Marble Roller Coaster – Designing Connectors (Part 2 of many) [VIDEO]

Article by Adam Bridgman, CSWE updated July 15, 2013


To read the first part of this series of articles, please CLICK HERE.

The next step is to design the connectors.


The marble is represented by a circle, a typical marble is 5/8” diameter so that is what I am designing for. There is a limitation to my design that reducing the diameter of the marble will have a significant impact on mass and therefore momentum, use a larger marble may be considered later based on simulations.  Therefore the design should be flexible to accommodate this.

This is just the beginning of the sketch, the design will need to be modified into being a connector, not just rails.


The key characteristics of this sketch are:

  1. The dimensions are related to the outside of the diameter, not the center, this means that if the diameter of the marble changes the spacing of the rails and the size of the connector will also increase.
  2. There is a clearance around the marble also based on the size (created using the offset sketch tool) so the marble will never bump the connector
  3. The size of the rails can be increased or decreased if simulation shows that they use too much material or are not strong enough.

This connector will eventually be split into both the male and female portion.  Therefore it must be thick enough for this purpose.  I used an initial value of 0.125in, but this can be adjusted if necessary.


To split the part into two separate bodies I sketched a jagged line, splitting the part into 2/3 on half and 1/3 on the other half.  Then I used a surface extrude both directions through all.


This surface can be used with the split tool to create 2 separate bodies in this part.


Each of these bodies should have dowels to ensure that the rails line up.  To do this I will share a sketch and apply a slight draft to the boss, but not the cut.


Hiding the other body ensures that this boss is only applied to this body.  This sketch will be shared between the two bodies so they will always have mating sizes.



Cut the hole that fits tightly with the bolt, so that the bolt part can be added (insert, part) and has something to be mated to.


To make sure there is a small clearance between the bolt and the threads I will used a scale feature.  But to use the scale and scale it about a specific point a coordinate system is necessary, to position the coordinate system in the middle of a hole a sketch a point is necessary (reference geometry, point).


Then a coordinate system can be made  (reference geometry, coordinate system)


Scale the bolt  about the coordinate system (leaving the scale in the z direction alone so the pitch is not changed).


Finally use a combine feature to subtract the threads from male connector.


If we want to separate these two bodies into separate part files we can use save bodies to do this, but since we will always want to use both, we can just use move/copy bodies to separate them.


Note: the value of 3in will be changed as required.

The finished part will look like this:


As always, I created a video in support of this article:

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Adam Bridgman, CSWE

Adam Bridgman in SOLIDWORKS Certified Expert proving customers with technical support and training