Developing a wrap-around pattern from cross section view

[Quik&Easy]

Gentlemen, I find myself in need of some help. Attached is a simple drawing of a round tube sitting on an imaginary level grade. I'm needing to develop a pattern to cut the bottom angle. I'm making a scale model and this is one of the elements. The scale is 1"= 10.66" so this round tube will be 4.5" in diameter. The angle is too gentle to cut in my horizontal band saw; can't fit it between the guides. Years ago, we used to grid out from a base line and develop a continuous curved line on flexible linoleum that when wrapped around the tube, would allow a line to be drawn on what would be my grade level line. We would then cut the steel tube with a torch on said line. Did this for 24" to 90" diameter pipes. I need to do this for this one cut; I think I can get all the rest of the angles for the project on the saw. I'm hoping that the printable (can be done on more than one sheet if needed and taped together or something) paper pattern can be rendered easily, such as a sheet metal shop might develop a flat pattern for rolling or bending. I'm limited to legal size paper, 8.5 x 17". I'm using AC LT 2011 so I'm limited in my abilities. I'd appreciate any help.

 

Thanks!

Ken

tube angles_number2_.dwg

[steven-g]

OK here is my take on it, I used a series of straight lines, you could create a spline from the points. To the best of my ability this should give you a 4.5" diameter tube. And it was also done with Autocad 2011 LT

tube angles_number3_.dwg

[Quik&Easy]

That looks very much like what I was looking for, thank you! I'll try it tomorrow with good luck. Is there an easy explanation as to how you arrived at this? I'd be interested to attempt to duplicate it at some point. I may have need for this process again in the near future if the last couple angles won't fit in the saw. Ken

[paulmcz]

Steven, shouldn't the curve be symmetrical?

tube angles_number4_.dwg

[gazza_au]

See attached, my program is metric so i take it your 4.5" tube o.d would be the equivalent of 4" pipe 114.3mm o/d,I'm sure you can work it in to sheet sizes and scale it from here for printing a wrap around.

tube angles_number4.dwg

[paulmcz]

Here is a graphical solution for your next case

pipecuttemplate.dwg

[steven-g]

Steven, shouldn't the curve be symmetrical?

Yeah I just checked it, and somehow had started just off centre (if you can have a centre of a circle) but the outline should be good.

 

EDIT - drawing added (centred).

tube angles_number3_(2).dwg

Edited October 30, 2013 by steven-g

[Quik&Easy]

Gents, thank you for the solutions. The answers will be helpful to me now and in the future. I think these responses will work just fine!

 

Paul, in your graphic, the 30 divisions; theoretically, would choosing more increase the accuracy and smooth the curve on larger diameter stuff or is 30 chosen for a specific reason?

Gazza-au, the tube I'm using is DOM tubing, 4.5" diameter, .120 wall, but yes, 4" pipe does seem to have the same OD, just the heavier wall.

 

Thinking back on it, we did the linoleum trick around 1980-82.........no wonder I'd forgotten how!

[paulmcz]

Paul, in your graphic, the 30 divisions; theoretically, would choosing more increase the accuracy and smooth the curve on larger diameter stuff or is 30 chosen for a specific reason?

 

No, no specific reason. Any number will do. As you say, greater the number, smoother the curve.

[Quik&Easy]

Success! Printed on 2 sheets, knitted them together, checked some reference measurements and seems to work like a charm. This has saved me quite a bit of time and I thank you all.

Ken

[paulmcz]

If you have an access to full, non LT AutoCAD, you can download a lisp routine I posted here some time ago. It does exactly what you need but it is about 100 times faster than any manual method

[Quik&Easy]

Most of my work, probably 98% or so, is very straightforward and handled nicely be the LT version. Cost is a consideration, too.