# Thread: Spline tangent problem - Spline on path of circles

1. ## Spline tangent problem - Spline on path of circles

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Hi all, I am new here

I am drawing a CAM that was designed, the CAM has a follower and after it it's attached to another turning piece, so you could say the whole thing is one big Bearing, you could call it a CAM Bearing. Anyway

I've drawn a set of circles along the path of the CAM (the circles are the follower), now I need to make a spline that fits that path. The problem is, that spline always intersects my circles. I need it to always stay tangent to the circles (ie. not intersect)
I have tried many ways and one way was to make the spline connect at the mid points of the circle but it still doesn't work.

I have attached some photos and also the DWG

Thanks people

2. No idea how you'd get it done in AutoCad, although it brings back memories of constructing equations of splines using numerical methods.

3. I just need to draw a curve that's tangent to those circles, the curve must not intersect.

I'm open to ideas and if I may need other software that you know of please say.

Otherwise I'm sure this can be done in AutoCAD, even if you have to make a script for it

4. Splines are tricky and do not always pass exactly through the points that you want.

Have you tried to join the points with a polyline using short straights between points, and then using the Fit option. When you do that, the polyline nodes stay at the picked points, and do not wander

5. The image appears to show a spline created with the CV method as oppose to the FIT method. That is only speculation, however, as I couldnâ€™t find the spline in the drawing.

Here is a spline created via Fit Points; it seams pretty good.

Edit: I'm late. It is all just redundant information now.

6. Hi system
I think your method of constructing spline is not correct. One possible way is to draw a spline passing through the centers of circles and then offset it with the radius of the"followers" (7 in your sample).

7. Use the CAM Generator Design Accelerator in Autodesk Inventor.

If you really want to do it in AutoCAD - become familiar with Parametric Constraints and be prepared to do a lot of work depending on how accurate you need the curve. (In Inventor you can simply enter then number of points on the curve that you want Inventor to calculate - all dialoge box driven - the software draws the cam.)

See pg 7
http://home.pct.edu/~jmather/AU2007/...2%20Mather.pdf

8. First, Thank you all for helping

eldon : I have tried your method and it seems to be good. except for the first circle.

SEANT : I have drawn it with a Fit Spline, the CV spline is very bad for this. Fit Spline seems good but when you zoom in you can see that it still intersects

Stefan BMR : Will try your method as soon as I can.

JD Mather : Thank you for your offers, I have Inventor and this drawing is actually for that, I have tried the Cam Generator and it only seems to draw the Cam but not the cut or groove the follower makes, (as the 2 parts will both be spinning, this cam does not convert rotor motion to linear motion, it is rotor to rotor, 3:1 reduction I think) It is not much of a Cam actually, it's a circle off centre. Also, AutoCAD parametric constraints can't seem to apply to a spline

I have attached what the final part should look like (the curve looks good but its not), as inventor does not accept the spline curve, I have contact solver turned on and I cannot fit the part into the other one. Because the followers are touching the curve (hence the intersecting spline in AutoCAD)

I am not sure how accurate Inventor wants that curve to be able to fit it.... I am now trying all your methods to see if Inventor will accept it, but Inventor has shown to be pretty picky especially with stuff like Tangent Constraint

9. Originally Posted by the_system
eldon : I have tried your method and it seems to be good. except for the first circle.
You can set the Tangential direction at any node, and would probably improve the line if you did set it for the first point.

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Ok I have solved this using the Cam Generator in Inventor ! It was under the extra settings "outside path"

But the other methods in AutoCAD i think worked as well

Thanks

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