Sliding bolt - can't figure out tangent mate

gary_nielsen

I figured out how to get a pin to move in a slot using a planar mate and a tangent mate. What I can't figure out, is how to do it on a curved surface. Here's where I am:

I can get the green pin to follow the curve on the right. On the left, I cannot figure out how to get the green pin (attached to the green cylinder) to follow the slot. Here's the link to my OnShape document.

TimRice

Gary, try creating a sketch down the center of the curved slot. You will also need a sketch with a sketch point located at the center axis of the cylinder. Insert these into the assembly and use the group to constrain the sketches to their respective parts. Then you can use the tangent mate between the sketch point and the other sketch curve.



https://cad.onshape.com/documents/e3540e78b124d8da80df830f/w/2104fa5fa5f7ac225cfdcaaf/e/df292a380ae666f03dcd642c

TimRice

Gary, try creating a sketch down the center of the curved slot. You will also need a sketch with a sketch point located at the center axis of the cylinder. Insert these into the assembly and use the group to constrain the sketches to their respective parts. Then you can use the tangent mate between the sketch point and the other sketch curve.



https://cad.onshape.com/documents/e3540e78b124d8da80df830f/w/2104fa5fa5f7ac225cfdcaaf/e/df292a380ae666f03dcd642c

philip_thomas

Tims answer is spot on - that said, i am going to offer some additional insight that may help others

• Tangent mate is intended for cam-follower type scenarios. These are characterized by the follower touching only ONE face of the cam at any given point. In this example, if the pin is the same width as the slot, then it is simultaneously touching two of the faces and will likely act in an unpredictable fashion. 
• At the end of each slot is a singularity, meaning that the solution cannot move forward and does not know that the only viable path is backwards. In this situation, the follower often gets stuck.
• Tangent mate is an expensive mate (lots of CPU to solve), the sketch solution solves much faster.

Have fun!

craig_puetz

The above solution is exactly what I am looking for, but I am missing something. I created the trajectory curve - a radius and two straight sections. I insert it into my assembly, but can only follow one segment, not all three. What am I missing? I have explored group, but without any success.

philip_thomas

Craig - hello.





Our bad, not obvious how to do it. This is a special case where you have straight line segments - this makes it a little harder because tools like '3D fit spline' (thank you Bill Campbell) do not work well. 
The steps are:

• Extrude the sketch to create edges
• Use 'Unified Spline' to convert the edges to a single curve
• Convert the curve into a sketch
• Insert the sketch into the assembly

Someone may be able to improve this, but this should get you going.
Good Luck!

https://cad.onshape.com/documents/26374636f556d7f2f2abee3a/w/68dc3d9b9f67abee5b565ae5/e/65acb15543adfe03e12063d5