Closed spline with one corner

[mrbump]

Hello everyone, new guy here.

 

I'm having problems sketching a closed spline with a corner. Think of a drop shape for instance or an airfoil cross section (which is what I'm actually trying to do).

 

As soon as you close a spline, the first/last point gets rounded as well. And I can't find a way to get the spline handles of a point to act independently.

 

I can do this:

1. Draw the shape in two separate halves (splines)

2. Connect the bottom end of the drop, where it should be rounded

3. Make the two splines tangent

4. Connect the upper pointy end of the drop

--> spline handle of the upper point now behave independently from each other.

 

There are some problems with this though:

The spline handles at the bottom of the drop are now fixed

The tangency icon actually moves next to the joint which is not tangent at all - this makes me think I'm doing something that should not be done.

 

Does anybody have a suggestion how this can best be done? Thank you in advance.

 

(Sorry if there is an obvious solution to this. I'm a bit of a SW newbie - and google was a bit unhelpful on this issue)

 

mrbump

[welldriller]

mrbump:

 

I will be back --- Not sure what shape you are trying to make but did a drop ok but forgot to try to stretch it. Will try that and get back to you

 

I am back -- I did the following autocadlt 2000

 

make a 12" horizontal line

make a 1" vertical line

make a 2" vertical line

make a 4" vertical line

 

NOTE: after you offset the vertical lines erase them from the end of the horizontal line.

 

I started on the right side of the horizontal line and off set to the left.

 

set snap on so that you can find the center and end points.

 

move the 1" vertical line to the end of the horizontal line

offset it 1"

move the 2" vertical line to the end of the horizontal line

offset it 2"

move the 4" vertical line to the end of the horizontal line

offset it 6"

 

choose spline

start at the left end of the horizontal line and go to each end of the vertical lines (and the other end of the horizontal line) and end up back where you started.

 

erase the horizontal line and the vertical lines

 

You can then use the line command to make the rest of the air foil

 

Hope that this has been some help

welldriller

Edited January 20, 2013 by welldriller
Had to check if this would work.

[mrbump]

Thank you very much for your efforts welldriller. Unfortunately we seem to have a bit of a compatibility issue as I just can't get my solidworks to draw autocad splines...

 

Anyway, it made me realize that my question seems to be a bit unclear.

 

So, what I want to do (using SolidWorks 2011) is draw cross sections of an old airplane propeller and then create a surface. These cross sections are closed curvy lines with the exception of the trailing edge which is a corner or pointy.

For those people that have no idea what I'm rambling on about I introduced the substitution with a drop shape.

 

I made a few screenshots to illustrate the process:

1a: This is what I want to get to, but it's not closed yet (I'm in the middle of drawing it, but the mouse pointer didn't make it onto the screenshot).

 

1b: It's closed now but it magically turned into an egg. The intuitive thing would be to declare the upper point a "corner" - but I can't find a way to do it.

 

2a: I was toying around with some workaround ideas how to get there. Dividing up the single closed spline into two splines, then moving and connecting the dots.

 

2b: Making the two splines tangent actually only makes one end tangent and puts the tangency relationship icon next to the end that isn't tangent. But the real problem is that the direction of the spline handles is now locked. I would like the handles to behave naturally - ideally they wouldn't even need manual tampering.

[welldriller]

mrbump:

 

Sorry, I am not familiar with SOLID-WORKS, but will look into what I can do to help find a way to do this.

 

I am new to the forum and do not know how to download pictures to show you what I do in AUTOCADLT 2000.

Will also work that.

 

If you would like to use email I may be able to send you a copy of my drawings.

 

Thank you for your information

welldriller

Edited January 21, 2013 by welldriller
remove email address

[mrbump]

Thanks again for your efforts welldriller. But please don't regard it as your personal mission to help me - especially as you're not familiar with the program. I don't want to take up too much of your valuable time.

 

 

May I also suggest that you edit your post to remove your email-address as soon as possible. It's in your own interest.

 

Best regards,

mrbump

[welldriller]

mrbump:

 

I took your advise and removed my email address. I would like to apologize but you are correct your program and knowledge is far superior to mine, but I have a bad habit of trying to help if someone has a problem regardless of what it is.

 

Thank you for your Patience

welldriller

[JD Mather]

Is there any portion (no matter how small) at that connection point that can be linear rather than a spline? (on one side or both?)

 

[welldriller]

Mr Mather:

I am butting in again, but does your program have a ARC command that would work for you?

 

welldriller

[JD Mather]

... but does your program have a ARC command that would work for you?

 

Yes, the Arc command works for me.

All of the commands work for me.

[mrbump]

Thank you for your suggestion. This will probably be a reasonable work-around given the not so preciseness of the project. I'll give it a try and report back. Alternatively I might just give the pointy end a certain thickness using a straight line or an arc. (I wanted to create the loft razor sharp and fillet it afterwards, but I guess it can also be done beforehand).

 

Just for my general understanding:

Is it correct then, that there can be no corner in a single spline (where the two handles move independently)?

Additionally there is no way to have a tangency relationship between two splines that allows the spline handles at the joint to behave in a natural way (as with points within a spline)?

 

Thanks again

mrbump

[Dadgad]

Yes, the Arc command works for me.

All of the commands work for me.

 

They must really like you!

[JD Mather]

(I wanted to create the loft razor sharp...

 

That is the geometric description of two lines. Why can't you simply use a line at the beginning and end of the spline? Sounds pretty obvious to me?

[mrbump]

Well, it is the description of two lines that can also be curves.

And I'm sometimes a pedantic purist...

 

Anyway, as I said, if the workaround is the only way to go I'll gladly live with it. I just wanted to make sure I didn't miss the simple "real solution".

 

Thank you for your help.