Drawing a 2D spial.

[jonbikebod]

I am new to the forum and have never had a lot of success with CAD programmes. I never got anywhere with AutoCAD but have been more recently using SketchUp which has a much more gentle learning curve. My question is, how do you draw a 2D spiral? This is to form a scroll saw pattern. The idea being the table of the scroll saw is tilted a few degrees and when the spiral is cut out, the solid centre drops and the spiral forms sloping sides and locks to its neighbour. The rim is solid as well – I forgot to mention that.
I have found a number of ways of creating a 3D helix for ‘circular’ stair cases etc but not one for a 2D spiral.
Sorry, the above is a very inelegant explanation. What I think I am asking to draw is a 2D spiral between a small and a large circle that has a constant pitch between the initial and final gradient. Preferably in SketchUp.
Jon.

 

[tnimble]

There's probably a ruby script around for doing that.

Another method would be drawing a equally sided triangle. Make two copies of this triangle and butt them up. Then draw a larger equally sided triangle along the the longest compound side. Continue this process.

Draw a line along the triangle path to have a perfect spiral. Make the spiral line an group. Use this group in all your designs needing a spiral, use scale to fit it to a perticular size.

Like so:

Besides using a Padovan sequence, you can also use a Fibonacci sequence by using squares like so:

 

[jonbikebod]

That is extremely clever tnimble.
I love the organic shape the Fibonacci sequence gives. With these progressions, the distance between successive rotations increases, I need it to remain constant. Aesthetically more of a geometric spiral than an organic one. I would draw a sketch and post it but I have not posted enough yet.
Jon.

 

[Slim]

There is a helix script. There is a link in this thread (Dave R's second post)

I'm not sure if it can do what you want though. I did have a search for a spiral ruby script, but it kept turning up the helix one.

BTW, you only need three posts in order to post pictures.

 

[tnimble]

What you describe is not an spiral. In fact it cannot exist at all since there is no starting point possible. With every spiral the distance between revolutions becomes smaller when nearing the centre. When reaching the centre the distance between revolutions will be infinite small.

What comes nearest to your description is an Archimedes spiral which is draw very
similar.

(look closely to the centre to see the varying clearance)

Draw two lines perpendicular to each other of length 1 and connect the two ends (this will be a line of square root 2 long). From this largest triangle draw a line in its extend (sketchup shows this as a purple line while drawing) of length 1. Rotate this line to form a 90 degrees agnle to the root 2 line. And so on.

I could not really find a picture describing the construction so I made this one quickly:

 

[tnimble]

There is a helix script. There is a link in this thread (Dave R's second post)

I'm not sure if it can do what you want though. I did have a search for a spiral ruby script, but it kept turning up the helix one.

BTW, you only need three posts in order to post pictures.

A helix is a linear movement along a strait line constantly keeping the same distance from this line while rotating linear.

Like a spiral straicase, whos naming is uterly wrong.

 

[SketchUp Guru]

Here's a spiral of whatever sort it is drawn using the Helix script in SketchUp. Settings are 12" ending radius, 2" start. 0 pitch, 5 rotations, 24 segments per turn.

 

[Slim]

There is a helix script. There is a link in this thread (Dave R's second post)

I'm not sure if it can do what you want though. I did have a search for a spiral ruby script, but it kept turning up the helix one.

BTW, you only need three posts in order to post pictures.

A helix is a linear movement along a strait line constantly keeping the same distance from this line while rotating linear.

Like a spiral straicase, whos naming is uterly wrong.

Yes, thankyou tnimble, I do know what a helix is. :roll: I was suggesting that the helix script might be able to do what Jon wanted.

As it turns out, it can.

 

[tnimble]

Yes, thankyou tnimble, I do know what a helix is. :roll: I was suggesting that the helix script might be able to do what Jon wanted.

As it turns out, it can.

Sorry if I've offended you in any way, wasn't meant that way. I've downloaded that helix script linked by dave r in his second post and it draws a nice helix.

Not that spiral alike shape of the post in this thread by Dave R. The settings he here mentions aren't in the dialog box of the helix script. And if those options would be there the script would be hopelessly misnamed.

 

[SketchUp Guru]

Who cares what the name of the script is? Most people don't know or care. You're being pendantic. :roll:

The script has been updated and does include the option to make the settings.

http://www.crai.archi.fr/RubyLibraryDep ... helix13.rb

 

[Slim]

Sorry Dave, I didn't realise the helix script had been updated. I gave the link for the old one.

 

[SketchUp Guru]

That's OK, Simon. I'd forgotten about that thread and it hadn't come up before now.

 

[tnimble]

Who cares what the frickin name of the script is? Most people don't know or care. You're being pendantic. :roll:

If that's being pedantic let us next time call them parallel vices. Its just confusing. A better name for the script would be spring13.rb

Thanks for the link tho, much appreciated.

 

[jonbikebod]

Thanks Dave R that gives me exactly what I was after. Thanks Tnimble and Slim for your input, I fear I caused confusion with my terminology but then it seems the terminology frequently gets misused.
Cheers,
Jon.