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can't close a sketch profile using a spline

IsoThermIsoTherm Member Posts: 66 PRO
greetings,
I have four splines. One makes a simple two point spline curve, the second is it's offset. The remaining two are 3 point splines enclosing the ends of the of the first two. I'm having a hard time getting one of the end splines to close for a profile. I use the coincident constraint when I start and end the spline, and the constraints show when I turn them on, but if I zoom way in on the ends f the spline, I can see that it's not actually coincident. What's going on? The enclosure spline on the top end seemed to work this time but I've been struggling with it in several sketches.









thanks
Isotherm

Answers

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    steve_shubinsteve_shubin Member Posts: 1,071 ✭✭✭✭
    edited August 2020
    @IsoTherm

    well, this is a very interesting one

    First thing I would do is probably quit the program — sign out and then sign back in and see if that helps

    I’d also try drawing some arcs — first around one of those points at the bottom, and then around the other. I would do one at a time to see which one in particular might be the malfunctioning one

    The next thing I would do is just eliminate that bottom spline and redraw it

    If there’s anyway you could post a link to that sketch only, that would be interesting to look at





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    IsoThermIsoTherm Member Posts: 66 PRO
    I've done both of those things. I've recreated all of the splines, several times. I've placed points at locations along the two offset splines for the end splines to anchor to. When I highlight the constraints it shows that the end points of the splines coincide with the others, but when you pan in...they just won't close.

    Hate to be a noob - how do I share the sketch without sharing the rest of the document?

    grazzi
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    steve_shubinsteve_shubin Member Posts: 1,071 ✭✭✭✭
    @IsoTherm

    Copy sketch and then paste into a new document





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    bruce_williamsbruce_williams Member, Developers Posts: 842 EDU
    @IsoTherm
    you will need to make the document public for us to work with it.

    Here are instructions for posting -
    https://forum.onshape.com/discussion/9107/forum-post-checklist-read-this-first#latest
    www.accuratepattern.com
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    IsoThermIsoTherm Member Posts: 66 PRO
    sorry, thought I had. It's public now.
    thanks
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    bruce_williamsbruce_williams Member, Developers Posts: 842 EDU
    @IsoTherm
    I started playing with 'binary dividing lines' and found the lower right intersection is problem.  Once I trimmed the excess it enclosed.

    seems like one for support.  Although unconstrained splines are goofy...


    www.accuratepattern.com
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    bruce_williamsbruce_williams Member, Developers Posts: 842 EDU
    btw I am patternmaker and did a lot of impellers over the years.  nice to see this one!

    www.accuratepattern.com
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    IsoThermIsoTherm Member Posts: 66 PRO
    thanks for the help Bruce.
    Splines are strange beasts in every cad system I've ever used (many).
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    steve_shubinsteve_shubin Member Posts: 1,071 ✭✭✭✭
    @IsoTherm
    Although unconstrained splines are goofy...
    IsoTherm said:
    Splines are strange beasts in every cad system I've ever used (many).
    I wasn’t sure if you were going to allow us to copy the sketch. So I used the measurement tool to note the diameters and then I sketched over the image

    Below are your constrained splines. And man is it a busy sketch with all those numbers — unless you zoom in

    https://cad.onshape.com/documents/f48b0bce6bd61aa7b65332b7/w/df441d2f5248c3e85bb7a8e9/e/365d3d4236cb75e0f265634e


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    steve_shubinsteve_shubin Member Posts: 1,071 ✭✭✭✭
    @bruce_williams

    Nice work Bruce

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    steve_shubinsteve_shubin Member Posts: 1,071 ✭✭✭✭
    @IsoTherm
    @bruce_williams



    I’m always curious to see how the program works.

    So I wanted to look at the document IsoTherm posted of the sketch

    Wanted to see if I could sketch an arc around that lower right hand point (where Bruce showed was a problematic area), and have that banana shape enclose

    But when I opened up the sketch, I noticed that it was already modified.

    In the mean time, I notice the outside arc of the (impeller blade ?) had a line that I thought could be eliminated if things were made tangent

    So I went into the sketch that I made from scratch, and made the outermost spline tangent at the top and bottom in hopes of eliminating any unnecessary lines on the extruded part

    All of a sudden, I no longer have an enclosed shape.

    So I do the trick where you start drawing intermediary lines to see what part of the shape is not closed up

    By chance, I happen to start drawing a line on the inside of the inside spline, only I stopped before I crossed over that spline. I stopped right on the spline

    What happens? All of a sudden, the banana shape shows as being a closed shape. It’s gray between the splines

    1) OK so isotherm who has used a number of CAD programs is having a hard time getting this thing to work

    2) Bruce makes the statement that it looks like one for support

    3) I definitely got some peculiar behavior

    Hey tech — you guys should look at this

    Below is a link to the document I made from scratch, completely separate from IsoTherms document

    https://cad.onshape.com/documents/fb56b83d7a6a5ddc122ee8a7/w/efbbdc2318f612082e04ffd1/e/cd9a6d695955b8d2812e35b4


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    bruce_williamsbruce_williams Member, Developers Posts: 842 EDU

    that is behavior I saw on @IsoTherm document; nice way to replicate issue @steve_shubin
    www.accuratepattern.com
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