[Mr.Chips]

I have built a Fixed Gantry CNC and am unsure as to which direction should be “X”. I see it shown in both directions in this forum. Should “X” be parallel to the Gantry or perpendicular?

I have drawn a top view of my CNC and have me standing at the lower right side. The Fixed Gantry is naturally offset to the upper side of the machine. So I want to load the movable table and position material for cutting in the lower half. And I want the Zero Zero home of the router to be as indicated for ease of bit change and measuring offsets when positioning material.

Thanks

Hager

[HuFlungDung]

Its probably optional, but the only criteria I can think of would be to make the X axis the longest axis, only for the sake of doing CADCAM later on, when your widescreen computer screen makes it handy to work that way. At least the few cad programs I have used have always used the horizontal axis as the X and if there is a cursor position readout somewhere, it will also follow that convention.

[Mr.Chips]

Its probably optional, but the only criteria I can think of would be to make the X axis the longest axis, only for the sake of doing CADCAM later on, when your widescreen computer screen makes it handy to work that way. At least the few cad programs I have used have always used the horizontal axis as the X and if there is a cursor position readout somewhere, it will also follow that convention.

That sounds like a good choice as the Table is longer in the perpendicular direction to the Gantry, as shown in Red lettering.
And I think it would not be upside down in reference to where I am standing, Right?

[ger21]

If the gantry is Y, you'll want the 0,0 position to your left, or the lower right corner of the drawing. You want the table to match your CAD orientation, so what you draw on the screen matches what your machine is cutting. Usually, X+ is to the right, and Y+ is up.

Typically, the longer axis is X, as Hu siad, but you can set it up any way you want. Just set it up the best way to match your design software.

[HuFlungDung]

There should not be any restriction that way. Your machine zero typically can be defined to be whatever and wherever you like. That is to say, when the machine hits the homing switches, you can call that zero, or define (in parameters) a different position.

You do want to keep with convention that defines the direction left of zero as X-, and towards you as Y-.

[ger21]

Yeah, the 0,0 can be anywhere. But the way he had it, the directions were backwards. His Y axis was correct, but the X axis was backwards.

[Mr.Chips]

Let me try this again.
The drawis how I want letters to be cut.

And the "C" corner is where I would like the router to be when changing bits. But this man not turn out to be the Zero Zero position, in which case I will have to address that.

The lettering direction is the "X" direction.

SO, where would Zero Zero be?

Remember this is a movable table and not movable gantry, I think that makes a difference in + movement, at least that is where I'm confused.

[ger21]

Remember this is a movable table and not movable gantry, I think that makes a difference in + movement, at least that is where I'm confused.

No, it doesn't, it just appears to. Keep in mind that what you want to know is which way the tool moves, not which way the table moves.

Again, 0,0 can be wherever you want. You want the tables coordinate orientation to match the coordinate orientation in your CAD or design program. Typically, X+ is to the right, Y+ is to the left. So, like I said before, normally 0,0 would be the lower left corner of the design, or the lower right on your drawing. Keep in mind that it's possible to design your text so that all the coordinates have negative values. In this case, you'd need to move the origin to the other end of the table, but the axis directions would remain the same. That's what Hu was talking about. unless you mount your parts in the same place every time, your part origin an change with each part, usually referenced off the lower left corner of the part.

Now going back to which way the tool moves. If the origin is at the bottom of your pic, X+ is towards the gantry. But as the table moves towards the gantry, you're actually traveling in the X- direction.


Make sense?

[ger21]

I did a little sketch. The X+ and Y+ direction will always remain the same, but the 0,0 point can move anywhere on the table that you place your part. Just remember that in this example, the part is designed with the 0,0 point at the lower left.


It's confusing, but it is possible to have the 0,0 point be anywhere on the part.

[Mr.Chips]

I did a little sketch. The X+ and Y+ direction will always remain the same, but the 0,0 point can move anywhere on the table that you place your part. Just remember that in this example, the part is designed with the 0,0 point at the lower left.


It's confusing, but it is possible to have the 0,0 point be anywhere on the part.

Yes it is confusing, and sketches help.
I may be confusing Origin and 0,0?

I define 0,0 to be in the lower right corner of the table as in your example.

If write text to be cut at X +1 and Y +1 (D) then the text would come out in the X axis and starting in the lower right corner of the table (D). To do this the table would drive to the upper end of the of it's travle and then start cutting. Is this correct?

[ger21]

Yes it is confusing, and sketches help.
I may be confusing Origin and 0,0?

I define 0,0 to be in the lower right corner of the table as in your example.

If write text to be cut at X +1 and Y +1 (D) then the text would come out in the X axis and starting in the lower right corner of the table (D). To do this the table would drive to the upper end of the of it's travel and then start cutting. Is this correct?

I'm using origin and 0,0 to be the same thing. Sorry for adding confusion.

Yes, I think you have it.

[Mr.Chips]

I think I have it now. But please take one more look.

Start off by homing the machine, that's 0,0, as shown in the "Start Cutting drawing". This is also the Origin, Correct?

Then I would load the part to be cut by manually driving the table to X+23 and Y0, as shown in the "Load Part" drawing.

Then press START.
The table would drive to 0,0 and start cutting. As shown in the "Start Cutting drawing".

[ger21]

I think I have it now. But please take one more look.

Start off by homing the machine, that's 0,0, as shown in the "Start Cutting drawing". This is also the Origin, Correct?

Yes, provided you have some type of stop or fence or other system setup to reference your part to your "home" location.

Then I would load the part to be cut by manually driving the table to X+23 and Y0, as shown in the "Load Part" drawing.

Then press START.
The table would drive to 0,0 and start cutting. As shown in the "Start Cutting drawing".

Basically, yes. It won't necessarily go to 0,0 first, it will just go where the g-code tells it to.


If it were my machine, I'd do it a bit different. I'd make the home position X23, Y0. Then, when you home the machine, it's out of the way. If using Mach3, you can set a home offset of X 23 so that when you home the machine it will set the X to 23. This way you won't always have to move the table to load and unload your parts.

[HuFlungDung]

Mr Chips,

Ger is doing a good job of explaining, but I'll add one more point of fact: at the machine setup stage, all you have to worry about is setting up your motors so that jogging in X+ moves your tool to the right end of the work. Whether the table moves or the spindle moves may in fact require a reversal of motor direction to accomplish. However, motor reversal is usually fairly easy to do, should you happen to get it backwards at some point in setting up your first part to cut.

What you don't have to worry about is where your zero is, assuming that you will have it at one extreme corner of the table. This is because your work coordinate system rides piggyback on top of the machine's coordinate system, which is called G53. Normally, we would never, except by a freak accident, have the part zero correspond to the machine zero, for many reasons.

For example, if you needed to contour around the perimeter of a square near the maximum capacity of your machine, and you set the work up with two sides set right on the edge of the machine zero, then you could not actually get the tool out past the edge. So you'd have to move the work over enough to fit the tool in between the extreme edges of travel and your part.

At the same time, it would be most inconvenient to reprogram the toolpaths because you moved the part over, and it is totally unnecessary to do so.

So, a work shift, commonly using G54, is the first step toward learning about shifting an imaginary coordinate system's origin relative to an underlying G53 coordinate system which your machine uses to understand its own physical travel limits.

So in the example of machining around the perimeter of a square, using a 1" diameter tool, you would perhaps want to shift the work away from the fence by 1" so you'd slap a one inch spacer on the table fences and then clamp down the part. If the machine zero (G53 X0Y0 was 1" away on a diagonal, then you can shift the work's origin by inserting appropriate values into the G54 register: X1 and Y1 would be the values (I disregarded sign, but a little trial and error would clear that up).

No matter what, if you get the axis directions moving in the conventional directions, you can worry about the machine zero later. Its of no consequence where it is, you'll never be 'stuck' because you set the machine up with homed zero in a certain place.

Edit: BTW, it is important to follow the axis direction conventions in order to keep your arc commands 'conventional' as well, otherwise you'll probably have to muck around with your post processor and you'll become mentally maimed for life

[joecnc2006]

The way I look at it is how it is in Cadd, Y is up and down, and X-is left to right, so depending on which side will be your front. On my CNC Model 2006, the side is actually the front so the bed is X-Axis., on my new 4x4 the front is actually the front so my moving gantry is the X-Axis and the bed left to right between the rails are Y-Axis.

Joe

[Mr.Chips]

Thank you all.
I think I will take this and try it out on some text that is positioned away from the extremes of travle.

Hager

[Mr.Chips]

Went into Mach 3 and changed the input pin ports, switching X to the long axis.

Ran the Engraving wizard and typed some text. It came out just fine and parallel to the X axis as expected.

I then had a DXF file that my friend had created ion Turbo Cad. When I ran it, it wanted to cut the piece with the base on the "X" axis abd the part is 20" tall. I had to switch the input pin ports back , switching Y to the long axis. This file was cutting where it should not have, and O posted that in another link.

Hmmmm
How could you change the cut orientation without switching the input pins? This was a mickey mouse way to do it.

[ger21]

Hmmmm
How could you change the cut orientation without switching the input pins? This was a mickey mouse way to do it.

Rotate it in a CAD program. I was going to do that for you when I fixed the .dxf, but wasn't sure what you were doing with it. I believe there is a g-code to rotate it in Mach3, but have never used it. Maybe G68?