Basic CNC

One thing not mentioned (unless I missed it....sorry if so) is what I know as a Post Processor. Short form: Post. Not the same as P.O.S.T. for all the PC nuts here. Is is a simple translation program that must be custom tailored to each machine control type. Some controls don't read every M and G code the same, or some not all the same set. So, if you have a certain control, say, a Fanuc 0T (oldie, I know), you have to run your code AFTER (hence the term post...) writing it, whether manually, or with some CAM assistance, to actually "fit" the control on the machine you want to run the program on. You can have the same basic source program, and multiple post processors make it compatible with any control you have. Some of this will not apply to home-brew CNC, but factory but controls require this treatment.
 
Re: Basic CNC - a compilation of info.

I've been looking over this thread and it contains a lot of useful information but it is kind of scattered around. I'm putting together a (hopefully) coherent description of a lot of CNC basics on my web site at:

lobocnc.com/chapter1.html

I currently have brief chapters on motor basics and types of motors and am planning chapters on motor controller electronics basics for the different types of motor controllers, and a final set of chapters on software (G-code interpreters/machine controllers, CAD, CAM).

I'm trying to keep it succinct and tailored to CNC applications. Before I get too far into it, I'd love to have people take a look and give feedback (more detail, less detail, less boring, etc.). Hopefully you'll find it useful.

Thanks, Jeff
 
@Tony Wells: For AlibreCAM (the only package I have any real experience with), you get a ton of post files, including one for LinuxCNC (though, it's labeled Sherline, because Sherline uses LinuxCNC), and one for Mach3. I'm assuming other CAM packages are similar.

@LoboCNC: I didn't look through everything, but it looks like you have gotten a good start.
 
Re: Basic CNC - a compilation of info.

LoboCNC said:
I've been looking over this thread and it contains a lot of useful information but it is kind of scattered around. I'm putting together a (hopefully) coherent description of a lot of CNC basics on my web site at:

lobocnc.com/chapter1.html

I currently have brief chapters on motor basics and types of motors and am planning chapters on motor controller electronics basics for the different types of motor controllers, and a final set of chapters on software (G-code interpreters/machine controllers, CAD, CAM).

I'm trying to keep it succinct and tailored to CNC applications. Before I get too far into it, I'd love to have people take a look and give feedback (more detail, less detail, less boring, etc.). Hopefully you'll find it useful.

Thanks, Jeff
Click to expand...
I think your machine is great, If is possible for you to set it in the Market for a fair price accesible for students, you will detonate a enthusiasm for more hobbiest and people to get into machinning. Great Job.
 
Hi all,
I've come to this thread late, but here are some more sources of info that kept me on track for my build.

http://lcamtuf.coredump.cx/gcnc/ the Guerilla guide to CNC machining.


Alan Marconett KM6VV http://www hobbitengineering com (has new website, prob to avoid being linked to middlearth.)
http://www.marconettengineering.com/
View attachment CNCforHobbyists.pdf 5000 ft view roadmap. He doesn't seem to have it on his new website.


http://visualsizer.com/tag/stepper-motors/ this guy wrote the book on stepper motors.

regards
Andrew Burchill
 
joe_m said:
I'm still trying to figure out what I need to do for CNC, but I think I can answer the stepper motor question.
A regular motor just goes round and round (or back and forth if it's a windshield wiper motor.) A stepper motor shaft goes round in steps or increments. It takes a pulse of power and the shaft rotates a set amount. That amount doesn't vary - one pulse of power and it moves one step. The step might be 1/10 of a full rotation, 1/4, 1/3, whatever - but it will be the exact same each time. And since CNC relies on the computer moving the x/y/z axis of your mil or lathe in very precise measurements you need a stepper motor.
For example: Your computer program says "move the X axis .01 to the left before making this cut" and if your stepper motor is geared up to the x axis in such a way that each pulse of power makes it rotate just enough to move .005 then the computer will tell the motor to take two steps.
With a normal motor you get on and off and you just can't control the on/off precisely enough to get the controlled movement you need.

That's my understanding of stepper motors.
Joe
Click to expand...

I'm coming in late here, but I see a few slight misstatements in the explanation of why a stepper motor is different from a regular DC motor.

The misstatements are that steppers take in a pulse of power and move one step.

That is only true if you consider the stepper motor drive to be a part of the motor.

The drive is what takes the input pulse(or step) and converts it to what the motor actually needs-which is more complicated. It consists of applying/removing power to/from the proper windings to actually move the motor, and when the move is finished, keeping the power applied properly to hold the motor in place. If you just "pulse" the power to the motor, it may move, but it will not stay in position after the pulse is finished.
 
What about limit or home switches. What are their restrictions? My mill came with limit switches on x and z. Can they be used? If I need to buy new ones what am I looking for?



Thanks,

Dave
 
What are you using as a controller? What about interface hardware? These will both effect what you can do with the switches. For LinuxCNC, all you need is some spare inputs. Then you attach the sensors to the inputs and configure the software.

Keep in mind that home and limit sensors are used for 2 different things. Home switches allow you to locate your position relative to the machine after a power up. Limit switches are a safeguard to keep you from moving an axis too far (and possibly doing damage).

If you can tell us more about your setup, we can provide more guidance.
 
Thanks DMS,
I have a C10 parallel controller, 2 640 oz steppers with 5056D drivers from Automation Technologies for X and Y and a 1805 oz stepper with 11080 driver. The computer is an older 2.1GHz that dual boots between LinuxCNC and Windows XP with Mach 3. I'm leaning towards Mach because I like what I'm reading about Mach 4 and would like to move to USB or Ethernet as budget permits.

I guess the question really is, what am I missing to get this G0755 off the ground?

Thanks,
Dave
 
I started with the C10 and Linux CNC. Ran for about a year like that before I upgraded to some controller cards from Mesa.

The main issue with the C10 is that you are really limited on inputs (5 inputs if you use the configurable pins as output, which is what you have to do for a 3 axis machine). To give each sensor it's own input, you would need 9 (2 limit sensors and a home switch for each axis). What I did (and what you will have to do) is to run multiple sensors into the same input. I think I gave each home switch it's own input, and then all of the limit switches went into the last input. It works fine, but when you hit a limit, it is not that clear as to which one you hit, and you have to hunt around a bit.

As far as getting the machine running, I would worry about your motors first. Get things moving first, then set up your switches. Limit switches are great, but they can be a pain when bringing things up, as things may suddenly stop on you making you think something broke, when in reality, the software just faulted out.

One last thing, make sure that you wire your switches up so that they are fail safe. This means that if the wires leading to the switches is damaged, or if they are totally disconnected, the machine should not run. If you do not do this, then the switches won't really do anything other than giving you a false sense of security (meaning they won't save your bacon when it counts).
 
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