How do I set up part zero and tool offsets on a CNC mill?

[AccuMillGuy]

Hi, I am new to CNC milling and I have a Fanuc 3M controlled AccuMill from the 80’s. We have a person coming in this weekend to train us on CNCing but I was wondering if there is any material on the Internet on how to do the following things.

Set tool compensations & offsets.

Set part zero & Machine Zero.

The manuals and books we have primarily focus on programming and has little to no info about setting up the mill for running a job.

If anyone can point me in the right direction I would greatly appreciate it.

Thank You

Adam

[Geof]

What you are asking takes quite a lot of explaining; try doing a search here on CNCzone this type of thing has been discussed before.

After you have had your training come back with specific questions otherwise you are likely to get buried with too much information.

[AccuMillGuy]

The first question I have is...

I am milling an Aluminum block that’s 6" x 6" with a 0.5" End Mill. The block is 1" deep and 0.5" of the block is sticking up from the vise.

What part of the block do I place the End Mill on to set part zero for X & Y? In my CAD CAM software the left top front corner is part 0.

Thanks

Originally Posted by Geof What you are asking takes quite a lot of explaining; try doing a search here on CNCzone this type of thing has been discussed before. After you have had your training come back with specific questions otherwise you are likely to get buried with too much information.

[Geof]

You need to use the same reference point in the machine as you use for the drawing; in your case the top left front corner.

This means you have to find the X and Y coordinates for this corner and enter them into the G54 work offset table. One way to get the coordinates is use an edge finder on the sides of the piece; your Trainer should be able to show how to use an edge finder.

The tool offset is set to the top of the part. There are various ways to do this but the most direct is to bring the tool down to the part. I use paper between the tool and part to find out when I am close and this is good enough for non-critical work because paper is fairly consistent at two or three thou in thickness.

[AccuMillGuy]

Thank you Geof.

I do not have a edge finder at the moment (did not know they existed) what can I use untill I get one (ASAP)?

Thanks

Originally Posted by Geof You need to use the same reference point in the machine as you use for the drawing; in your case the top left front corner. This means you have to find the X and Y coordinates for this corner and enter them into the G54 work offset table. One way to get the coordinates is use an edge finder on the sides of the piece; your Trainer should be able to show how to use an edge finder. The tool offset is set to the top of the part. There are various ways to do this but the most direct is to bring the tool down to the part. I use paper between the tool and part to find out when I am close and this is good enough for non-critical work because paper is fairly consistent at two or three thou in thickness.

[Geof]

Originally Posted by AccuMillGuy Thank you Geof. I do not have a edge finder at the moment (did not know they existed) what can I use untill I get one (ASAP)? Thanks

Put a piece of round stock in a toolholder and use this to detect the edge of your work again with a piece of paper between. Go carefully in jog mog of course set at 0.001" per click. You will feel the paper get gently gripped and if you go one more thou it will probably tear instead of pulling out of the gap.

Now raise above the work piece and move further in the radius of your round stock and the spindle centerline is on the edge of the stock.

You can enhance your accuracy by rotating the tool holder by hand when it has barely touched the paper and see if the paper gets tighter at a particular position of the spindle suggesting that your round stock is running out. Then you do the operation at the tight spot and the spot 180 degrees opposite and take the average.

[AccuMillGuy]

Thank you. I do not know why I did not think of this... LOL

I will do that on both X and Y side of the work peace, subtract the radius from those figures and that will be my work peace point 0.

Thanks for wakening my dead brain cells ;-)

Adam

Originally Posted by Geof Put a piece of round stock in a toolholder and use this to detect the edge of your work again with a piece of paper between. Go carefully in jog mog of course set at 0.001" per click. You will feel the paper get gently gripped and if you go one more thou it will probably tear instead of pulling out of the gap. Now raise above the work piece and move further in the radius of your round stock and the spindle centerline is on the edge of the stock. You can enhance your accuracy by rotating the tool holder by hand when it has barely touched the paper and see if the paper gets tighter at a particular position of the spindle suggesting that your round stock is running out. Then you do the operation at the tight spot and the spot 180 degrees opposite and take the average.

[Geof]

Originally Posted by AccuMillGuy Thank you. I do not know why I did not think of this... LOL....Adam

Because you probably fell into the trap I did when I first started with CNC; always trying think of the complicated way to do things. Then I realised these machines are not magic and I don't have to work to within a kazillionth of an inch all the time.

When that is needed I take out my high quality paper.

[masonbcaldwell4]

Originally Posted by Geof Put a piece of round stock in a toolholder and use this to detect the edge of your work again with a piece of paper between. Go carefully in jog mog of course set at 0.001" per click. You will feel the paper get gently gripped and if you go one more thou it will probably tear instead of pulling out of the gap.

you can do pretty much the same thing with the tool in the spindle and the spindle running, just use a long strip of paper to keep your hands clear of the cutter, bring it in slowly until the cutter Starts to tug the paper out of your hand... just a different technique.

[A_M_Roth]

I'm not sure if this is considered shoddy practice or not, but I do the same as the other posters except I use .010" of shim stock that is kept handy, near the door on a magnet. Then just do the math to set "Z". Also, if the surface is to be face milled, I'll "scratch" the material with the spindle turning, back off the one or two thousandths and set "Z". Again, I'm not sure if these techniques that I use are considered "proper", but it works too.
For "X" and "Y", I'll come in .010-.020" from each so that I get clean machined work, to keep saw marks and such from scrapping an otherwise good part.

[Geof]

Originally Posted by A_M_Roth ....Also, if the surface is to be face milled, I'll "scratch" the material with the spindle turning, back off the one or two thousandths and set "Z". Again, I'm not sure if these techniques that I use are considered "proper", but it works too....

Why worry if it is safe and it works.

Here is a refinement on your 'scratch' technique that can be used on good surfaces. Get a nice fat felt tip pen and draw a spot larger than your cutter size. Bring your cutter down with the spindle turning in jog mode set at 0.0001" per increment of the jogwheel; stop when you see the cutter shaving off the ink.

[A_M_Roth]

I've seen that done too, now that you bring it up.