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IndustryArena Forum > CAD Software > Rhino 3D > Unwrap a curve?

1. ## 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. ## 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:

3. ## 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. ## 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. ## Re: Unwrap a curve?

I think rhino does have an unwrap command.

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6. ## 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. ## 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).

8. ## 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. ## Re: Unwrap a curve?

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

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.

11. ## Re: Unwrap a curve?

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

12. ## Re: Unwrap a curve?

I understand and good to meet you.

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