Arduino cnc plotter machine accuracy related

Have Patience Please

So recently I wanted to make a cnc plotter aka drawing machine. (I have few broken dvd drives which sparked this project) I have dvd drive stepper motors and those expensive-ish nema motors are out of question. Most of the tutorial video on google, they show the images are really jerky and have very low accuracy. Moreover, the working surface is as low as 4cm x 4cm. So, Questions.

  1. IF I am to use a long-fine threaded screw with a nut attached (such as long threaded screws - Google Search ) and tinker with the code a bit to adjust, wouldnt it give me more space along with better precision ( finer threads)??

  2. This ones a bit confusing, by nature, cd/dvd would require A LOT OF precision to read/write data. And the mechanism seems to do a fine job. Why is it that when this is used as a cnc device the precision is diffrent?

  3. Am I on the right track? I mean is precision of the pen dependant on the thickness of the screw thread?

  1. yes
  2. The CD head follows the data track in a closed loop system.
  3. Precision and repeatability is a mechanical problem. Your solution will reflect your mechanical skills.

Please guide me here a bit.

I cant code much.. But still, the codes i saw and checked online mostly show no regerds to the steppers threads, it only just considers steps. So does it mean that finer threads would allow me to use syeps accurately?

And

How can just driving mechanism difference provide so much of a difference? Isnt the stepper motor built with certain number of steps? And if i am to implement a closed loop system (e.g use a rotary encoder to get feedback) would it give me better precision than no.1 without increasing difficulty too much? Or provide much benefit over a non-feedback system?

And i have no idea how i would make the arduino respond to the encoder... (At this point i am running out of arduino pins. ( 4*2*2 for motor and encoder perhaps?)

With stepper motors the motor moves by a fixed angle with every step. The linear position depends on the rest of the construction. No encoder required for tracking the position, but a home switch is required for obtaining the start position.

You need to figure out how many steps there are per millimetre of movement by measuring your machine. For example an M6 thread has a pitch of 1mm so one revolution would move the nut 1mm. If you were using a regular stepper with 200 steps per revolution that would give you 200 steps per mm or 0.005 mm per step. You have not told us how many steps your motor needs for 1 rev.

If you design the system so that there is no load that would cause the motor to miss steps then there should be no need for an encoder. An encoder will make things a lot more complicated. Most 3D printers and small CNC milling machines work without encoders.

I suggest you set up a simple demo with one motor rotating a screw so you can get a feel for both the mechanics and the programming.

...R Stepper Motor Basics Simple Stepper Code

  1. This ones a bit confusing, by nature, cd/dvd would require A LOT OF precision to read/write data. And the mechanism seems to do a fine job. Why is it that when this is used as a cnc device the precision is diffrent?

Because on the DVD there is the read head, and that has a voice coil on it that can change the lenses angle by small and accurate amounts, to lock onto the correct track. A feed back loop with the data keeps changing this voice coil to keep it on track.

The stepping motor only gets you into the correct region, which why it is a normal D.C. motor on many drives.

Thanks ❤. Ill return after basic construction of the project.