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.