Fastening & Attaching

The Assignment:
In order to successfully construct our next project out of delrin,we needed to learn how to fasten and attach delrin to create both fixed and movable joints. A description of each method, as well as its advantages and disadvantages are below.

Piano Wire:

The piano wire method attaches two pieces by drilling a hole through the first 3 sections of the staggered pieces of the hinge, making sure that there is enough separation between them to allow the hinge to bend. Next we used a slightly smaller drill on the last prong so that the wire would be secured. We then used the press to push the wire into the last prong. This created a hinge that was both secure and easily bendable. The main advantage of this method is that it allows for the creation of movable parts. It is also useful because you don't need to measure the drilled portion out in solid works. A down side to this method is that if the hinge is much longer than the one pictured above, then the drill press won't be able to reach the entire way, to the last prong.

Heat Staking:

 

The heat stake, pictured above, is a very useful piece of equipment to use when attaching two pieces of delrin together. In this process, one first creates a two parts, one that has a hole or notch while the other has a peg that protrudes past the hole's surface. The machine head is heated to about 450 degrees Fahrenheit before it is pressed onto the peg. The pressure and heat fuses the two pieces together by melting them together to form a smooth bump in place of the peg and hole. The advantages of this method include it's permanence. Once fused the pieces are very well, and permanently attached. Also, the heat stake leaves a smooth bump rather than a sharp edge which would be useful in building children's toys or other things that shouldn't have sharp edges. The largest draw-back to heat staking is that once the delrin is fused, there is no way to get it apart without breaking it. This means that in order to repair anything underneath the heat staked pieces would be impossible without breaking those pieces. Another advantage of the heat stake is that the tolerances of the material and the exact fit of the peg and hole is not as essential as with the notch and peg method. I also tested the heat stake on a piece of delrin rod and a flat piece of delrin. Professor Banzaert and I weren't sure whether or not this would work since the rods actually have some glass in them and therefore would have a higher melting point than the delrin sheets. Despite these concerns, the method seemed to work well, and could be of use to my partner and I when constructing our windlass.

Notches & Pegs:
Like the heat staking method, this method involves two parts. One part that has a hole or notch, while the other has a peg. The peg, or edge of the part is then fitted tightly into the hole or notch of the other part. This method is useful because it offers a tight fit between two pieces without making them impossible to separate. This allows the pieces to be taken apart to allow for repairs or upgrades. One draw back of this method is that very small discrepancies in a part's dimensions could produce a part that either doesn't fit at all, or is too loose to be of any structural value. Given that the margin of error is already rather small, it doesn't help that there are often slight differences in the measurements of part made on solid works and the actual part that is cut. This is discussed more below.

Tolerances of Notches & Pegs:
In class we were given two sheets of delrin that had many holes for their respective pegs with slightly varying dimensions to show just how small the margin of error between a tight fit and one that was too loose or too small. We used the digital calipers to measure the dimensions of both parts. We found that the dimension that corresponds with the width of the delrin sheet was more important than the length of the opening.

1) Single Peg and Hole Measurements:
peg thickness: 3.13 mm
too tight:  <3.14 mm
perfect fit: 3.14 mm - 3.17 mm
too loose: > 3.2

2) Double Peg and Hole Measurements
peg thickness: 3.20 mm
too tight:  < 3.21 mm
perfect fit:  3.21 mm - 3.24 mm
too loose: > 3,24 mm

Discrepancies between Solid Works and the Actual Part:
Solid works.....vs.....actual measurements
.135 in.....(.145 in) (.1455 in) (.1435 in)
.125 in.....(.135 in) (.134 in) (.134 in)
.115 in.....(.1285 in) (.1185 in) (.119 in)

As you can see from the chart above, the actual measurement of the part can differ greatly from what is displayed in solid works. This could lead to frustration if not addressed in the testing stage of a design. Having done this exercise, I will make sure that from now on I test out the measurements on solid works versus the real thing to ensure that they fit together properly before cutting out a final piece.


Rods & Bushings:
      

The process of creating bushings for rods is almost identical to that of the notches and pegs method described above, except that it deals with a round opening and a rod with a predetermined diameter, Depending on the purpose of the bushings, the builder may want them to either be fitted or loose. A fitted bushing may be desired if the bushing is at the end of a rod and is meant to hold other moving pieces or the rod in place. A loose bushing may be desired if it is part of a larger moving part or is acting as a buffer between two parts. Bushings are extremely useful for securing rods and the parts connected to the rod, and like the notches and pegs they can be made tight enough to be of structural use without being impossible to dismantle.

We were also instructed on how to operate the band saw in order to cut our rods the appropriate length. This is useful because it is quickly at hand in the We-Lab and can be easily measured without worrying about whether or not it fits

Tolerances of Rods & Bushings:
As with the Notches and Pegs method, the bushings must have a diameter that falls in a rather small range. The difference between a fitted and loose bushing is so small that it is not discernible upon initial observation.

1)Measurements
diameter of the rod: 6.33 mm
tight fit: 6.46 mm
loose fit: 6.66 mm

Reflection:
Learning how to fasten and attach pieces of delrin was a very important first step in the process of designing our windlass. We can now informatively consider all the methods and choose the best one for that particular joint. I also learned that the dimensions that are set on Solid Works are not the same and thus it is very important to create test pieces before the final is cut.