WEEK 14: MECHANICAL DESIGN
Objectives
Group assignment:Have us...?
Finally a complete group project. The plan for this week is start building a passive writing machine, that will become automatic during next week for Machine Design assignment. For these two weeks I work with my classmates Tommaso and Giada.
--> Our Group Page with the entire project it's available HERE
The idea
For this initial step we worked together to comprehend better the argument and define the schedule and the process we will use. Looking at how to build the machine attention was immediately captured by the CoreXY technique, because it's cool and very flexible.
In particular we found two videos on YouTube (Link Video 1, Link Video 2) that struck us and led us to follow this technique.
After that we produce an ugly sketch on paper and Tommaso a more pretty 3D model on SolidWorks, in order to comprehend better what elements we will use.
So the BOM is:
| Components |
| 2x MXL pulleys (20 teeth) |
| 1x 3m GT2 2mm belt, 6mm step (we need around 250 cm) |
| 2x iron bars 30 cm, 8mm diameter |
| 2x iron bars 28,5 cm, 8mm diameter |
| 8x linear bearings, central hole 8mm |
| some 3D printed pieces to hold the mechanism in place |
We also start thinking about motors for next week. We decided we will use:
| 2x NEMA17 stepper motor (X, Y axis) |
| 1x H-KING servo motor (Z axis) |
Let's start working!
We divided the work for each member of the group:
Designing linear bearings
In a first moment I decided to build a simple linear bearing by my self. The bearing is a very useful object widely used in this type of application because it serves to reduce friction between two objects making rotary or linear movements. The design of a linear bearing is so simple: it's a cylinder with a central hole with some engravings along the entire length. Measures we decided was:
So I tried to search online a way to produce easily parametric linear bearings and I've found This Thingiverse Page that contains a OpenSCAD file to quick create what we want. So I downloaded it and modified to adapt it to our needs.
As you can see the result is pretty good. We need only to put inside it a little bit of fat to further reduce friction.
--> Download Printable 15mm Linear Bearing (STL, 205 KB)
Designing pulleys
In same way I produce some GT2 2 mm pulleys starting from another OpenSCAD file found at This Thingiverse Page.
This time also the result is good but unfortunately we couldn't use for our project because it loses a few steps trying it on the belt. This is probably due to the slightly expanding PLA material which does not exactly maintain the set measurements. For this reason, and because we didn't have a belt with the desired length, we decided to use a pulley without teeth and a simple but effective fishing nylon.
--> Download Printable GT2 2mm pulley (STL, 499 KB)
External Frame
FOr the ezternal frame, we decided to use plywood, cutting it with laser cutter (See Week 3 - Computer-Controlled Cutting), because it's easier and fast to design and realize. In this case I created a simple box made by a base and 4 vertical sides to allow us to mount the machine easily from above. I also made a slot on one of the long side in such a way that the paper sheetcan be inserted quickly. We used a 6mm plywood and we calculate 0.1 mm as kerf.
--> Download External Frame (AI, 74 KB)
Final Assembling
We worked togheder for the final assmebling. Here you can find a shot and a video that shows the machine in operation, manually controlled by Tommaso.
