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Author Topic: End limit switches and homing switches (Mach3, G540, CNC converted X2 mill)  (Read 14662 times)

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Hi.

I am working on my Mach3 + G540 + X2 CNC project. I have basic motion now it looks like, but I need to mount limit switches before I risk testing the machine more than some small basic moves with my have on the E-stop button. No spindle operation yet. I wont want to damage the motor couplings or the ball-screws!

This is my first CNC project so I have some questions:

Do I actually need end limit switches? My steppers is specified to give 381 OZ-IN torque (approx 30 kg on 1cm arm). Some people write that they do not need end limits switches if they do not use servos. I am skeptical to this. What is your opinion?

Should the homing switches trigger "in the middle" of the axis travel? Do I need an extra homing switch in the middle, or can the homing switch double as an end limit switch?




What coordinate system is used in the "CNC world"? Is it a right handed coordinate system?

Is the below correct?
X axis: Left to right. Maximum left is zero X, maximum right is maximum positive X coordinate?
Y axis: Front to back. Maximum towards the operator is zero Y, maximum towards the column is maximum positive Y coordinate?
Z axis: Bottom to top. Lowest position towards the table is zero Z, maximum height is maximum positive Z coordinate.




I have watched the videos for the Mach 3 software. Where do I find more detailed documentation on how to set up and practical use the software? I want to remove some material from an alu block, mill some holes in an alu plate etc. Mostly very basic operations. (I am a beginner when it comes to NC code, CNC, Mach3 but i have extensive electronics background).

Offline Hood

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First the coords, your X and Y are correct as long as you are talking about the tool in X, ie table fully right means tool is over left corner.
Same with Y but you mention the table there so you may be thinking wrong, table fully back to column is Y 0.
Z fully up is 0 and from there down is a negative value.

Regarding limits/homes, you can share all switches and use just one input. When homing Mach will see the switch as a home switch, all other times it will see it as a limit.
 Having seperate home switches can be a good thing in some situations, some controllers can allow Index homing if you have servos. The machine will home, hit the switch then look for the index pulse from the encoder and set that as machine zero. Also if you have a big machine with long travels it may be an advantage to have a home switch further in from end of travel but for your size machine that is not a benefit really.

Hood
« Last Edit: January 06, 2013, 05:24:18 AM by Hood »
I was talking about the table. I may have it all wrong then.

Should I always refer to the tool bit tip position on the workpiece when I specify coordinates? Not the position on of the table?

On the ballscrew kit that I purchased from CNCFusion there are minus and plus signs milled into the motor and bearing holders. Plus is to the right and minus is on the left for the X axis. Minus are towards me and plus are towards the column. Confusing!

See attached photo (click to enlarge). Here you can see the markings that are milled into the kit from CNCfusion. Does this mean that the leftern part of the workpiece and the part of the workpiece that is closest to the belly of the operator are the maximum positive coordinates (of the tip of the tool compared to zero of the workpiece?

The zero is then righternmost part of the workpiece most far away from the belly of the operator?

Max Z is then the deepest cut?
« Last Edit: January 06, 2013, 06:27:41 AM by Mike1000 »

Offline Hood

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Table fully right means tool fully left in relation to work and that is X0 (Machine Coords)
Table fully towards column means tool fully towards you in relation to work piece so that is Y0
Head fully up is tool fully up and that is Z Zero.

So what you have in pic is X0 Y0 Z 0

Markings on covers are correct for X if it is meaning table direction but that means wrong for Y and vice versa. Think of a graph on a piece of paper, lower left is X0Y0. If you look down on your mill from above that is like the graph, so tool over lower left corner is X0Y0 which means table fully right and fully towards column.

Hood
OK I think I get it. The markings on the CNC fusion kit must mean that when the tip of the TOOL moves right on the Z axis, the coordinates increase. When the tip of the TOOL moves towards the column, the Y increases.

Z increases when the cut is taken.

Thanks!

Offline Hood

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The markings are wrong, depends whether they are referring to travel of table or tool..
When table moves right the tool is moving negative in relation to your work and vice versa.
When table is moving away from you the tool is moving negative in relation to work.
When Z is moving up Tool is moving positive but as fully positive on Z is zero then fully up is zero and all down moves are negative numbers.

Always think of the tool in relation to the work rather than axis direction. It is a bit confusing and these markings are not helping as they are wrong, or at least one is wrong and one right depending on what they represent (table or tool direction)
Hood

Offline Hood

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Just to clarify, where your tool is in the pic is X0Y0Z0 in machine coords.
Hood
OK I think I get it.

The green "dot/blob" is X0 and Y0.
If the tool moves right the Z is increasing.
If the tool moves towards the column, the Y is increasing.

I think BOTH markings (milled markings in the alu) are wrong, not only one of them. Do you concur?

Correction !!!

The green "dot/blob" is X0 and Y0.
If the tool moves right the *X* (not Z) is increasing.
If the tool moves towards the column, the Y is increasing.

I think BOTH markings (milled markings in the alu) are wrong, not only one of them. Do you concur?

Offline Hood

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Yes green blob would represent X Y Z 0 for your machine coords and moving in the directions you state is correct.


Regarding the markings on the table, sorry for the confusion, I  have just zoomed in on the pic and the X is the opposite to what I thought it was. The markings for both X and Y are correct if you are thinking they represent the tool in relation to the work but they are wrong if they are meant to represent the table movement.
Hood