Fastening & Attaching

On Tuesday, we spent the class visiting stations set up around the classroom in order to learn about the tools for our next project. My partner, Rachel, and I decided to start with the Drill Press, Arbor press, and piano wire station first.

At this station, we learned how to use piano wire to fasten two pieces, that fit like puzzle pieces, together. The Drill Press puts hole/s in the piece and then we use an arbor press to push the piano wire into the piece. This combination is what fastens the two pieces together. This method of jointing allows 270 degrees of rotation. However, it is difficult to line up the pieces so that the joined pieces allow for that full degree of motion. If not enough of a gap is left between the pieces, the edge of the pieces will hit one another, preventing the range of motion that is a benefit of this method of attachment. As a result, this form of attachment requires a lot of trial and error. The Drill Press/Arbor Press is very useful for creating a connected piece that is able to rotate.

The next station we went to was the heat staking station. This machine was pretty easy to operate. Once the pieces were aligned underneath the nozzle, the machine was heated up to it's desired temperature, 450 degrees, it is then lowered and held on the piece. When the piece is sufficiently melted, and as a result attached, the machine is turned off and a stream of gas is blown onto the nozzle and piece to cool it down. The attachment created by the thermal press is permanent, which could be both a benefit or a drawback depending on what you need it for. The use of the thermal press is best for creating a permanent connecter between two pieces.

The last station we went to was the slots/peg station. At this station we took the measurements of rods, bushings, and pegs to get a better understanding of the degree of accuracy of the laser cutter. We also had a chance to see how slots and pegs could be used to join together two pieces. The slot and peg method, is probably the easiest of the above methods because once the pieces are printed, to assemble, you just snap the two pieces together. If the measurements were done correctly, correctly factoring in the accuracy of the laser cutter, the pieces should fit snuggly together. This method does allow for the pieces to be attached and detached repeatedly. After too many repetitions, however, the fit becomes looser, so the slot peg method isn’t great for projects that require connected joint that opens and closes repeatedly.

As I mentioned earlier, at the slot/peg station we also took the measurements of various bushings and pegs. The bushings came in three different fits that were all relative to the rod it was been fitted around. All measurements were made with the use of a caliper, a device that measures the distance between two opposite sides of an object. In the data below I took 3 trials for each measurement. The data from these recording is where the +/- # value comes from – the variation in the data.

The found that the rod had a diameter of 0.250 in. +/- 0.001. In comparison, the loose fit bushing was roughly .0015 +/- 0.001 in. larger in diameter. The snug fit was roughly 0.0025 in. +/- 0.001 in. larger in diameter and the pressed fit was approximately .0009 in. +/- 0.001 larger in diameter.

The tighter bushings, because they don’t move around easily across the rod, would be really good at acting as barriers that prevent other objects on the rod to slide all across the rod as well. These tight bushings are really similar to shaft collars which have a similar function.

The looser bushings seem to work similarly to spacers – creating distance between two objects that shouldn’t rub against one another (e.g. metal against metal).

The peg had a thickness of 0.1260 in. +/- 0.0005. The loose fit had a height 0.145 in. +/- 0.002. The snug fit had a height of 0.1350 in. +/- 0.0010. The pressed fit had a height of 0.1195 +/1 0.004. It is also important to note that for the peg/slot measurements we were able to compare the recorded data with the height that was specified in solid works. I found that across the board, the data that I measured had a discrepancy of approx. 0.01 in. for both the loose and tight fit slots/pegs. This discrepancy seems to be a result of the laser burning away more than specified because the heat of the laser melted away parts of the delrin that wasn’t meant to be melted away, during the creation of the part. It could also be a result of use throughout the day. The pieces were repeatedly and forceful being shoved into one another, which could also explain the discrepancy between the intended value and the actual value.

This is definitely something important to keep in mind when working on our Windlass assignment. It is better to make the slots slightly smaller than intended, subtracting the 0.01 in. discrepancy that I saw in my measurements (or make the pegs slightly bigger), to ensure that the peg/slot pieces will continue to do their job and hold each other in place. In general practice, this discrepancy created by the laser cuter should be remembered especially when dealing with pieces that require very precise measurements.