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Thread: Pipe fitting - bend radius

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    Default Pipe fitting - bend radius

    Can someone please shed some light on an issue for me.

    Working with Revit MEP, I am creating new pipe fittings and have come stuck on one parameter (how to obtain or how to calculate it)

    On a fitting that has a bend (an elbow say) where that bend is governed by a “Centre Radius” parameter to keep the bend consistent when the fitting is used on various sizes of pipes and at various angles. This “Centre Radius” parameter is governed by values that are obtained from the lookup table for the fitting but I can’t find how to calculate this value to put it into a lookup table in the first place. I am trying to create a new fitting and lookup table for a new pipe type, the MEP tutorial gives you the "Centre Radius" distance and it gives you the lookup table with all the values already entered for each pipe size, but doesn’t actually tell you how to calculate it for new pipe sizes. I have also tried using an existing fitting and lookup table that I can re-name, but I want to add a few more sizes to the lookup table but I can’t find that one measurement or how to calculate it, I have tried to work out how they did the existing ones but can’t seem to crack it. This measurement is integral for the bend to perform properly, if it is done incorrectly the bend will still get inserted when you draw two pipes at an angle but the centre part of the fitting, the bend between the two couplings, gets omitted and of course the pipe fitting then doesn’t look right.

    I was hoping that someone out there, with more MEP experience than me, was able to explain to me how I calculate this value so that I can put it into the lookup table for new pipe sizes.

    Any assistance would really be appreciated.

    Thanks

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    Default Re: Pipe fitting - bend radius

    I believe the Autodesk Family Guide has a pretty good tutorial on creating a pipe elbow that may help.
    Not sure if I'm allowed to post a link here, so go to the autodesk wikihelp and search for The Family Guide.
    wikihelp.autodesk dot com
    Last edited by mvalencia25; 2013-01-30 at 02:51 PM.
    Miguel Valencia, LEED® AP BD+C
    CAD/BIM Coordinator
    Syska Hennessy Group, Inc.

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    Default Re: Pipe fitting - bend radius

    Hi Miguel

    That was my first port of call, but as I said in the original post the tutorial gives you all of this information it doesn't actually show you how to create the lookup table or where you would get the information from to enter into the lookup table or how you work out this bend radius if you wanted to add some more sizes to a current lookup table. As I said, I can get all the other information except for the bend radius of the fitting. Thanks for your time though.

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    Default Re: Pipe fitting - bend radius

    I assume that you are talking about the Inside and Outside diameters as well. Those are based on pipe material and the sizes can be found @ http://www.engineeringtoolbox.com/. Also, attached in a PDF of one of our elbows. Hope this helps.


    Pipe Elbow.pdf

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    Default Re: Pipe fitting - bend radius

    Hi Swartzie

    No, I need to find out how to work out the radius of the bend, I have the ID and the OD from the manufacturer. In your PDF document it would be the "Centre Radius". Your example is easy to calculate as it a simple 90° bend with no couplings where that radius centre point is squared to each end, but I am talking about creating a bend with a longer curve that doesn't meet up nicely at a centre point like your example. I am trying to find out how to calculate this centre point for various pipe thicknesses.

    Thanks
    Des

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    Default Re: Pipe fitting - bend radius

    So in the attached screenshot:

    If you're referring to the "Sweep Radius" (as I have mine named) the value can be fairly simple. It will vary depending on your fitting - a PVC bend will differ than a Long Sweep. I wanted to do away with lookup tables completely from my fittings so I took the OOTB fittings, recorded the radius values for each pipe size, and then created a simple formula that mimics what the lookup table did.

    If you're talking about the "Sweep Offset" that controls the center of the sweep (This is necessary to keep the connectors projected intersection at the origin of the family. If you don't do this the fitting doesn't work when connecting pipes), then the formula is "Sweep Radius * tan(Angle / 2)".

    Hopefully that helps. Fittings are some of the most finicky and difficult Revit families to create...

    Bend Parameters.PNG

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