Basic CNC

Billy G,

Ok, I'll give it a shot where I would like to see this go (on a 5k ft level)

1. Types of implementations:
A. Lathe type CNC
B. Mill type CNC (i would include the home built CNC router type solutions).
Roger

To that list you could also add, plasma cutters, engravers, hot knife machines for cutting polystyrene, probably 3D printers, and possibly even more esoteric machines like robotic arms (which might be fun to have on one of the other machines as a 4th axis for picking things up and moving them around).


M
 
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good point, my thinking was to categorize it based on how the cnc moves (and feel free to correct if I have this wrong):

how about this categorization?

2D - CNC lathe (i don't know how to classify those that can change the rotational speed, help?)

3D - CNC mills, plasma cutters, hot knife,engravers and laser cutters, 3d printers (not sure if its 3d, as there is a 4th stepper to control the material feed rate)

4D - advanced CNC mills, robotic arms

5D - ?? I've seen it mentioned..

thanks,
Roger
 
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I take a stab at Rogerrabbit's outline

Ok, I'll give it a shot where I would like to see this go (on a 5k ft level)

1. Types of implementations:
A. Lathe type CNC
B. Mill type CNC (i would include the home built CNC router type solutions).



A. how do they work? (basics right? )
CNC is Computer Numerical Control. According to wikipedia

Numerical control (NC) refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to controlled manually via handwheels or levers, or mechanically automated via cams alone.

So, we are using a computer (and software running on that computer) to control a machine tool. That could be any of the items listed above. LinuxCNC will control up to 9 axes. According to their website, Mach3 will do up to 6 axes. Axes are points where the machine can moved. Think X, Y, and Z axes on a milling machine. Given that, all types of computer controlled machines operate the same more or less.

B. what are the differences?

Number of axes, work envelope, material, type of operations capable.

For example, a CNC lathe, just like a manual lathe, is going to produce cylindrical work, and a mill is going to produce prismatic work. We can blur the line here, but in general you are going to use a CNC lathe for the same thing you would use a manual lathe for, its just that a computer is turning the knobs based on instructions you gave it, rather than you actually turning the knobs by hand.

Some other examples

- CNC Router/gantry router. These are basically milling machines. They tend to have really large work areas in the X and Y, and relatively small Z work envelopes. Usually they have small, high speed spindles (routers are common), and are used on wood or plastic, but sometimes aluminum. If you are into woodworking, want to make signs, or quick prototypes out of plywood, or mdf, this is probably the machine for you.

- Hot wire cutter. Are you into model planes? I'm not actually sure what else you would use a hot wire cutter for... anybody else?

- Plasma cutter. Are you a welder? Want to make custom metal work? This may be for you. They tend to have similar stats to a gantry router, except that instead of a high speed spindle, they use a plasma cutting nozzle. LASER cutters would be more or less the same, except using a laser instead of a plasma nozzle. Waterjets too.


C. If I am new to the CNC world, which type should a start with assuming I have either both a mill and lathe or neither.

I would say, figure out what you want to make, and then get the machine that will let you do that. Mills are probably the most common and versatile, but if you want to make large things, a router would probably suit you better. If you want to cut lots of sheet steel, you are going to be disappointed with a milling machine, and probably would be happier with a plasma cutter.

If you just want to explore the technology, and see what is possible, I would say a small CNC, desktop CNC router would be the cheapest route to this. 3D printers would be a close second. Both can be had for a couple hundred dollars US, and will fit on your dining room table, stow-able under the bed or in a closet when not in use.


D. for each, buy a machine, convert existing, or build from scratch?

Something like
new: high $$$, but software & machine integrate well.
convert: med $$, but kit may not be available, anyone have experience with a kit they would like to share/
build: low $, but you need to plan ahead to make sure software works with machine.

Honestly, software comparability with home built machines is not a concern. LinuxCNC and Mach3 (though I have no direct experience with Mach) are really configurable, and can do a great deal. The main things you have to consider are

1) How much work
2) How much money
3) Who do I call if there is a problem?

Everything is gonna depend on what type and size of machine you chose. I picked up a used knee mill and am converting it myself. I am probably into the project to about $3k, and I don't even have ballscrews yet. To put that in perspective though, if I had purchased a new Tormach, I would have been up to $8k already, probably more with accessories. That being said, I would have a ready made, solid machine, with lots of accessories made for it, and somebody I could call when things go wrong ;).

Now, if I had purchased a new knee mill, the price difference at the end of the day would have been basically zero. If you are going with a small machine like an X2, then you would have to do the math.

The main thing to consider is that you want to stick with the basic formula. Lathes have 2 axes. Mills have 3 (or more, lets ignore that for now). The trick here is that there is a lot of software out there (CAM software) that takes CAD drawings and produces GCode to control your machine. If you have some oddly configured machine, off the shelf software is not gonna work. So stick with the basic formula.

The other possibility is that you write the GCode yourself (it's very doable), but for complicated things, it can get... tedious.
 
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my suggestion for anyone who is interested in cnc to start small and with a mill, a cnc lathe is nice but will never be used as often. if you can master a small cnc mill like a sherline you will be a wizz with a big mill. the small mill uses small pieces of material and keeps cost of learning to almost nothing for materials. the process is exactly the same only your making smaller parts so you will be making more parts more often and mistakes cost nothing in materials. a friend of mine laughed when he seen my sherline so i drilled 5 holes through the head of a pin and gave it to him the next day. he still has the pin on his desk. my point is to see if you really want to learn cnc and if not you will always be able to get your money back on a small machine. if you do enjoy it then big parts will be easy and you use your little machine to build the parts for your big machine. the parts made in the pic were done on a sherline cnc mill and cnc lathe.
steve

DSCF0433.JPG
 
Hummmmm great idea.

This consept of a place for people that are intrested in the basic's of a subject s fantastic. Following what I have seenso far i see a common problem with open discussions on a spacific topic. Some one asks a simple question then diferent people ,with diferent levels of knowledge or experince respond at what they preserve as "BASIC".. then the topice gets runoff in many diferent directins. never fails...:))

But that said, I still found some informitive info here and would like to see this thread turned into something useful to thoes that are intrested in basic info on the subject of CNC..

I think we need three modirator volunteers to make this work. or mabey 4. one with advanced knowledge of a subject, one with a good workers level of understanding, and a student level person to tell when the real basic answer has been reached. and finally a major overseer to collect answers to a spacific topic and post them in a seperate file that others seeking the answer could go to and see the cleaned up version.

When a question comes in the modirator could eithed open a new discussion or point to an already answered file.

i have several basic questions, or at least what i think are basic, the guy next door might think as advanced and the guy over at palmer machine think as below basic.:thinking:

any whooo keep up the good work

larry
 
.........................................i have several basic questions, or at least what i think are basic, the guy next door might think as advanced and the guy over at palmer machine think as below basic.:thinking: larry

I'd say go ahead and ask your questions Larry, even if it's as basic as "What's CNC?"

There are no dumb questions on this forum. ;)


M
 
I have started reading this thread and a question came to mine. If a brushless motor that powers the spindle on my HiTorque mill is basicly the same as a servo motor, it brought me to thinking.

In CNC motion of a machine, why could you not use a stepper or servo to control the spindle on the mill? I mean, in my thinking, it would be prudent to have a spindle that can go both directions instead of just counter clock wise. To effect, if the spindle can go either way with the same amount of power, then in essence, you could have the cutter always in a climb cut no matter which side of the part it may be on.

Make sense?
 
On "real" CNC milling/machining centers, the spindle is under the controller's command. It set's the cutter surface speed and direction. Additionally, if the feedback encoder and control allow it, and most do support this, it will do what is called "rigid tapping". To do that, the spindle RPM, Z axis feedrate and position are all programmed to follow the tap's lead, stop at the (hopefully) bottom of the hole in blind tapping, and reverse and back out. And even then, go back in if you need to clear the chips and go deeper.

It is common practice, and generally preferable to up-mill, or climb cut. This takes advantage of the very low backlash of the ballscrews normally seen on CNC machines.
 
Hi Doc,
Ok heres one for you.

i have my sheen set up and running, i'm using moch3 updated with the mochmill pro software on a piter with windows XP, through a CNC4U C11 breakout board controling 5056D drivers to the largest steppers in the nema 23 size.

on the drivers are a set of switches that 1. controle current 2 controle microstepping. in reading the manual it appeared to me that setting the microstep switches to all on set things up such that mock3 was setting the steps per rev.

so now having read here and in the CNC home threads what is the story with the switches vs the computer for microcontrole??
Larry better known as Docwishbone:))
 
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