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Can I change the distance the axis move per motor turn on a homemade CNC machine? Answered

Currently, I really want to make my own CNC plotter. I want to try a different approach so instead of using pulleys or threaded slider to move the axis, I'm planning to use 3D printed rack and pinion to move the platform. I will limit the movement by using drawer slides.

However, the thing that bothers me the most is that can I calibrate the movement of the stepper motor to move exactly a distance I want? I mean if the gear's perimeter is 2cm, then 1 turn on the motor will make the axis move 2cm, definitely different than using pulleys. Also, can I convert PCB prints from eagle to Gcode to control the plotter? (my goal is to make a plotter that can make PCB)

I'm sorry for the lack of picture. I want to make sure that my project is possible before I start doing it.


P.S.: Is this a good idea? Or is it much better to mod my 3D printer into a plotter? I'm planning to buy a Monoprice mini printer fyi. 

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rickharris

Best Answer 2 years ago

You will be able to move he stepper a minimum of half a step, how many degrees that is should be printed on the stepper typically 1.8 deg so 200 steps to a full rotation.

The use of rack and pinion is done, often using a standard aluminium timing belt pulley (cog) and a timing belt fixed to a stationary base. so that the stepper is mover along the belt which remains stationary.

This is likely to be less trouble than printing parts.

There are about a million things that will control the success of building CNC machines.

Stiffness of the system, backlash, enough torque in the drive system, friction, software, accuracy of build and many others.

Generally your calibration is done in the software. Your looking for 1 mm on the drawing to be 1mm of movement +/- at the cutter. As your 2 cm circumference pulley will only have a diameter of 0.63cm getting it on the shaft of a reasonable sized stepper is going to be hard!

You need to have a good look at what others have done. that way your going to get some idea of what can be successful.

There are lots of CNC projects here if you try a search.

http://www.maslowcnc.com/

is interesting if you want to work on a large scale.

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rickharrisrickharris

Answer 2 years ago

Having use CNC machines from lathes, router and laser cutters over the years I have some doubt as to their worth for the DIY user. You simply don't use it enough to warrant the cost.

This, however , IS a useful tool in that vein ate a very reasonable cost to build.

https://www.instructables.com/id/3D-Router-When-a-C...

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Shizenrickharris

Answer 2 years ago

Thank you. My design is very small, so I think this motor is enough https://www.amazon.com/Elegoo-28BYJ-48-ULN2003-Ste...

As for the rails, they haven't arrived yet so I can't tell how wobbly they are, hoping not too much

And yes, I messed up my calculation, instead of the circumference, I got the area of the circle, that's why I think it is possible... Now if the circumference is 6cm, then 1 step is 0.3m, is this enough accuracy for a PCB?

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rickharrisShizen

Answer 2 years ago

Still something wrong here 6 mm circumference is only 1.9 mm diameter MUCH smaller than the shaft of most CNC system stepper motors.

Circumference is round, diameter is across.

Circumference will be 3.142 x the diameter.

I trust you mean 0.3 mm - other wise your way off.

A lot depends on how small your tracks and track separation is going to be.

If 1 step is 0.3 mm then your at best only going to get either 0 error or 0.3 error (1 step)

I may be wrong but I don't think a stepper only 1inch in diameter is going to have the torque to drive, I assume, a dremmel through copper PCB material.

However by all means try you can only be wrong no real danger involved.

not unusual to find CNC machines with

"An specific area of concern related to accuracy is backlash. Backlash
is positioning error caused when an axis switches direction. If the
direction of rotation changes, any lag in the change of direction in
linear motion is not seen by the system and results in positioning
error. On both our R&P drives and ACME screw based systems,
properly setup systems have very low amounts of backlash, typically less
than 0.001” in our PRO setups. To put that in perspective, that’s
about the thickness of 1/4 of a sheet of notebook paper."

https://www.google.co.uk/#q=CNC+router+accuracy

http://www.cncrouterparts.com/how-accurate-will-my...

I think you need to think and consider your design very carefully.

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Shizenrickharris

Answer 2 years ago

Sorry but I'm sure I typed 6cm and I incorrectly type 0.3m in accuracy (I meant mm). Guess we both make a mistake

Backslash is the first time I heard it, I'll look into it more, thank you

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rickharrisShizen

Answer 2 years ago

Your right I miss read the cm/mm in my haste.

You may have to try it out as I said there are many variables involved.

Good luck.

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Shizenrickharris

Answer 2 years ago

Also, I am not milling the PCB board. I simply mark the board with permanent marker so that I can etch the boared