Author: gphill02

Purpose: One of the goals for this summer at Bray was to find a way to help organize the material in the machine shop. We noticed the rack near the laser cutter held three disorderly piles of acrylic which were difficult to sift through to find the right piece. To fix this, we decided to create rack dividers that would show off some the of what can be done in the shop.

Design: Considering the rack was our environment, we came up with a divider that could easily clip into the rungs on the rack. Wanting at least three points of connection as well as geometric sturdiness, we decided to make steel framed triangular dividers. The process for making these involved four steps: cutting and brazing the wires, laser cutting and etching the acrylic, heating bending the acrylic into the steel frame, and joining the divider into the rack itself.

Major Resources Used

Step 1: Cutting & Brazing

The frame consisted of three wires, 14″, 24″, and a 25.5″.  After cutting the wire ends are sharp and must be deburred with a file. After bending 1 inch of the 24” over to make a loop, the last step before brazing is to sandpaper off the steel coating at the binding joints.

Brazing Components

Brazing is the process of binding two pieces metal with brass filler by torch. The three steel pieces are brazed to be connected as shown below. Proper brazing training is required to assemble.

Step 2: Laser Cutting and Etching

An acrylic plate is laser cut to internally fit the steel frame. We etched an aesthetic Bray logo on the side as well. The tabs will wrap around the steel frame by a process known as heat bending.

Step 3: Acrylic Heat Bending

Each of the six tabs are heated with a heat gun and bent around the wire, cooling and settling in a securing and binding form to the steel frame. This process has been used in at least one other summer project and shows promise as a useful skill for creating sturdy and functional plates.

Heat Gun Applied to Acrylic Tabs

Step 4: Installing the Dividers

The dividers should have extensions past all three endpoints. The first one is the hook made earlier. Installing the dividers starts with appropriately placing this hook and the rest of the body into the desired location on the rack.

Initial Top Hook

Next, the bottom two extensions need to be bent to secure in the divider. This was done by a set of slip joint pliers, groove joint pliers, and long nose locking pliers. The coil (below) around the front was difficult to obtain since there were very bad angles for most of the turns and the steel is tougher then the rack material itself.

Front Coil

Final Result

Aesthetically Pleasing and Efficient Use of Space

Holds Significant Quantity of Acrylic. Organized by Sheet Thickness and Size

Further: These racks were  successful in design and implementation. Since the dividers are close, they can hold more acrylic by lowering the horizontal force while leaning. Different acrylic inventory in the future can also be accounted for by moving which type of material is where. There are also plans for creating modular labels are on the way and which will further ease the trouble of finding just the right sheet to make your laser cut.

More of these can be made on the other shelf (or another rack!) to help store foam and wood material in the shop. The design of these dividers were made in such a way that they could be modified for other racks or spaces to help organize. If another iteration of these dividers are made, we suggest changing the reliefs to be more rounded in order to distribute pressure along the tabs’ bases. Also, if any of these dividers break, it should be easy to clip that divider out and install a new one by the same method outlined above.

The final edition of the penholder has been completed and nearly approved for commission as one of the shop training projects. In this most likely final blog post, we would like to do a brief review of the purpose of the project as well as go over a further inspection of the penholder and discuss the final outcome.

Purpose

To review, the penholder project concept was birthed as a way to give students more options for fabricating a project that gives them appropriate training with the shop’s power tools. We figured that a project is the best way for students to be trained, but we realized that there were some complaints with the old project, which was a wall hook. The wall hook was impractical as it had to be drilled into a wall for usage. However, drilling in dorm walls goes against residential life policy at Tufts. In addition, the project was also relatively dull and it also existed as the only option available for power tool certification. Therefore, we brainstormed ideas for new project ideas that were practical, creative, but also didn’t sacrifice using all of the power tool equipment, override the budget, and take too much time. Thus, the penholder idea was born.

The final penholder CAD design is shown below:

Build Process

Naturally, it is important to describe the details of the fabrication process.  The project incorporated the use of every power tool in the yellow zone of the shop. Therefore, we succeeded in our main objective – giving students adequate training in all tools. In terms of a time estimate, we didn’t keep a sturdy time count, but it was estimated the project would take about 4 hours to complete. It is also important to recognize time for errors and miscalculations, which are important as part of the learning process. Therefore, the project is a quite a bit long, but not too long to dismay students, we think.

Tool Usage Diagram

Further inspection: hindrances and benefits

We certainly like the design and practicality of the penholder. However, one aspect that gave us some trouble was the number of holes needed for the design. If we had more time to develop a better design, we would try to brainstorm a way to reduce the number on the top support; an attempt is shown below but would not securely fasten the arms with only one hole. Hole reduction would save time needed to fabricate, as well as decreasing the chance of having to redo the most intricate piece. Additionally, the penholder used more material and cost about 2.8x the wall hook.

Previous penholder design

An appealing aspect of the penholder is that there is slightly more margin of tolerance than the wall hook. Since the wall hook worked with such small pieces, it was incredibly easy to make a small error, but small errors would also be overwhelmingly apparent. Since the penholder involves working with bigger pieces, errors can definitely still be noticed, but there is slightly more room for lesser mistakes without affecting its aesthetic or functionality; this is important because most people will be able to make a functional device. We noticed that many people would complete the wall hook and they would look quite crooked and in some cases, unusable. We hope that people will still make mistakes so they can learn, but also be happy with their object at the end of fabrication.

Additionally, it may be worth mentioning that we polled some incoming freshmen about which design they prefer if they had to fabricate a project. We showed them the completed penholder and wall hook and the majority preferred the penholder. Since this was such a small sample size, it doesn’t capture the entire sentiment and tendencies of the student body’s preferences, but we just thought it their preference was reassuring. Also, it is important to understand that the wall hook will still remain a viable project for students to create for their training. They will now just have the option to do either the wall hook, penholder, or picture frame (which will be discussed in a separate blog post).

We have submitted our drawings for final review by the fabrication supervisor. We are excited that the design will hopefully be approved and ready for fabrication by students in the upcoming semester.

Other Media

Part Specifications

Lately, one of the 3D printers in the Design Lab has been acting improperly. Upon extrusion, the filament would not come out straight from the driver. Instead, the material would bend upwards, often times catching itself on the extruder or creating clumps and knots in the filament that wouldn’t stick to the bed.

We originally thought that there was a clog in the extruder screw tip, so our first goal was to replace it. Also, the extruder was covered in plastic and was missing some insulation tape, so we figured that melted plastic was interfering with the path of the filament or that the tip wasn’t heating properly which would impact the state of the material as it extrudes. Either way, we thought that if we replaced the screw tip, cleaned up the melted PLA, and added more tape, the 3D printer would revert to extruding properly. We began this process by removing the extruder from the conveyor track and preheating it so we could chip away the melted plastic. Once the driver was cleaned up we completely took apart the extruder and examined it for any issues but couldn’t find any obvious problems. From there, we removed the screw tip, which was much harder than expected. We then removed the old tape bits and added a fresh layer of tape and reassembled the extruder. However, when we tried printing, the same problem would occur.

We decided to take apart the extruder once again to look for problems with the individual components within the feeding mechanisms. Once we removed the fans and heat exchangers, we could get a better look at the gears and tubing that leads the filament into the tip.

The gear system that clamps to the filament and feeds it through to the tip seemed to be working fine after testing it. And since the tip had just been replaced and cleaned, we figured the problem had to lie in the tubing between the gear system and tip. Surely enough, the plastic tubing (which can’t be seen in the above photos) that exists in the metal frame had been clogged. We replaced this component and put the extruder back together again. When we ran a trial print, it was a success!

Afterwards, we decided to replace the bed in this printer as well. We had replaced the bed already with one of the 3D printers and the new material was much more effective at adhering to prints. Removing the old bed was a long and tedious process but once we stuck the new material to the bed frame our prints came out in much better shape. All in all, the 3D printer is now functioning very well.

We have finished sketching out our ideations and have now moved on to creating our prototypes on Solidworks. Our pen holder model looks like this:

. 

Before we begin the fabrication process we want to try orienting the pieces in different ways just to see if we can create a more aesthetically pleasing model. We will then begin making protoypes with whichever design we prefer. Also, we are prepared to make some changes to our model after fabricating, because the fabrication process will reveal some detail flaws that can only be noticed with the physical model. For example, while we have a sense of the amount of time it takes to build this, actually building it will obviously give us a better time approximate and we can make changes on the design depending on whether it takes too long or too short to build. Fabricating will also give us a better sense of material cost and if the structure will have proper weight distribution and will stand sturdy and upright.

A few things to mention with this design are that we intend to use the DIWire machine to create the support mechanism which directly suspends the pen. We spent time working with the DIWire machine to figure out the minimum segment length needed for a bend in the wire and the maximum angle that the wire can bend. We discovered that there needs to be at least approximately 3/4″ of material between two bend points and the maximum bend angle is roughly 55 degrees. This knowledge was helpful because it allowed us to draft a better and more precise model that fit the maximum parameters of the DIWIRE.

In addition, we spent time making different configurations of this model on Solidworks. By that, we mean that we uploaded the same exact parts into an assembly but tried different rearrangements of those parts. We are still working on making the second configuration of the pen holder, as it has taken some time to learn the nuances of Solidworks, so we aren’t able to upload a drawing on this post  but the other model essentially deals with rotating all of the aluminum 1/4″ stock pieces 90 degrees so they lie horizontal on the main support bar, instead of vertical. We liked this design feature, and we will continue forward with the design we prefer or we may even just fabricate both models to compare.

After reviewing the sketch pages, our team decided to move ahead with three concepts for a new shop training project – a pen holder, model car, and picture frame. The pen holder has a lot of room for design capabilities, and uses an appropriate amount of material for a training project, involves the use of all yellow machines plus potentially the use of the DI Wire Bender, and is practical for a college student. These qualities made the pen holder a leading candidate for fabrication as a training module. The model car, on the other hand, will probably take longer and involve more parts, but adds an element of fun and therefore more excitement. There is also a lot of room for extra design features for the car project, such as building a ramp, racing the cars, and posting the results on a leader board, or building a type of ripcord or torsional spring feature to launch the cars forward. The excitement of the car may be attractive to students, especially considering that one of the biggest problems with the wall hook was that it was boring. Lastly, the picture frame is another practical design that can be built to involve the use of all machines and is also slightly more exciting than the wall hook. However, the excitement that comes from the picture frame doesn’t come from the “fun element” like the model car, but rather from the design’s practicality. The other big problem with the wall hook was that it couldn’t be used in a dorm room. We figured that our new designs had to be either fun or practical or both in order to draw more interest in using the shop.

The next step was to ideate and create different designs for each of the concepts. Unlike for sketching, which was done on generic 8.5″ x 11″ paper, we used big sheets of paper to draw out our ideations. The goal here was to tune our concepts so they can be modeled and built well in the shop. Therefore, we put an emphasis on understanding the dimensions of the materials that the students will be working with, so we could better visualize and create ideations of our concepts that could be realistic training projects. We spent a lot of time drawing, but we also spent a lot of time discussing and building off each other’s sketches. We also wanted to brainstorm features that went outside of the realm of the yellow zone tools to add more flare and interest to the projects, while being careful to not stray too far away from the main objective of shop training. For example, we sketched out ways we could incorporate wire bending into the structure of the pen holder, or laser cut acrylic for the picture frame or bonus materials (axles and wheels) in the model car. However, as mentioned previously, it’s important to not make the project too intimidating because most of the students who are fabricating these projects probably have never spent any previous time in the shop.

To help with our ideations, we also made a trip to Toys R Us to do some “advanced research” which involved buying and ultimately taking apart some model cars. The goal was to understand some of the more advance features of the car and to get a better sense of how we could model these features in the shop. We had a good time in the store, retrieved some heavy data from our research, and Ben even recognized some of the products he helped design. We ended up buying a few different car models, and each model had a different acceleration mechanism. Two models had a wind back and release feature meaning that when the car was rolled backwards it would propel forwards upon release, three models had a ripcord design, in which a grooved, plastic, cord would be inserted into a rotating gear that was fixed to the car’s wheel and when the cord was pulled backward, the wheel would spin forwards. The last car model had a charged acceleration method that worked by rolling the car a few times forward while keep it secure in hand, and then letting it go after a significant amount of torque was built up.

We took apart the models and examined the interior. We first looked at the two “Cars” models, which both featured the wind-back design. After breaking off the exterior shells we noticed that both models have a very similar design for their respective systems. They both featured a gearbox system that attached to a torsional spring. A gear was connected to a torsional spring on end and attached to more gears that ultimately connected with a fixed gear on the axle. When the car was released, the torsional spring would release, spinning the gear rapidly and propelling the car forward.

Above, we can see the gearbox system that is used to accelerate the car. The blue gear connects to the torsional spring and the green gears attach to the smaller blue gear which is fixed on the car’s rear axle. It is worth mentioning that the other “Cars” model had a nearly identical gearbox.

The next models we observed were the ripcord “Hot Wheelz” cars. These cars had a grooved gear attached to the rear axle. The ripcord would insert into the slot between the gear and frame, and when pulled back it would spin the back wheel, moving the car forward.

The car had a three wheel design, with a much larger wheel located in the rear of the frame. This design is something we could see ourselves emulating, because it would be relatively easy to create the gear and ripcord with the 3D printer and laser cutter and it would be a cool bonus feature to have the car accelerate without just simply pushing it forward. Creating the body of the car could be done with the use of all yellow zone tools so students could get all the appropriate training, which is the main objective of the project. This was an idea we liked, and definitely wanted to ideate further with the ripcord design in mind.

Today, there is still work to be done to create the final models of each design so they can be designed in CAD and we can begin prototyping them. This week will be spent doing just that – designing our models on Solidworks and hopefully we can begin fabricating them in the shop. Once we actually fabricate each model we will have a much better idea of the amount of materials, rigor, and time needed to build each project.

The past two days have been spent working on the Biomimetic Mover project. The project is aimed at creating a device that is able to simulate any sort of planar movement along a flat surface without the use of wheels. Jonathan Rooney and I have spent our time trying to work on a mechanism that uses the Klann linkage technique, which is a method that simulates a spider-like gait. A diagram from Wikipedia for each position in the Klann linkage cycle is show below:

The diagram shows the linkage in the fully extended, mid-stride, retracted, and lifted position. In the diagram, the right most link with the extended pin is fixed to a gear. The gear rotates the link and drives the motion of the system.

After it was determined that the Klann linkage was going to be modeled after, we brainstormed ideas about certain design features. After a lot of thinking, we came to conclusions on the first prototype. We then used the software package OnShape to design the links and frame to match our sketches and plans. A few of the links are shown below:

Link drawings on OnShape

We then uploaded the OnShapes .dxf files into the laser cutter and cut our pieces out of 1/8″ acrylic. It is worth noting that the design of the links and frame are something that have remained consistent throughout our entire design process.

Once we had our components, we thought more about how the legs are going to work in tandem to create the desired walking motion and made some changes along the way. We stand today deeply engaged in the building stages, with a goal to create an eight-legged mechanism with two vertical, hexagonal frames, and a gear assembly. There is a pair of legs on each end of the frame, with each leg attached to a gear.  The gears are connected to each other with a threaded bolt and the two legs are connected to each gear with each connection 180 degrees apart. So when the gear is driven, one leg will left up and the other will touch down. This happens in tandem with all of the four leg pairs, so hopefully if designed properly this will create the walking motion.

These pictures show one of the linkage systems connected to the mounted gear. Also additional leg structures, bolts, and spacers are shown. All of the link pieces, the gears, and the spacers were laser cut.

We have encountered some problems along the way with spacing. We have had to figure out ways to space the linkages so they can flow well as the gear spins. Countersinking the acrylic frame and gears, laser cutting custom spacers, and using various bolts of different lengths have all been methods we have used to ensure the system can work. We also have had issues with hole sizes because we have had to change bolt sizes often, so we’ve have to recut many pieces.

The video below demonstrates how driving the gear generates the motion of one of the legs. Instead of my hand, there will be a central gear which connects to another gear on the other end, making a three gear system. This will occur on the side of this frame as well, and then it will be symmetrically reproduced on a second frame, totaling 12 gears. The two plates are connected and hopefully we will have a functioning biomimetic mover.