Circular pattern with user parameter controlling angle of notch

[eric941]

Hi,

I am setting up a family of parts that consist of a round disc with a fixed OD and a circular pattern of notches cut into the OD. The notches must go to a certain depth from the center, so those parameters are set. My problem is that I need to control the amount of material left between the notches, along the OD, after the pattern is done. Given the fixed parameters of the major OD, minor OD (3.5" in this case) and number of notches, the only way to control the amount of material between notches is to change the angle. When I set up the sketch to do the notches, I can only get a fully constrained sketch if I assign a specific angle  to the notch. I need to be able to set it up so that the angle of the notch varies so the end result is a specifc amount of material left after the circular patter is sompleted.

In the attached PDF, I show what I have done so far. In this case the OD of the part is 4" and the diameter of the notch at it's closest to the center is 3.5". So basically, I end up with a driven parameter of 0.443. If I assign this value the parameter of d14, I need to make it equal to a ratio of another parameter (let's call it d15) so that d14 = d15*2.. This can only be acomplished by changing the angle.

In my family, the major OD and minor OD remain the same, but the angle must change to retain a specific amount of material between the notches when the number of notches is increased or decreased.

Is there an iLogic rule I can write to control this?

[eric941]

Sorry, forgot to add PDF of screen.

Eric

[JDMather]

still no pdf?

an ipt file would be better.

[eric941]

Let's try this. Don't know why it wouldn't let me upload the PDF.

[eric941]

Hi JD,

I think I have it figured out and will post solution as soon as possible. I didn't want you to spend any more time trying to solve my problem as I think I have the solution.

Eric

[eric941 · Accepted solution]

Hi JD (and anyone else looking at this),

I realized that my problem was not defined correctly and the initial ipt would not allow me to do what I needed to.

Simply put, I needed to control the chord length of a section of a given diameter circle.

The new ipt and linked spreadsheet establishes the method I am using to contol the parameters I need to control for the desired outcome.

The formula for chord length is (0.017455)(R)(A) where R is the radius of the circle and A is the angle of the chord (measured from the center point).

If I want a 0.150 length chord on a 4" diameter circle, the angle required would equal 0.150/(0.017455 * 2) = 4.2968

The total spacing (in degrees) for a notch and it's backing would equal 360 divided by the number of notches. So 12 notches would equate to a 30° spacing for one notch and the remaining material on the OD.

If I then subtract the 4.2968° result (from above) from the total angle per notch of 30° I will get the required notch angle (25.7032°)

Once I set up the model with construction lines from the center point to the OD, renamed the parameters and set up the spreadsheet with the proper formulas, wrote a rule for controling the parameters I needed to and establishing custom iProperties, everything worked.

If anyone has a simpler way, please let me know.

Eric

I have tried repeatedly to post attachements of the ipt and related spreadsheet with no luck. I click "Browse", clcik on the file and then Add Attachment and no attachment shows on the post. Any thoughts on that...I thought I knew how to do it.

[eric941]

Seems I can't upload files from my work computer. I'll have to talk to the IT guy about that.

Here are the IPT and Excel files I set up to test my solution.

Eric