Introduction: Typewriter Turned Plotter
Apologies for the poorly written instructable. I don't have much time these days and was not thinking of writing one when I was working on the project.
A few months ago I made a CD rom plotter for my daughters. See attached a couple of pictures (the one with a bunch of small cartoons and the one with the blue pen) . I borrowed the idea and files from other instructables and there is nothing special about it so I did not do a write up. My 3 yo loves it but the 8 yo said it was boring because it was too small. So I decided to build something bigger but did not want to built a CNC from scratch, because of time and $.
I then found a very cheap and heavily used simple Smith Corona typewriter and decided it was going to be the base for this built as it has pretty much all I need - precise movement in two directions, using stepper motors.
I did not find anything close to this anywhere, if you find something, let me know as I want to get ideas on how to improve it. Here it goes.
Disclaimer: No good and working typewriter was harmed in the making of this project - The guinea pig was at the very end of its life before I pulled it apart.
Step 1: Choose a Typewriter
Any electronic typewriter will do, I chose a Smith Corona with stepper motors for paper feed, carriage and daisywheel movement. I first opened an old Olivetti and found DC motors and optical encoders. Because I am running GRBL on Arduino, I needed steppers. There may be CNC software that allows the use of DC motors but I do not know of any.
Step 2: Carriage Resolution
After I had it all done I realized the carriage did not have enough resolution for nice drawings. The mechanism was designed to move in large steps , i.e., when typing. I almost gave up as I had no idea how to solve this problem.
I then found a small tin can stepper with reduction gear I took from an old scanner. I do not have pictures but what i did was to take the pinion from the original motor and glue to the output gear of the scanner assembly, in effect I just added some reduction gears to the thing.
The tin can steppers on my typewriter is a 7.5 Deg, 48 steps per revolution, not enough for smooth drawing.
The paper feed however did not need any mods, it was moving very smooth.
Step 3: Software and Hardware
I am a beginner so I keep things simple.
Here is what I use:
Arduino UNO running standard GRBL (version 1,1g I think).
CNC shield with A4988 motor drivers.
A 12V power supply
Universal G-code Sender (UGS) Platform running on a PC.
Added some limit switches for safety and to be able to home the machine.
The last picture shows the GRBL settings I entered/updated via UGS.
Step 4: Z Axis Movement: Pen Up/down
I took a slim dvd rom and pulled everything apart, only leaving the frame, rails and the metal piece in between that hold the lasers.
The pictures can tell a better story than I can.
The string is connected to a small disk which originally drove the daisywheel. I just hooked up the string to the disk and then through a small pulley and then to the small pen carriage. This motor is sort of being used as a servo, i.e., it moves back and forward about 90 Degrees, pulling and releasing the string.
It would have been a lot easier to use a real servo but because GRBL is set up for steppers I just thought it was easier.
I adjusted the travel limits, etc on the UGS software so the pen moves as I need. The small spring keeps some tension on the pen.