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Midpoints in bends on a tube

bigblue97mustang
Hello all. I was wondering if anyone could explain how to get some of these points in this drawing, and hopefully help in getting a dimension.

For this part, I would create a plane on the left end of the part, followed by cylinders for each straight. Then a plane on the right side. Next, I would construct a pierce point for plane 1 and cylinder 1 which would give me midpoint 1. Then construct an intersection point between cylinder 1 and 2, and that would be midpoint 2. I would continue this for the rest of the tube until i get to the last pierce point giving me midpoint 7. I have learned that i can create a cast point on cylinder 2, and it will give me midpoint 2.2; however, I have not yet been able to figure out a way of getting any of the x.1 midpoints.

That is where my question starts: How can i get these .1 midpoints? I feel like I've tried every combination of picking two cylinders and all the different types of points, and have had no luck in getting them. I have XYZ coordinates for these points, but more importantly, i have length-of-straights dimensions that are taken as a measurement between for example 1 to 2.1. This is a crucial measurement to the fit/form/function of our part, and as of now, i have absolutely no way of checking it.

My second question is this: Almost every part we have has a dimension for mid 1 to mid 7 across the Y-axis (as shown). But they will also dimension in this case, the top of cylinder 1 to the bottom of cylinder 7 (relative to the Y-axis) across the Y-axis. Every time i try to measure Cyl 1 to Cyl 2 across the Y-axis (with plus diameter getting me the closest), I never can seem to quite get a passable measurement.

Any help in either of these matters would be greatly appreciated.
  • The image is too small to see which points are what. Are the .1 points at the start/end of the cylinders? There's no way you can measure that, as I see it. It should be possible to construct them with the following method, though (under certain assumptions).

    Create a plane of point 1, 2, 3 (red in the picture)
    Level to that plane
    Construct a circle, tangent to two lines (1-2 and 2-3), with a fixed diameter = 2 x Bend radius,
    Construct points (green) as tangent of line and circle.


    But I may have misunderstood you completely...
  • Yes, I wish there was a way to upload a larger photo on here. Basically:

    2.1 Would be the location of where the first straight ends/first bend begins
    2 Would be the mid-point (intersection) of the bend between the first and second straight
    2.2 Would be the end of the bend/beginning of the second straight.

    Typically, i can get 2.2 by creating a cast point on the second straight cylinder, but I can't figure out how to get 2.1

    And, honestly, your explanation made no sense to me unfortunately. No, i do not need to measure them, and I don't believe i can be accurate enough to determine where the straight ends, and where the bend begins consistently. That is why i typically use the cast points.
  • Hopefully this one shows up better
    Attached Files
  • Ok, then I understood you correctly. Don't trust the cast point unless you have clicked an autocylinder on CAD. If it's a measured cylinder you will never measure at the exact start/end, and if you don't have CAD where would you get the numbers from?

    I'm sorry that my explanation was difficult - could you specify more clearly what you don't understand?

    The red points in my picture are your intersection points 1, 2 and 3. The two green Points are your 2.1 and 2.2 points. They are the tangent points between the center lines and a nominal circle with the bend radius.

    You'll have to repeat with 2-3-4, 3-4-5, 4-5-6 and 5-6-7 to get all your Points


    It is also possible to calculate the rotation by comparing plane 1-2-3 with plane 2-3-4 and so on.
  • Alright, so I am building my program with a cad. I'm not 100% sure if im doing a measured cylinder or an auto, but I build by shift-left clicking my features on my cad.

    So here we go for explaining:

    If i measure 2 seprate planes on two cylinders, i dont see how i can ensure they are not twisted in relation to eachother.

    I imagine the point you had in the middle is an intersection point of those two planes?

    I dont understand how to construct tangents, as i didnt see any such options in the auto circle/construct circle options.

    Lastly, this will only provide me points on the outside/inside of the bend of the bent cylinder. The point i need would be the centroid.
  • I did try to do this method, which of course didn't work for me.

    constructed cylinder 1

    constructed cylinder 2

    constructed a torus in between the two

    Was hoping i could construct an intersection point of some sort, or even better, an intersecting circle (then create a mid point of that circle)

    But for one reason or many, it said math failed for both a circle and point when i chose a cylinder and torus as my features.
  • No, my method works on the centre line. The points 1, 2 and 3 in my picture are the first three centre line's intersection points, the two green points are the 'inflexion points' where the centre line passes over into an arc, and then to the next centre line.

    You need lines and an alignment to be able to construct the tangent circles and tangent points, so if you already have cylinders, you must create (cast) lines from all of them.
    Then you construct a plane from your intersection points 1, 2 and 3, and level to that (this is the plane the first bend is made in)
    Now construct a circle tangent to lines 1-2 and 2-3, with the fixed bend radius



    Then construct a pierce point from lin 1-2 and the circle (this is your point 2.1) - this is the single intersection (==tangent point) between line 1-2 and the circle, as the circle was constructed as tangenting the line
    Then construct a pierce point from lin 2-3 and the circle (this is your point 2.2)





    ...and repeat
  • Dang cool man, that got me a whole lot closer to understanding it. I have a few questions though:

    It would seem to me, that assuming i have an alignment already, it seems unnecessary to construct planes out of my midpoints (gotten from the intersection between the cylinders) to use for the circle. However, if it IS necessary, can you explain that in a little more detail please? I've never constructed a plane before, always a shift-left click on cad, or probed it out on the physical part. Lastly, for this part of the question, can you detail what my alignment would look like. You said level to that, what is that exactly? The first plane?

    The pierce point parts of this process, i very much understand, and now I see what you meant in your origional picture. The lines you had labeled planes were achieved from the midpoint on either side of the cylinder (Or as a cast line based off that tube). Which would be the more accurate/reliable? Using the midpoints or the cast line to construct the plane?

    Secondly, Considering i am creating a 2-d feature, would i be correct in thinking i need to be in a workplane looking DOWN at the circle, in a way similar to as if i was looking at your first picture?

    Thank you SO much for your very detailed steps. I am still very new at this, and you are quite good at explaining this in a way i can understand!
  • Visualize the two cylinders's centerline never actually intersecting.... therefore construct a plane with the cylinders endpoints (the red points in Andersl's example) and attempt your method again. Use 3 points if possible, 2 end points from 1 cylinder and 1 end point from the other.

    EDIT: Never mind I posted this too late... good explanation as usual
  • So, here's where I'm at with this so far:

    I have two cylinders constructed with a plane on either side, and a bend in the middle.

    A pierce point on the plane-cylinder ends, and an intersection point in the middle.

    I constructed a plane from pierce point 1 to midpoint, then another plane from midpoint to the second pierce point.

    Changed to workplane Z (which puts me looking down on the angle, similar to Anders first picture)

    Constructed tangent 2-line circle, selecting the 2 theoretical planes.

    Changed theoretical diameter to 240 (didn't change XYZ values)

    Clicked OK, and it formed the circle around my XYZ origin.

    Is this because i didn't do the level step you told me about, or is it because i didn't put my XYZ values for the midpoint itself? (And if i do change the XYZ theos, will it still adjust itself accordingly if my midpoint actual coordinates change, or does it lock this feature to that exact location, regardless of what else changes?)

    And, thank you anyways Dude, I know you're just trying to help!
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