Questions For Machinists

[USAPatriot]

I have some questions for machinists and/or engineers. I'm in no hurry, don't want to lay it all out at once since it's rather involved but the first question is simple, I hope:

In CNC machining, what is the computer/tool using to reference where it is, where it's been and where it needs to go?

FWIW I actually joined 3 machining forums before bothering anyone here with this. On one, my membership was denied, the other two my membership was cancelled shortly after I posted this question. Trade secrets? Closed clubs? WTF was THAT all about? Very strange. -Rod-

 

[WayneShaw]

I can't answer your question about CNC machines, but I am curious about which forums gave you the boot. I frequent several myself and haven't had trouble......yet.

 

[Rustystud]

USPATRIOT:

CNC programs work in what is called G-code. G code is written in a linear fashion simular to computer basic,line numbered IE: 10, 20, 30,...). G code uses cartesian cordinates to locate from a known begining cordinate. When you start you initialize by send your tool to a know starting point. You line up your mateiral to be machined at that same starting point. It uses computer code to direct the tool path,including tool speed,feed rates, and trig functions to determine the height and length or arcs, or entire circles. Tool geometry also plays into the machining equation. Some machines work in single planes, others work 2,3,4,and 5 axis. There are some really great window programs that allow for CAD,computer aided drawing) drawings to be converted to CAM,computer adided machining). The background code is again G code. These programs allow for tooling and solid modeling,3D simulation). I was trained on Gibbs Cam, there are several realy good programs. There is an entire forum on Home Shop Machinist and Practical Machinest web Sites. Neil Knopf is the moderator over there. If you are treated badly at either of these sites contact him at the Village Press. He does not put up with any bad conduct. He has an e-mail address on both of these aforementioned web sites.

I had one semester in CAM logic, IE: writing G code.
The following semesters were learning GIBBS CAM.
I had one semester in 2 1/2 and 3 axis machining.
I had one semester in 3 axis machining.
I had one semester in 2 axis turning.
I had one semester in 3 axis turning.
I had one semester in 2 axis plunge EDM
I had one semester in 2 axis wire EDM
The list goes on...

Machining has made great advances but much of the artestry has been lost to mechanization. There are things that can be CNC machined and there are things that still can only be manually machined.
Rustystud

 

[JimmyO]

If your product is machined in a fixture there are usually tooling balls inserted in the fixture that the CNC uses for axis reference. I use CATIA but it's usually too expensive for a home shop user. Mechanical design, using CAD, Fixture design,something to hold your parts while being machined), Tweaking auto-generated code for speed), CNC operation and being an actual machinist are many worlds in themselves.

You might want to lay it all out at once so someone can give you an encompasing answer.

FWIW if I wanted to know more about machining I would take classes @ CC or find a machinist and work for lessons. If I wanted something designed in CAD and didn't know how I would find someone who does know how, unless you really want to invest 100s or 1000s of hours in the art.

If you need help with designing parts or tooling that are not so complicated,relative) I may be able to help you,read free)in March.

I was contemplating trying to learn to program controller ICs so I can interface the chargemaster dispenser with the vic-123, I've got a friend in LA that can do it in a day or two I'm sure...What was I thinking?

Anyway sorry for the long post and good luck with your interests!!!

 

[kampfeld]

I'M not sure if the other guys answered your question,or you were looking for how the machine knows were it is at.
On the end of each ball screw that controls each axis their is a encoder that keeps track of rotation of the ball screws end feeds back to the controller that information. The controller then interprets the information and feeds each servo with power and coordinates the axises. Some machines also use glass scales. I think this is basically how it works.

 

[usngunner]

I'M not sure if the other guys answered your question,or you were looking for how the machine knows were it is at.
On the end of each ball screw that controls each axis their is a encoder that keeps track of rotation of the ball screws end feeds back to the controller that information. The controller then interprets the information and feeds each servo with power and coordinates the axises. Some machines also use glass scales. I think this is basically how it works.

That is correct. There are several types of encoders and postioning systems.

The simplest is a linear reference type. The machine has a "Home position" usually referenced by a proximity switch that the machine finds when referencing and plugs in the calibration value. The encoder, be it rotary style or linear glass,both do the same thing, just different styles), counts up or down from the reference position and works relative to the home point.

The other is an Absolute Encoder, and it in conjunction with the control "remembers" it's actual position at all times, eliminating the need to home/reference the machine.

Both have their advantages and disadvantages.

The code running in the control sends the desired position to the control, and it calculates the direction and speed to move the machine to get there. Then we get into error, ist, step, and all kinds of esoteric stuff to make it all work. Hence the price of a CNC control.

That's pretty simplified, but it covers the basics.

 

[USAPatriot]

Thanks for all the replies. USNgunner answered closest to what I needed to know but there's much I don't understand and much I'd like to.

Trouble is, frankly, if I say too much, the subject of my thoughts will undoubtedly wind up on the store shelves with someone elses name on it. That's not a body slam against anyone, it's just human nature, I'm afraid.

I'm not mechanically inclined, have zero math skills, couldn't program a VCR if my life depended on it...so I'm totally unsuited for this work, but I know what I want to do, just not how to do it. Living hand-to-mouth on SSDI doesn't help either. I'm sure I could work up a crude servo and ________ and a ______ to run this but I'd have no way to control it, and that's the real problem.

The application would be limited. No one would become a millionaire over it since obviously the technology already exists to do it. I'm just looking for a way to get it done without ending up holding an empty sack. I'm open to ideas on that score. -Rod-