Fastening & Attaching

This past Tuesday, we learned different ways of how to connect Delrin as well as how there are different fits of bushings on a Delrin rod and of slots and pegs. The classroom was divided into three different stations: the thermal press/ heat stake, the drill press, arbor press, and piano wire, and Calipers.

At the thermal press/ heat stake station, we learned how to melt two pieces of Delrin together to create one piece. This would be a very good technique for permanently connecting two pieces together and creating a stable part. It would be great at making the base of something that we would not want to move very much. It would not be very good for creating a movable and flexible part. It also causes one piece of Delrin to have round nub on it.

At the drill press, arbor press, and piano wire station, we learned how to connect two pieces of Delrin together by drilling holes in them and connecting them with piano wire. The benefits of this technique are that it is not permanent and so the pieces could be disassembled, it seems to be sturdy, and the pieces are movable and flexible yet still stay connected. Another great thing about this technique is that we can choose how tight or loose we want the holes to be and so we can decided if we want the delrin piece to be able to move all the way around the piano wire or if we want it to be held tight and steady by it. This technique would be great if we were making a bridge. The drawbacks of this technique is that there would be permanent holes in the Delrin and so placements of the holes must be well thought out and done correctly and it is also not permanent.

At the calipers station, we learned about how to connect pieces by designing them to be pegs and slots. We would design one piece to have the peg part that juts out on one of the sides while the other piece has the slot where the peg would go into. This technique would be good for creating designs that we would want to be able to easily disassemble like a fold-able table. This is also great because we can choose how tight or loose we want the pegs and slots to be. A tighter fit between the pegs and slots would create a sturdy design. A few drawbacks of this technique are that two parts would not be very movable and flexible and it is not permanent.

At the calipers station we also learned how to use calipers in order to measure bushings, rods, and sheets of Delrin.

Here are the measurements of the different types of bushings as well as the rod. There seemed to be at least a 0.02 mm difference between bushings of the same fit. The rods' measurements seemed to be the same though.

Bushing Fit Type	1st measurement	2nd measurement
Loose	6.58 mm	6.60 mm
Snug	6.37 mm	6.39 mm
Press/ tight	6.22 mm	6.28 mm
Delrin Rod Measurements	6.35 mm	6.35 mm

A press/tight fit bushing had an inner diameter much smaller than the rod's diameter. The press fit bushings' diameters fell in between 6.22 mm and 6.28 mm which seems to be a fairly large range but they are still smaller than the actual diameter of the rod which explains why it is difficult to place a press fit bushing around a rod. Tight bushings are most likely used to connect pieces that you would not want to move a lot or barely at all. It would be used to keep a section steady.

Meanwhile, a loose fit bushing has a much larger inner diameter than the rod. There was around a 0.25 mm difference between the diameter of the rod and the bushing explaining how easy it was to place the loose bushing around the rod and move it about. A loose bushing would most likely be used to connect pieces that one would want to still be able to move and bend.

Next we measured the slots made from Delrin.

	Actual measurement	SolidWorks measurement	Discrepancy between measurements
Line 1	0.141 in	0.135 in	0.06 in
Line 2	0.133 in	0.125 in	0.08 in
Line 3	0.125 in	0.115 in	0.10 in

The actual measurements were larger than the SolidWorks measurements. This could be due to the laser cutter cutting through the Delrin unevenly. We learned that the upper portion of the plastic would be melted down more than the lower part since the laser goes through top part more than it does the lower parts especially if the plastic must be cut more than once. Since we had the caliper tips touch the bottom of the slot when we measured the slots, it measured the lower and thicker portion of the slot. We should have also measured the top portion of the slot to see if it had closer measurements to the ones stated by SolidWorks. Since the laser cutter cuts the plastic at a slight angle and usually more than the stated measurement, when deciding measurements for designs, we should add at least a 0.05 in or 2 mm buffer region for the laser cutter.

We then measured tight fitting slot and peg.The slot was 7.04 mm by 5.10 mm while the peg was 6.89 mm by 4.92 mm. The longer side of the slot and peg had a difference of 0.15 mm and the shorter side had a difference of 0.18 mm. So we found that most likely in order to create a tight fitting slot and peg, there must be around 0.15 mm difference in width and length between the peg and slot.