very helpfull.

By thomasyyz (**)

Date 04-11-2009 19:42

Allan don't trust a square with bent pipe, measure out from the vertex one metre in both dirrections and then measure the distance from these two points.
Be carefull with your pipe diameters (6" pipe is 6.65" O.D.), now can you explain to me the formula of a "rolling offset"; if I need to displace my 6" pipe, 8" (E/W) to find an axis which is up and down, using a standard elbow joint with a 9" advance how many degrees would I need to cut the other elbowjoint. I usually do this with a compass but I would like to be able to do this on paper. Wish I was in a position to help with your students, they are very lucky to have someone who has the insight on both the practical and theoretical side of the trade.

By aevald

Date 04-12-2009 06:23

Hello Thomas, thanks for commenting and asking some other questions. I am currently home and not able to access some of my resources, however, I will certainly try to come up with some comments to possibly address your questions. I believe I also understand your comment regarding the "1 meter from the vertex either direction and then measuring across these points". Using a modified formula for determining chord dimension I believe I could readily determine the angle, thus your suggestion makes terrific sense. I will also try to come up with a sketch to illustrate this. When I do, you can possibly tell me if this is what you meant. As to your rolling offset question, I am not a pipefitter by trade so I am not well versed on many of the terms used within this sector of the trades. I believe I do understand your question here, so I will try to make comment and also include some sketches to address this as well. Thanks for posting and best regards, Allan

By aevald

Date 04-14-2009 06:14

Hello Thomas, since I am an American I don't readily use the metric system so please bear with me while I try to illustrate the example I believe you were referring to. Instead of using 1 meter I have substituted 36" for that dimension. Extending 36" either direction from the vertex I make two marks, then I measure the distance between these two points and come up with 65 1/4". The triangle represented by the two 36" dimensions and the the 65 1/4" dimension represents two right triangles that are oriented back-to-back. I use the 36" dimension and half of the 65 1/4" dimension to represent two of the three dimensions for one of the right triangles. Using pythagorean theorem I can solve for the missing side of the right triangle and come up with a dimension of 15 3/16". Using 15 3/16" to represent "rise" and 36" to represent "run" I can use a right angle trig function to solve for lesser angle in the triangle. rise(15 3/16") divided by run(36"), inverse tangent will yield 25 degrees. Since a triangle contains a total of 180 degrees I can subtract the 25 degrees and the 90 degrees to determine the last angle of 65 degrees. When you have the two right triangles oriented back-to-back the sum of their angles equals 130 degrees. When you look at how these two triangles are oriented in the sketch that I have included you can see how you subtract this angle from 180 to determine the actual angle that the pipe is bent. I hope you can figure out my gibberish where it applies to the sketch that I have included.
I also have some other information to include for you in regard to your other question. I haven't quite got it compiled,so I will include it a bit later. Best regards, Allan

By thomasyyz (**)

Date 04-14-2009 16:58

I followed along perfectly, been some time since I've worked using the Imperial system, but it is more simple to understand looking at it through metric.
Try to understand that being American does not mean that you are born in the U.S. of A. for other people. I'm Canadian as well as being American, and the Metric system I've had to chew since 1977.
If I was to offer any advice to your students tell them that the math is the most important, and the formula or equation of a rolling offset, displacement of axis are very hard to dominate when they are compounded. Measure twice, cut once(can you see it¿!?).
The best lesson I've learned, cut when you see it!!
if not broom :)

By aevald

Date 04-16-2009 15:24

Hello again Thomas, I finally got the time to work on the rolling offset some. I have included my information in another post about rolling offsets. So if you're interested you'll find it there. Have a great day and best regards, Allan

By Cumminsguy71 (*****)

Date 06-11-2009 23:28

Allan, your making my brain hurt......:-)

Good info though!

By raftergwelding (*****)

Date 06-13-2009 21:54

WOW thats just mind boggeling guess i should of taking more than just basic math in high school. i barely passed intro to algerbra and now theres trig. involved i'm stumped

By aevald

Date 06-14-2009 00:02

Hello Shad, don't let this sort of thing make your brain hurt. I wasn't a great math whiz in high school, but when I got into the fabrication end of the trades I did see the value of certain mathematics, that is: "APPLIED MATHEMATICS". Helped me immensely to come to understand the value of certain aspects of math. I still don't do well with algebra, but I'm pretty comfortable with right angle trig. and other functions that I can relate to fabrication. Anymore, I try to take note of any methods that will help with accuracy or make it easier for me to accomplish the work that I am trying to do. That could mean an application of math or it could mean some sort of "trick of the trade" that I can pick-up from anyone who is willing to share their skills and tricks. Good to hear from you and take care, Allan

By Cumminsguy71 (*****)

Date 06-14-2009 12:09

I'm with you shad, all I had was basic math and never did care for it as a mechanic. Once I started building the stairs, hello pythagorean theorem and a host of other math. It's amazing though, the formula stuck with me, as Allan said "Applied Math". Mostly it's because it made math exciting(no, really), to figure out the length of the stringers and other things. In this respect it was applied to something I was interested in not just getting it beat in my head, bored in a classroom talking about two trains on going 55 and so on.

I actually read about the pythagorean theorem in a book, but it did'nt stick. It took actually getting out there and taking real measurments, using the calculator for it to finally take hold with me.