[Shamanjim]

Hi all! New forum member, nooblike, go easy!
Righto, I just bought my first CNC machine, fully assembled and ready to go, and it arrives in a week or so.
How exciting!

I have a few cad packages that I use, and producing the G-code isn't a big issue, but what I dont understand/having trouble with is this...

I generate G-code that gives me a 0-0 register on the x,y corner of the block i'm wanting to cut. And hey, that cool. However, how do I tell the machine that I want the 0, 0 to register somewhere else, (in case i want to start from the middle of the machine.) Do you move it on the CNC itself (are there buttons or knobs or something) or do you use a program to do it? (I think this is more probable) Can someone tell me how to set a 0, 0 register or what program to use to do it.
This will be my first real good look at a cnc machine, so please lend whatever advise you can.
THanks dudes, peace.

[Phil Gravett]

You can set the Datum as the 0 0 position is called in any position when you initialise machine. You can do this with software or machine but the computor has to know where this point is.
All positions taken from this point= Absolute
All positions taken from new point= Incremental.
I find absolute easier to understand, I always get in a mess using incremental. Hope this helps. Phil Gravett (Philcraft)

[beege]

What controller did you get with the machine?
Answers will vary, depending on the machine.

G52 is a "child coordinate" system, which is defined by a distance from the original system and is canceled by a G52 X0Y0Z0
G92 can assign the current position to any coordinates you want, just be careful how you use it.

A work shift offset will adjust where the origin is on ALL work/fixture offsets
G54 thru G59 are Work/Fixture offsets and can be adjusted to wherever...

Again, it make a difference what control you use.

Let us know what you find.

[ericandmollie]

Hey Shamanjim,

There are two different zero points, also known as Zero Point Offsets, or ZPO's that you need to be familiar with. The first is Machine zero. This Zero Point is usually located in one of the corners of your table for the X and Y. The Z zero point is usually on the upper limits of the Z axis. When you turn your machine on, you need to "Home" all the axis on your machine. When you home, then machine will first slide all the axis to there limit switches to find out where the ZPO is for the machine. The second ZPO that you need to be familiar with is Work Offset Zero Point. This is the zero point that your computer sets for you on your part, depending on where you draw your part on the CAD program. It is good practice to keep your work ZPO in the lower left corner of your part. If you are milling a circle, then the ZPO is easiest in the center of the hole, in case you need to make edits on the machine program. All the dimensions of the part are based off that work ZPO. Your CNC program will label the offset you are using as G54, or G55, or G56 and so on. your machine should have a place in its software labeled "work offsets" when you go to that location, it should have places to type values in for the X,Y,Z offsets. Lets say your machine ZPO is in the lower left corner of the work table, and you want to place your work block in the center of the table and clamp it down, then you would find the distances from the left side of the table to the left side of the work block, then enter that value in the work offset location in your X offset on machine, then you find the distance from the bottom of the table to the lower side of the work block and write that down in the Y spot, then find the distance from the end of the tool in your machine and the top of the block and write that down in the z offset on machine. Make sure your are entering your values in the same offset that your CNC program list at the beginning. Usually by default it is G54. But in large and difficult programs you may use 4 or 5 different offsets depending on how many fixtures you need to complete part.

I hope this helps. This is a really quick synopsis of ZPO's. Even after machining for 12 years, offsets confuse me every once in a while.

[Shamanjim]

Thanks guys, this was all a great help, and thanks for being nice to us new guys. The machine will be here within the week (hopefully) and I can't wait to try it out on some wings and fuselage profiles with the wing inserts cut out, nifty stuff..
Peace out dudes.
Shamanjim