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Joining two cylinders at an angle.... what tool?

Discussion in 'Using Alibre Design' started by JST, Jan 11, 2018.

  1. JST

    JST Alibre Super User

    This has always been an issue for me with Alibre.

    If one wants to simply have a cylinder, perhaps representing a piece of pipe, joined at some arbitrary angle to another cylinder, there seem to be remarkably few tools to do that with.

    If the part is rectangular, it is no issue, done in 2 or 3 quick constraint additions. But cylindrical parts have fewer things to "hold to", and thus tend to require more preparatory work. Even the inherent axis etc is not very helpful.

    Of course you can go to the trouble of generating a sweep path, but often you just may want to stick a couple in place as a clearance reference, or you need to have actual cutting lengths for a handrail, etc.

    I have established points on the end faces, but then get constraint errors trying to do something to stick them together.

    Even if you create pre-cut pieces, and assemble, the tools seem to be quite clumsy, and never seem to do what is wanted.

    Just had that, wanted to show 4 pieces of pipe (for clearance checking) that are two parallel lines of piping that turn a 45 degree angle, and it became a major hassle to do without doing a full extrude over a path.

    4 pieces of 2.5" OD pipe, in two parallel lines 10: apart. Each turns a 45 deg angle parallel to the other, and both are 78,25" off the floor.

    I could do an extrude, but there are some different ones and it seems silly to have to do a bunch of extrudes, each for one special case. Should be easier to just have one pipe part that is stuck together as needed to get the pipe shape needed.

    I have had this as a MAJOR hassle doing handrails, with odd angles, welded joints, etc.

    This should be simple, but it never seems to be. Any suggestions?

    Is there any proposed constraint enhancement that would make this easier?
     
    Last edited: Jan 12, 2018
  2. sz0k30

    sz0k30 Senior Member

    I'm glad you got that off yours and my chests :D. Agree 100%
     
  3. Oldbelt

    Oldbelt Senior Member

    Is this what you look for?
     

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  4. JST

    JST Alibre Super User

    Of course, that is what it amounts to.

    But, as I perhaps did not make clear, I have a number of similar situations at various angles.

    Rather than make an individual part for each situation, I prefer to just use a single part that may be used many places. I want to have a part that is a representative length of pipe or cylinder, and join instances of it at the appropriate angle to create the pieces of pipe that must be cleared, etc.

    There really seem to be a very limited number of constraints that work. I have had to make rather elaborate constructions of planes, axes, points, etc to create reference geometry to which the pipes can be aligned. It seems to be a case of always having to "go around the barn the long way", there is apparently no simple and direct method using available constraints.
     
  5. JST

    JST Alibre Super User

    OK, here is an example.

    One floor slab, two pipe pieces (represented by cylinders) that are to be made into a representation of one pipe that turns at an angle.

    The pipe is to be parallel to the floor, 78 inches up, and the two pieces are to join at a 50 degree angle. Because this is only for clearance purposes to other items, there is no need to make or show a real pipe connection, all that is wanted is to get the pipe pieces joined at their ends at the desired angle and height.

    What is the simplest workflow that will make this happen?
     

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  6. DavidJ

    DavidJ Alibre Super User

    If you don't need perfection at the angled joint - it's easy enough. I've modified your assembly.

    Alternatively, you can make a single angled pipe part using thin wall extrude, then put that in your assembly. Change angle in the sketch.
     

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  7. Oldbelt

    Oldbelt Senior Member

    I have made a tube template. TubeTemplate.JPG
    in the editor the wanted angles, dia, length and wall thicknes is entered.
    Then <save as>a new name, not to spoil the tempplate.
    Assembly is made with only 3 constrains. Tubes.JPG
     
    Last edited: Jan 12, 2018
  8. Oldbelt

    Oldbelt Senior Member

    the editor the wanted angles, dia, length and wall thicknes is entered.
    Then save as, not to spoil the tempplate.
    Assembly is made with only 3 constrains
     

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  9. DavidJ

    DavidJ Alibre Super User

    The draft face tool is very handy for generating an angled end on a part.
     
  10. JST

    JST Alibre Super User

    David, the package would not open for me; "unknown error".

    What I actually did was to do an extrude over a path. Then I constrained the result to a plane at the height. To get the bend at the right place, I then had to constrain to the end and centerline, because the bend was not an "entity". If I could have intersected the two pieces, the ends would have been entities.

    I did that because I could not think of another way to do it that did not involve cutting angles etc as oldbelt suggested. That is what I have always done, but it can be very clumsy when trying to find dimensions when you are trying to fit something like a handrail to a space, as opposed to having them all established in a handrail design to begin with.

    I can set the end surfaces at an angle with the angle constraint, but then there is no other constraint that will make them intersect correctly. The ones allowed resulted in constraint errors. I set up points in the center of the ends, which I wanted to make co-incident, but although some constraints were allowed, they all resulted in errors.

    I think SOME sort of extensions to the constraint system are needed to allow intersecting things like this. All methods seem to be clumsy.

    If I want to put a cubical box in a location at an angle, I can DO that easily. But a round pipe or cylinder has far fewer ways to "grab it" for constraints.
     
  11. DavidJ

    DavidJ Alibre Super User

    The package downloaded and opened fine when I just tested it now - maybe try again.

    To grab pipe - show reference geometry.
     
  12. JST

    JST Alibre Super User

    The reference geometry was not helpful, because I simply got errors when using it. It did not seem to be accepted.

    I wanted to set an angle, and to have the center points of the ends coincident. That gave errors, and I gave up. Made the pieces special for each place, and it was simpler than fighting with the constraint system.

    When I do the same thing WITHOUT the rest of the drawing, it will work. Just the two parts. But it is still cumbersome to set up the point with inserted geometry

    Maybe there is an interaction issue.
     
    Last edited: Jan 12, 2018
  13. Oldbelt

    Oldbelt Senior Member

    JST I can't understand what your problem is, I have forwarded a tube Template, in the equeation editor input 5 Data and you have your tube.
    Assembling needs 3 constrains , first tube cut surface to second tube cut surface, 2 reference planes aligned to prevent twist, the 2 center points mated.
    The reference planes and the points is created in the template task.
    Why do you involve a floor and high over it. The building is one item/part and tubing is another part/item
    wich has to be assembled in and constrained, this is only an advice because appertlig you is a newby.
     

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  14. JST

    JST Alibre Super User

    Well, I have been using Alibre for a number of years, and being paid for it, but this has been a continuing issue. You probably cannot truly understand it unless you have to design things to fit in a poorly defined space, and so you have in some cases to get the dimensions from the model instead of making the model to pre-determined dimensions.

    Why the floor? Because it is there, of course. I just needed to check clearances from portions of a large and complex model to pipes that were not included in the original model, for which I had dimensions expressed as distances from them to parts OF the model.

    Three are several, and I checked the first one...... So I put in one section, and went to put in the next at the correct angle, and the pieces would not accept the constraints to connect them.

    The model is way too big to include. here it is with one set of pipes. There are more. Made these as path extrudes, when the simpler way did not work. Some parts are too detailed, but they were already there, and it helps folks understand what they are seeing.
    TS-1 lower level trial layout 17.jpg
     
    Last edited: Jan 12, 2018
  15. HaroldL

    HaroldL Alibre Super User

    I had no problem constraining the pipes in place - the only thing missing in your description is the spacing between the two pipes.
    I think that if you constructed the dummy pipes with planes and axes at both ends it may give you the features (planes and axes) needed to stack the pipes end-to-end.
    pipes.png

    I made a pipe with planes and axes at both ends so you don't have to be concerned about which way the pipe is oriented when inserted into an assembly. You can also build from each end as the need arises. The axes are parallel to the planes but you could add planes and axes at 45 degrees if needed.
     

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  16. JST

    JST Alibre Super User

    Well, it worked for me in isolation to constrain the end surfaces 45 deg and mate or align points I put on axis and in the end plane. I tried that after I did the path extruded pieces I used.

    For some reason it did not want to work done the same way when in the big model. I had planned to just use the same two, changing the angle etc for the different places, since I do not actually need them to be in the model. But it did not work done that way except in isolation.

    More Alibre oddity? Or a model fault? Who knows what evil lurks in the heart of the model (or Alibre)?
     
  17. ajayre

    ajayre Senior Member

  18. Oldbelt

    Oldbelt Senior Member

    Sorry I have no intension to offent you. I do have designed things in poorly defined spaces as you call it.
    Every time you design complex Machinery or "Consumer" products, as I have for 47 years, you have to go forth and back in the design proces.
    Thats is easy now a dayes because we have parametric design tools as Alibre.
     

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  19. HaroldL

    HaroldL Alibre Super User

    JST,
    I think part of the "trick" is to use as few constraints as possible or at least ones that don't need a lot of "figuring out" to resolve.
    I reworked your pipe and floor assembly, this time with the pipe I created with the extra planes and axes at both ends. I only used thee constraints between each pair of pipes - a Mate between two axes to act as the pivot axle, a Mate between two planes that are perpendicular to the pivot axes, and an Angle between twp planes that are parallel to the pivot axes.
    You do need at least three offset mates to position the first pipe in the group. The second set of pipe only need a mate between the pivot axes and a mate to align the planes that are perpendicular to the pivot axes. From there I inserted an offset mate between each pair of pipes that are offset and parallel to each other, the angle will fall into line on the second pipe.

    In this image I marked the steps I took and only show the reference geometry for one of the pipes since it gets a little crowded with both pipes set to display them. But hopefully this will help to explain the process I used.

    pipe constraints.png

    This is a screen shot saved out of Alibre...

    pipes and floor assembly.png

    And finally, here is the pipe and floor assy using the new pipes with reference geometry.
     

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  20. JST

    JST Alibre Super User

    Oldbelt: Not offended at all.

    I agree, it is a back and forth process. My example was "detailing" poorly described pipe handrails that simple have a few general dimensions and must otherwise be "fitted". Often they are at odd angles on stairs.

    My experience is that it takes as long to detail those handrails as it does to detail the entire roof and floor structure. This is partly due to the difference in available direct tools that can be used for "cartesian co-ordinate" tasks vs angles, especially with cylindrical parts.

    I would like to see some fixing of and expansion of the constraints to facilitate this. Some constraints that appear to be good, also seem to put restrictions on how the parts will move and align even though there really is NOT such a restriction in reality.

    One case is the tangents, which seem to freeze some unrelated movements, and lead to constraint failures. "Not consistent for unknown reason" is a common error message in those cases, and it is not "real", meaning that if you can manage to move the parts closer to what you want, the new constraint may work.

    Unfortunately, one may have to REMOVE one or more constraints before Alibre will allow the needed moves, even though the moves are actually allowed by the existing constraints. And then careful application may be required to avoid the parts going back to the "inconsistent" position, or having a different error pop up.

    Another issue is that construction geometry cannot be made part of the part, so that it shows up when making assemblies. Having that would be a help also.
     

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