Help cutting Arcs in Mach 3

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Dave_C
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Help cutting Arcs in Mach 3

Post by Dave_C »

Help!!!
For some reason I can not get it in my head how to program arcs in Mach 3 for my Lathe using a front tool Post.

I have the "Reverse arcs in front tool post" checked in the setup under port and pins. I can run the wizards that cut arcs and they work just fine but when I try to modify them, they don't work.

For example: Lets say we have a 3" od Stock in the chuck. And we want to cut an arc that makes a semi circle on the end (ball end).

I can see from the code that it uses I and K but I can't understand the logic for some reason..

I know the arcs start from the current tool position. So if i am at z-1.5 and I want to cut a radius of 1.5" to make a ball end the code looks like this:


G03 X0 Z0 I-1.5 K-0

Normally the X and X positions written are the "go to" locations, so I guess this is going to the end and the center. The K must be the offset from center for the arc end?

Is there a better way to learn this that can be explained in logical terms so I can write this myself?

Dave C.
I learn something new every day! Problem is I forget two.
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GlennW
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Re: Help cutting Arcs in Mach 3

Post by GlennW »

"I" and "K" represent the center point of the arc.

"I" represents the "X" axis pivot point and "K" represents the "Z" axis pivot point
Glenn

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Dave_C
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Re: Help cutting Arcs in Mach 3

Post by Dave_C »

Glenn,

Ok, that is what I am looking for!

So when we past the 90 degrees part of the arc the center point reference must change from I to K or vice versa.

Does Mach 3 let you use the R input and then just define an endpoint? (Instead of the I and K values)

Dave C.
I learn something new every day! Problem is I forget two.
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GlennW
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Re: Help cutting Arcs in Mach 3

Post by GlennW »

The center point needs to be referenced by both "I" and "K". They would remain the same through 360 degrees of arc.

I've never even seen Mach3, so I won't be of much help there.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
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Dave_C
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Re: Help cutting Arcs in Mach 3

Post by Dave_C »

Glenn,

Ok, I think I got it! I and K are like X and Z as far as defining a point in the coordinate system.

So from the cutter current position I need to define the center of the arc and "I" would be the X coordinate number and "K" is the Z coordinate number making a "Pivot Point" from where I am at. Then the other part of the line is the end of the arc coordinates.

I might just be able to learn this (With a little more help)

Thanks,

Dave C.
I learn something new every day! Problem is I forget two.
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GlennW
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Re: Help cutting Arcs in Mach 3

Post by GlennW »

Looks like you've got it!

Really GREAT job on the conversion. Looks like fun!
Glenn

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Dave_C
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Re: Help cutting Arcs in Mach 3

Post by Dave_C »

Glen,

I just wanted to add to our discussion about "I" and "K" in CNC Lathe work. The simple explanation you gave me was what I needed but I still had trouble figuring out why "I" was always a negative number and then I remembered that Mach3 ARCs use "Incremental" positions and not Part Coordinate positions.

So I played with the math a bit writing some progressive arc cuts. It became obvious that my "I" stayed put while the "K moved because as I started with small cuts the "K" had to be a larger negative number to keep the pivot point of the arc in the same place.

So I came up with a formula based on my 3" OD stock cutting a ball on the end:

If I = 1.5" then K = 1.5 - the current Z position.

So if I make my first small pass .0434" back from the end of the part, then K has to be a negative number to keep the arc pivot at 1.5" from the end. So subtract .0434 from 1.5" and you get your K number of -1.4573.

It works for as many steps as you want till you get to the end and then K is 0 as you have the tool directly over the pivot on the Z axis and since you are 1.5" away from the center line, you still have an incremental value for "I" of -1.5.

Last line looks like this: G03 X0 Z0 I-1.5 K-0

Thanks for the help,

Dave C.
I learn something new every day! Problem is I forget two.
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