Mechanical and Machine Design

Assignments

This week’s assignment was a group project, to design and build a machine. Our plan to begin with was to use Nadya's machine kit from the Fab Academy page, but the files were meant for a bigger lazer cutter so Villi from fab lab Reykjavík was kind enough to give us the files the had already made to fit their cutter. So our next step was to cut out the files from fab lab Reykjavík, but the problem for us was that we did not have good enough cardboard material to make the kit so we decided to design our own machine.

Concept, design and cutting

Here in Fab Lab Vestmannaeyjar we have a small CNC machine called Mantis that Frosti made when he was in the Fab academy, so we decided to make our version of that machine but as a drawing machine. We had a 12mm white plastic board laying around that we thought would make a cool material for the machine. We decided to use sketchup for this design so now it was time to start drawing. To start with we made the frame of the machine, (the walls and the bottom plate) and made the frame press fit, then we made a replica, or as close as we could get to a replica, of the motors that came with the fab academy kit, we did this to get a better perspective of the motors on the machine and to get a more accurate position on were the holes for the screws and the rotating rod on the motor. We got the position for the holes by putting the motors against the walls were they should be and right clicked on the motor and selected “intersect faces with model”. Next we made the drawing plate which moves along the Y axis and then the component which we’ll stick to the X axis and then on that component we will stick the motor who’ll be our Z axis. Then in the end we made a simple component for the pen.

Our next step was then to cut out the pieces on the shopbot, to do that we imported the sketchup files to Vcarve Pro and made our shopbot files there

Assembly

Starting with the frame, it was supposed to be pressfit, which it was to a point. Only the bottom plate had joints on every side, while the side pieces only had joints for the bottom plate. We had to add some screws to hold it in place properly. We used hot glue for holding most of the machine together. We used short tubes that fitted nicely around the aluminium rods and used double tape to hold it in place while we made sure everything was straight and it moved easily on the axis, the double tape was also useful to glue the pieces in place. We also used hot glue to attach the rotary piece for the motors on each axis. The process of the assembly was pretty straight forward and the design needed very little modification.

Wiring,programming

We decided not to use the Gestalt boards to run our machine. Instead we used a board called TinyG. Our fab lab received a few boards as a gift from Alden Hart who visited the lab a couple of years ago. We thought that is was ideal to use this USB based CNC 6-axis controller for our machine. The board supports XYZ linear and ABC rotary axes with 4 motor outputs. The board is designed for small CNC applications and other applications that require highly controllable motion control so it was a perfect match for us and the machine. TinyG has a really nice online workspace called ChiliPeppr.com. The workspace is a full-blown Gcode sender for our board. The workspace connects to the board via the serial port over the ChiliPeppr Serial Port JSON Server. It lets you view our Gcode in 3D, view the XYZA positions, perform jogging, and see advanced real-time details from the TinyG.

When we had everything in place it was time to wire the motors. The motors came with a wire header so we cut it off and and screwed the wires in place on the tinyg, not having a clue in which order they were supposed to be in. For the Z axis we had to extend the wires, using a heat gun and plastic to seal the wiring properly.

Frosti’s milling machine also used an TinyG so we looted the power cable from it, measured it to be sure which pulse was which. Then we plugged it in for the first time and got it powered on, plugging it to the computer and received an signal.

We had to install a serial port server to comminicate with the machine. It´s called Serial Port JSON Server

When we had downloaded the JSON Server we could launch it from the command line

The board was now recognized by the serial port

It´s fairly easy to control the board with the ChiliPeppr workspace and we were able to easily control our machine after a little tour around the program.

We ran into an error when we were trying to zero the axis on the machine. Instead of hitting the Set Mch Zero button we hit the Home Mch button. That error made the Z motor spin almost all the way up and the X axis went all the way to the opposite corner than it was set in before. This error made the aluminum rods on our machine to loosen along with the piece that holds the pen

This mistake was a good reminder on clicking the right buttons when you are dealing with machines! When we were comfortable with the ChiliPeppr enviroment we started to manually draw some rectangles

The first test we did was to try move one of the axes and it failed, the motors did not move at all but made noise when activated. We figured it’s receiving signal from the computer but the wires must be in the wrong order. Again checking the other milling machine trying to get some inside on the wiring, we saw that the wires were joined two and two and tried it with some success on first try. The direction of the motors were inverted and we fixed that by simply switching the A1 and the A2.

We ran into an error when we were trying to zero the axis on the machine. Instead of hitting the Set Mch Zero button we hit the Home Mch button

That error made the Z motor spin almost all the way up and the X axis went all the way to the opposite corner than it was set in before. This error made the aluminum rods on our machine to loosen along with the piece that holds the pen

This mistake was a good reminder on clicking the right buttons when you are dealing with machines!

When we were comfortable with the ChiliPeppr enviroment we started to manually draw some rectangles

Files

  • SketchUp file
  • Shopbot file for the holes
  • Shopbot file for the outlines