Logarithmic Spiral

[jmwidell]

Hello All,

I need to model a logarithmic spiral (like a clock spring) for an application. If I generate this manually, it's going to take approximately 150 arcs. (graduating outwards, 10 degree arcs, and as spiral centers graduate to one direction) I have an example, but can not attach. Figures, huh...when you really ned the help. Has anyone modeled one of these, or know where I can download one. This way I can see what the workflow is.
I did a seearch here for this, but only regular spirals cam up.

Thanks in advance,
Jack

[JDMather]

What is your manufacturing tolerance? You could probably get by with far fewer rays.

[jmwidell]

Thanks for your response, JD. First, I broke a rule, and didn't specify that I am using IV2002 SP3. Theerefore, I was unable to open your file. As far as manufacturing tolerances go, this will end up being a purchace per print application. (some dimensions can be fudged) The model does not have to be "perfect", but at least meet material thickness, ID, width, center opening diameter, and the distance from the center to the center of a loop that is required at a point 3/4" from center. That was a mouthfull. Does "enough to get by with" qualify as a professional response? 🙂 Yes, fewer rays may be the answer to saving a bit of time.

[JDMather]

http://mathworld.wolfram.com/LogarithmicSpiral.html I used the geometric method part way down the page. Used Construction lines for the perpendicular lines and rays and then sketched overtop with Spline. I think I used 30 rays but you might try with 15.

[Anonymous]

Did you try selecting Spiral as the Coil type? If
you type spiral in the help index, you should get a link to the coil topic.

Loren Jahraus

Autodesk Inventor Product
Design

[jmwidell]

Ahhh...intersting. Thank you for the link and taking the time to help. I shall begin addressing this in the morning. Heck, now I may not get any sleep. Maybe I'll play with it at home. I'm sure it will hit me in the shower! 🙂

Regards..........Jack

[JDMather]

As Loren pointed out there is a Spiral command built into the Coil command. You initially indicated you had done a search so I assumed you are aware of that. I'm not sure what formula the Inventor spiral uses.

[jmwidell]

Thanks much Loren and JD. JD, I am still playing around with the spiral as a Logarithmic, but I achieved good results with the spiral tool under Coil. I had to play with this just a bit to get the correct diameter and end stop position, but it worked very well for my application. Thanks again for your interest and helping me.

Regards,

Jack

[Anonymous]

I am pretty sure the Coil spiral maintains an
equal spacing. You have to enter a pitch, so the distance between coils at any
point on the spring should be equal to the pitch. I haven't actually
measured it, so if someone finds it doesn't do that I will get the algorithm
from development.

Loren Jahraus

Autodesk Inventor Product
Design

[Anonymous]

> pitch


r = a * theta or Archemede's spiral.

[devin.herritz]

How exactly did you make that spiral? I am trying to make a Logarithmic spiral involute curve and I cannot figure out how to do it. I'm not exactly sure what tool to use, and there aren't any videos on the internet. 

[graemev]

Would it be better to use a loft instead of a sweep or extrude?  I'm imagine making a few cross-sectional sketches, perhaps at quadrant points around the perimeter, should be within "fudge-able" margins for the desired effect.

[JDMather]

This is a very old thread. The soluton has changed.

Inventor now has an Equation Curve funcion.

Pretty sure there are some youtube examples.

What is the formula for your desired curve?

[JDMather]

---

@graemev wrote:

Would it be better to use a loft instead of a sweep or extrude?  I'm imagine making a few cross-sectional sketches, perhaps at quadrant points around the perimeter, should be within "fudge-able" margins for the desired effect.

---

Can you post an example ipt file that demonstrates this technique?

[devin.herritz]

To tell you the truth I'm not really sure. I just know that It needs to look like this.

http://mathworld.wolfram.com/LogarithmicSpiralInvolute.html

[graemev]

It's ugly rough for an example, but you get the drift.  Size, math, and quantity of sketches involved to your taste.

[devin.herritz]

The thing is, I have to make it a line, not a profile. Like, in sketch mode.

[JDMather]

Have you tried using Equation Curves yet?