Fastening & Attaching

The other day in class, I learned different methods of attaching pieces of delrin to other pieces of delrin. My partner, Tiffany, and I rotated through different stations were we learned how to heat stake two pieces together, use piano wire to connect pieces, and use notches/pegs to connect delrin.

Heat Staking
Heat staking is a process where one leg of a t-shaped piece of delrin is fit into a hole in another piece of delrin. The delrin is then melted together. This method is beneficial if the pieces need to be permanently attached to each other. The only way the pieces could come apart after they are connected in this way is to break the piece. This is useful for making objects that need to stay together, like toys for children.

Piano Wire
This process is good for putting two pieces of delrin together in a hinge. It allows for movement of the two pieces. It is good if the point is for the pieces to be able to move together. The drawbacks of this process is that it is not useful if the pieces need to stay together at a rigid angle. It is not as permanent or stable as the heat staking process.

Notches/Pegs
The benefit of this process is that it allows two pieces to stay together pretty tightly, but it is still possible for the pieces to come apart if needed. This would work well if there was something inside that would need to be taken out to be fixed or upgraded at a later time, while still retaining a tight bond. This process is not as permanent as heat staking, but if the tolerances are right, it could be very hard to take the pieces apart. The drawback to this method is that it can take a couple tries to get the sizing right on the notches and pegs. If the sizing is too loose, the two pieces won't hold together.

Tolerances

A Width of Sheet of Delrin: 3.15mm
Width of Notch:................... 3.16mm-Tight Fit
                          ....................3.33mm-Loose Fit
B Width of Sheet of Delrin: 3.33mm
Width of Notch:....................3.34mm-Tight Fit
                          ....................3.52mm-Loose Fit

For the A, the dimensions specified in solidworks for the width of the notch were
Tight Fit: 3.175mm (.125 inches)
Loose Fit: 3.429mm (.135 inches)

The tolerances differ in solidworks as compared to what really came out because the laser cutter is not exact. It will cut a piece a couple times before it cuts all the way through the material. The tolerances will also differ for different material thickness because it takes more power and possible more passthroughs to fully cut the piece. This means that it is necessary to test the measurements of the notches and pegs on the laser cutter in a smaller piece before building the entire part. The measurements may not be correct the first time the piece gets cut out.

Bushings

Tight Bushings are necessary for keeping a piece in a specific place on a rod while loose bushings are necessary for enforcing the strength of a rod.

Measurements-diameters

Rod....................6.35mm
Loose Bushings:6.52mm
Tight Bushings: 6.37mm