Fastening and Attaching

Delrin, or Polyoxymethylene is a stiff thermoplastic that has high stiffness and low friction. These properties make it suitable for precision parts such as ski bindings and small gear wheels. Because of Delrin's low friction and water absorbance, glue doesn't work when binding pieces together. In class, we practiced three different ways of joining the Delfrin. First, by heat staking, where the Delfrin is melted together in an immobile joint. Heat staking is useful when you know exactly where you want the joint. Once a joint is heated, it becomes completely joined and unable to be taken apart. This is the strongest attachment. Piano wire joints are movable joints where a piece of wire holds together two pieces of Delrin. This is one of the weaker joints because the wire can come out fairly easily but it preferable when you need a hinge-like joint. Notches and pegs are a bit of a happy medium between the two joints. It is an immobile joint where one piece of Delrin fits snugly into another piece. It is possible to get the pieces apart but when measured tightly can be a fairly permanent joint. 

Tight bushings are useful when you need to keep a piece in place, specifically a rod. Loose bushings are useful when the rod needs to be mobile, such as the rod that pulls of the string attached to the water. For the bushings, the difference between a loose and tight fit was about 0.01 inches. 

The discrepancies between the dimensions were about 0.01 inches for the 0.135 inch notch. For the the 0.125 inch was about 0.012 inches larger. The tightest notch, the 0.115 inch notch was from 0.005 to 0.01 inches. The tolerances are the same for different thickness materials. In the future of laser cutting, a thinner laser would make the tolerance more accurate to the model.