Trimming the outside of a circle from various points

I've attached a screenshot. Ultimately what i want to do is create a planar surface that i can extrude.

My problem is that for the past four hours of trial and error, and forum/google searching i couldnt figure out how to do it. I want to make a gear that looks similar to the rhino curves. I want to do this by trimming the two outer circles against the points shown in the image. Its important that i trim the circles because i want to retain the radius.

Another note, i think that the 'sprocket' shapes are misleading, i tried to draw diagonal lines from end pt to start pt within each sprocket, but they get all crazy as if everything isnt aligned. I do have some rotate components in there but i'm not sure that they are extreme enough to where i'd be getting the results that i'm getting.

Its very discouraging when i want to figure things out myself but cant do it after literally 4-5 hours.

Thank you all for your help, i greatly appreciate it.

Attachments:

Problem_001.jpg, 615 KB
definition.gh, 17 KB

Replies to This Discussion

Permalink Reply by greg antons on June 29, 2013 at 1:01am

NEVERMIND... i got it after many hours of frustration. I'll upload in case anyone wonders how to do it. its a mess but here it is...

Attachments:

definition.gh, 16 KB

Permalink Reply by David Rutten on June 29, 2013 at 6:34am

I came up with another approach. My idea was the to create a dash/gap pattern on the outer circle, then scale all gaps outwards to create the teeth arcs and leave the dashes in place to be the other arcs. Add some [Extend Curve] logic to make the arcs shorter to achieve the slanted edges and then stitch it all together into a single curve.

I did find a bug in the Dash Pattern component which often results in a failed result, so I also attached the updated Curve.gha

It's a fairly finicky solution as a lot of slider value combinations result in an impossible sprocket, but at least it's fast as it doesn't require any region booleans.

David Rutten

david@mcneel.com

Tirol, Austria

Attachments:

sprockets.gh, 15 KB
Curve.gha, 611 KB

Permalink Reply by Igor on June 29, 2013 at 5:41am

If you project real gear it will not work. The form of teeths of a gear should have the evolvent form. Here is cluster http://www.grasshopper3d.com/forum/topics/evolvent-gears which does gears, but in it there are small discrepancies because of which these gears will get jammed. I once altered it, if I find on the computer I will send to you.

Permalink Reply by greg antons on June 29, 2013 at 11:45am

thanks to both of you. Igor, I think the solution you provided is a little more technical and accurate. I am going for simple geometric shapes that i could adjust parameters without having to rebuild them in rhino. But thanks for sharing your link, its very interesting stuff.

David, i downloaded your definition and saw that the gap was kinda buggy. but when the gear wasn't working right, it was still pretty predictable (if the gap is too small the definition fails, etc). And yeah its a little bit faster than what i have too. I think i'll stick with mine, because it took me many many hours to figure it out... but i will use yours as a reference to help me get better with grasshopper.

thanks to both of you for your replies :D

Permalink Reply by roderick read on November 27, 2013 at 3:35pm