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IndustryArena Forum > CAD Software > Rhino 3D > Unwrap a curve?
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  1. #1
    Join Date
    Nov 2009
    Posts
    50

    Unwrap a curve?

    I built a tube cutter attachment out of the headstock of 9x20 lathe for my CNC plasma cutter. I can cope pipe with it all day long. I know there's a coping calculator on the internet and I've used it to create flat curves for this sort of thing. But what I want to do is cut a piece of pipe that will be welded to a flat surface at a given angle. In other words, think of a flag pole or something of the sort that is pitched 60 degrees to the left and 15 degrees to the front. I can project a straight line on the pipe and I get the curve, but is there a way to unwrap it?

    I kind of understand the tube calculator suggesting a 1" offset on 1" pipe and getting a miter cut, but that seems like you would only get one angle. I want a compound miter. I could cut it on the chop saw, but I'd have to set the piece in the saw at 60 degrees and then lift the pipe 15 degrees and somehow gig that to get it right every time. I want to put the pipe on plasma table, spin it, cut it, done.

    Is there a way to get this done in Rhino or something else?

    Attachment 243328

  2. #2
    Join Date
    Dec 2008
    Posts
    4548

    Re: Unwrap a curve?

    I don't think your looking to "unwrap a curve". Essentially, that's just the length of the entity. You wont really have "2 angles". Cutting a pipe at an angle will essentially just be an ellipse, correct? So you would have a single angle cut, then rotate the part on it's axis to get the other angle.

    There's probably some complex math formula to get the angle of the cut, but here's how I would do it. Use a solid cylinder and rotate it by the 2 values you have (60 degree's to the side then 15 forward)

    Now Boolean diff the cylinder with a plane and delete half of it. Now set and rotate the cut cylinder so it is sitting flat and perp in the x and y planes again. This will give you a simple angle cut to make on a pipe.

    Now setting it flat on that cut will give "some" angle to the pipe. Rotating/pivoting it's placement will generate the 60/15 angle you want... the welder will be responsible for the exact degree...

    Here's an iges file:
    Attached Files Attached Files

  3. #3
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    Dec 2008
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    4548

    Re: Unwrap a curve?

    As a second thought, I don't think that this will get the proper angle you are looking for. Rotating the cylinder to 60 degree's "THEN" rotating the forward 15 will change the 60 angle.

    It "IS" a way to get the angle you need for the 2d cut, but I think you need to follow up on the math formula to get the cylinder rotated properly to produce the 60/15 your looking for. Probably a trig function.

  4. #4
    Join Date
    Dec 2008
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    4548

    Re: Unwrap a curve?

    Ok so the brain wasn't working and I asked for some help on it in another forum. Got a great suggestion to get the proper angle.

    You'll want to draw the 2 lines in the respective views at the 60 and 15 rotation values, and extrude them into surfaces, then create and intersection curve from the 2 surfaces. You can then create a cylinder off of that intersection curve using the line as the normal extrusion direction (or as suggested, use a cplane with a new z axis matching the intersection curve). Then cut that cylinder with the world origin xy plane.... This gives the cylinder angle that can be cut with a straight line on your laser (whatever)

    Another thing you may want to setup on the model is a "centerline" which can be matched on the actual cut pipe. So whoever is laying it out after the cut can easily find the rotation of the pipe that will generate the 60/15 you are looking for....

  5. #5
    Join Date
    Jul 2010
    Posts
    46

    Re: Unwrap a curve?

    I think rhino does have an unwrap command.


    Sent from my iPad using Tapatalk

  6. #6
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    Dec 2008
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    4548

    Re: Unwrap a curve?

    so after considering this more I realized I gave you two answers and both could be correct, depending on what's your result is that u want. the first method gives you your Pole with a correct 60 degree and 15 degree rotation like you asked for however its projected angle will be incorrect. the second method gives you a 60 degree and 15 degree angle from a projected perspective. I guess it just depends on what you were after.

  7. #7

    Re: Unwrap a curve?

    For simple surfaces/solids the command to use: UnrollSrf (example pictured below).
    For complex surfaces/solids: Smash (smash may provide inaccuracies and should be avoided for manufacturing).

    Click image for larger version. 

Name:	unroll_dev_srf.png 
Views:	2 
Size:	438.2 KB 
ID:	243544

  8. #8
    Join Date
    Dec 2008
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    4548

    Re: Unwrap a curve?

    Hi jason.
    That would be a command to use if he was cutting sheet metal then rolling it up into a tube, or using a 4th axis where the tool was stationary and the pipe was rotating for the cut. I think he wants to lay a pipe flat on a table and cut a diagonal that will lean the pipe....

  9. #9
    Join Date
    Jul 2003
    Posts
    1220

    Re: Unwrap a curve?

    Not 100% sure but I think compound angle is = square ((60 X 60) + (15 X 15))

  10. #10

    Re: Unwrap a curve?

    ^?
    Situation: aaronbee has a CNC cutter with a rotary headstock and the coping calculator he wished to use doesn't compute flat curves beyond a single angle.
    Task at Hand: Provide a method in developing the flat curve for coping a 60° and 15° combined.

    The image below represents the flat line, (blue), for a 1" paper thin tube with the 60° and 15° combined. The line's arch will increase as the tube's wall thickness increases.

    Click image for larger version. 

Name:	unroll_flat_curve.png 
Views:	0 
Size:	126.3 KB 
ID:	243618

  11. #11
    Join Date
    Dec 2008
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    4548

    Re: Unwrap a curve?

    Jason forbes i believe you are correct. He DOES want the rotary path.

    My bad....

  12. #12

    Re: Unwrap a curve?

    I understand and good to meet you.

  13. #13
    Join Date
    Jul 2003
    Posts
    1220

    Re: Unwrap a curve?

    Quote Originally Posted by Kiwi View Post
    Not 100% sure but I think compound angle is = square ((60 X 60) + (15 X 15))
    Compound Angle for 60 and 15 deg is 60.293 deg

    CAngle = Atan(Sqr(Tan(60) ^ 2 + Tan(15) ^ 2))

    Code for 60.293 deg
    Diameter 25.4 mm.
    G01 X-0 A0
    G01 X-0.3382 A10
    G01 X-1.3424 A20
    G01 X-2.9821 A30
    G01 X-5.2075 A40
    G01 X-7.9511 A50
    G01 X-11.1294 A60
    G01 X-14.6458 A70
    G01 X-18.3935 A80
    G01 X-22.2587 A90
    G01 X-26.1239 A100
    G01 X-29.8716 A110
    G01 X-33.3881 A120
    G01 X-36.5663 A130
    G01 X-39.3099 A140
    G01 X-41.5353 A150
    G01 X-43.1751 A160
    G01 X-44.1793 A170
    G01 X-44.5174 A180
    G01 X-44.1793 A190
    G01 X-43.1751 A200
    G01 X-41.5353 A210
    G01 X-39.3099 A220
    G01 X-36.5663 A230
    G01 X-33.3881 A240
    G01 X-29.8716 A250
    G01 X-26.1239 A260
    G01 X-22.2587 A270
    G01 X-18.3935 A280
    G01 X-14.6458 A290
    G01 X-11.1294 A300
    G01 X-7.9511 A310
    G01 X-5.2075 A320
    G01 X-2.9821 A330
    G01 X-1.3424 A340
    G01 X-0.3382 A350
    G01 X-0 A360

  14. #14
    Join Date
    Jul 2003
    Posts
    1220

    Re: Unwrap a curve?

    Quote Originally Posted by Jason Forbes View Post
    ^?
    Unsure what this refers to


    Quote Originally Posted by Jason Forbes View Post
    ....The image below represents the flat line, (blue), for a 1" paper thin tube with the 60° and 15° combined. The line's arch will increase as the tube's wall thickness increases.

    Click image for larger version. 

Name:	unroll_flat_curve.png 
Views:	0 
Size:	126.3 KB 
ID:	243618
    What angle did you calculate for the flat?
    Also why will the arch change if the wall thickness is increased?

  15. #15

    Re: Unwrap a curve?

    The angle was produced with the model pictured below (UP, 60°, 15°).

    This project requires a swarf tool-path to create a flat pipe surface for mounting at the 60°/15° angle. I assume the machine used for this project is not capable of swarfing and will require additional planning to produce a cut that precisely mates a surface at the 60°/15° angle. A swarf tool-path will stay the same as the pipe thickness changes. A contour tool-path will need adjustment for every pipe thickness change. The image below displays the 60°/15° face with a 0.1200" pipe thickness (highlighted in yellow).

    Attachment 244212

  16. #16
    Join Date
    Jul 2003
    Posts
    1220

    Re: Unwrap a curve?

    That's interesting software.
    What is the angle of the flat face the software shows?

  17. #17

    Re: Unwrap a curve?

    The measurement is 28.8791248°. That amount of precision is highly unlikely, use the value with caution.

  18. #18
    Join Date
    Jul 2003
    Posts
    1220

    Re: Unwrap a curve?

    Quote Originally Posted by Jason Forbes View Post
    The measurement is 28.8791248°. That amount of precision is highly unlikely, use the value with caution.
    That angle is the result when the tube is rotated 60 deg and 15 deg and is not correct as BurrMan points out in #3
    The angle should be 29.7075 deg.

    Quote Originally Posted by BurrMan View Post
    As a second thought, I don't think that this will get the proper angle you are looking for. Rotating the cylinder to 60 degree's "THEN" rotating the forward 15 will change the 60 angle...

  19. #19

    Re: Unwrap a curve?

    I don't understand.

    aaronbee wrote,"...think of a flag pole or something of the sort that is pitched 60 degrees to the left and 15 degrees to the front. I can project a straight line on the pipe and I get the curve, but is there a way to unwrap it?"

    My impression is that aaronbee needed assistance in a method of unwrapping a curve for his project. That may have been accomplished. What project are we working on now?

  20. #20
    Join Date
    Dec 2008
    Posts
    4548

    Re: Unwrap a curve?

    Quote Originally Posted by Kiwi View Post
    That angle is the result when the tube is rotated 60 deg and 15 deg and is not correct as BurrMan points out in #3
    The angle should be 29.7075 deg.
    I think what I pointed out was that there are a couple different results, depending on what was requested. But both are correct...

    There is also the "projected angles" of 60 and 15, which are different than rotating a cylinder 60 and 15 degrees....

    I had also missed in the original request that he actually was using a rotary, so the unrollsrf will get the curve he wants for a 4th axis wrap. But, how you cut the initial cylinder seems to be what's being discussed now....

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