The Home Machinist!

There seems to be some misunderstanding about what 2 1/2D can do. I use Sheetcam and Mach3. All three axis are under program control and the Z axis can position to many different depths without my intervention. You just have to define a new process for each level or layer you are going to cut. And as long as your work can be done with one cutter you can start and walk away. What you can't do is a profile unless you cheat by using a profile cutter. I use tapered and ball nose cutters all the time.

John

Oh yes
I forgot, Mach3 will do 3D

no misunderstanding.

your 2-1/2D limitation is software, not control....2-1/2d software is very common.

Surfacing takes another entire level of sophistication

We have been discussing (i thought) the definition of a 2 vs 2-1/2D control definition.

I own a 2-1/2 axis machine and that's not the case. What you describe is actually a two axis operation. There is no control or input/ output for the Z axis (other than CNC unrelated dro). The stop/ prompt is triggered by reaching the anticipated XY position on the table, which has nothing to do with the Z axis other than labeling, and then awaits operator input to continue.

A true 2-1/2 axis machine does have LIMITED control of the Z axis. My machine will drill multi-hole patterns, peck drilling and any other Z movement requiring moving the Z axis to a specified depth without my help. With full 3 axis control you can do contouring, thread milling, etc. which I cannot with my machine since those operations require the simultaneous movement of all three axes. Although I'm toying with the idea of powering my knee (with weight compensation) as the Z axis for the missing capabilities and using the existing powered quill for drilling operations...

What you are describing is a 3 axis machine but not a 3 axis SIMULTANEOUS controller.

No, it's a 2-1/2 axis machine. I could easily update my control system to full 3 axis capability but the machine wouldn't benefit from it. There have been several mentions that the control electronics/ software are the only differences between a 2-1/2 and full 3 axis machine. While that might be true in a very few instances in most it is not.

My 2-1/2 machine has the Z axis driven by a timing pulley attached to the quill handwheel. While this setup is adequate for X-Y stationary drilling operations since the Z axis position is looped back to the controller via the Z dro scale. The quill moves to the specified depth and then immediately retracts. Z axis backlash isn't an issue in this scenario. However backlash would become an issue with this setup if you attempt to hold a critical depth because the quill (Z) would float up and down at will in the amount of the backlash.

True 3 axis CNC's usually incorporate a ballscrew on the Z axis which has little (if any) backlash and keeps the Z axis true to a given tolerance depth at any given point while under control and in motion.

So software is not the only difference between a 2-1/2 and 3 axis CNC in most cases. Hardware plays a definitive roll as well. Since most manufacturers of 2-1/2 axis mchines also made 3 axis models it wouldn't make much marketing sense to offer an identical piece of iron with a "light" software package at a considerable cost savings. The hardware is what makes it a true 3 axis. The software merely takes the additional hardware to its' full potential.

what do I know, I only write CAM software for a living....

what you have is some sort of hybrid that doesn't fit into one of the standard definitions used by the biggies of the industry...

FLtenwheeler:

First: you need a CAD program to make a drawing. Any CAD program that can export a DXF file will work. Correct? You do not need CAD. You can write your own programs in Microsoft notepad.

Second: you need a CAM program to convert the CAD drawing into G code.
Does this program talk to the machine or do you need a driver program?
You do not need CAM software. You can write your own programs in Microsoft notepad. The CNC machine
Language is G-code either written manually or CAM generated. You will need a program to actually run the machine. I use Turbocnc a $20 program or you can use MachIII for $165

Third: you need motor drivers (little black boxes) for the type of motors you are using. Stepper or Servo.
Am I right in that all servomotors have a feed back function? Closed loop.
To build a CNC system you need a machine, a computer, a breakout board to connect your computer to the CNC controller, you need a DC power supply, driver boards for each axis, Stepper motors or servo motor. You do not have to have feed back

Fourth: you need motors that will provide the motion on whatever type of machine you are using.
Yes, steppers or servos

Below is a link to my Bridgport retrofit. For what I do working from my garage this thing is perfect. Someday I would like to build another retrofit using servos with feedback and all that stuff. But, I make money with what I already have. I did this retrofit when I was 55 years old. Old dogs can learn new tricks
http://www.outbackmachineshop.com/CNC.html


Jim

_________________
Tool & Die Maker/Electrician, Retired 2007

So much to learn and so little time.

www.outbackmachineshop.com

Gents,

All the controls used to be a 2 1/2 axis control at best. Industry definition was 2 axis simultanious, 3rd axis shared. All three axis could be programmed, but only 2 could interpolate at the same time. You could machine a 3d slot if it used the x or y axis with the z, but not if it required all three axis to move at the same time. You could mill an arc using any two axis, but not an helix, that required all three axis to move. The first true 3 axis simultanious that came out created quite a buzz at the 1980 Westec show.

Modern machineshop had an article on constant z level machining in the late 80's for shops with 2.5 axis machines who were trying to do surfacing.

Bill, and example of a 3 axis control that could not move all three at the same time is the Bandit control, but all 3 axis before 1980 were that way. A 3 axis knee mill with the bandit control in 1980 cost $45,000. The same mill with the 3 axis simultanious control was $60,000.

Sorry to be so slow to comment on this, but time constraints have limited the amount of boards I had time to read up till now.

Regards,

Doug

_________________
http://www.precisionlocomotivecastings.com/
Building a 70 ton Willamette in 1.6"
Building a 80 ton Climax in 1.6"

"Aim to improve!"
"Mine is not to question why, mine is just to tool and die"

I seem to remember programming 3 axis linear moves on an old K&T Gemini back in the middle 70's, so I think that your time-line is probably a bit inaccurate, but then we all are getting a bit overwhelmed these days.

The Fanuc (General Numeric) 3000 would execute a 3d XYZ move - I know this because of many a tool crash from people performing XYZ tool changes and performing 'kamakazie' moves to the work to save time - and destroy clamps.

Even the old GE 550's and 1000's would do 3 axis XYZ back then, but the Cincinatti Milacron 'Big Blue' controls would not, so it was a mixed bag from mfg'r to mfg'r...and programmers would get caught forgetting about it from one machine to the next.

3D arcs (helix) are still not standard on many machines. Fanuc still sells it as an option on many controls.

Even today, there are only a few controls that will perform 3D arcs using coordinate systems other than the XY ZY ZX planes using coordinate transforn algorithms. Otherwise, the arcs have to be chopped up into little lines and executed as linear moves.

I always thought that if it would do helix's it was full 3 axis control, anything less was 2 1/2. When I was learning you got a fine for doing a tool change without lifting Z first.
Regards,
Gerald.