Need help setting my soft-limits

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h00die
Posts: 2
Joined: Thu May 05, 2022 9:35 am

Need help setting my soft-limits

Post by h00die » Mon May 16, 2022 3:41 pm

Hey all - just finished my wiring and am doing the setup on a 3-axis mini-mill. I need some help setting my soft-limits correctly.

I have proxy switches on what would be the X-max, Y-max, and Z-max ends of the feeds - and have set each of the motors to switch-max for homing.

My settings are:

Motor 0 (X) - min-soft limit: 0, max-soft-limit: 250, latch-backoff: 5
Motor 1 (Y) - min-soft limit: 0, max-soft-limit: 150, latch-backoff: 5
Motor 2 (Z) - min-soft limit: 75**, max-soft-limit: 250, latch-backoff: 5

The homing procedure there works fine, and backs off as it's supposed to 5mm and sets my position to 250/150/250 (so zero is over at the min-end of the feeds, which makes sense). So the machine should understand the extent of it's working envelope.

(**on my Z, I don't want the spindle to get less than 75mm above my table given the stick-out of the collet, tool, fixtures, etc)

Now I want to zero on my workpiece. So I jog the table, touch off the top-center of my workpiece, and zero it there...because that's how I roll.

With my WCS also set at top-center of the stock, this means that all my cuts are -Z, and EITHER +/- X, or +/-Y from *zero*. When I attempt to run my program, however, it dies saying I can't move the tool (z) below 0. Which I guess makes sense given my settings. I'm going to guess, too, it would complain about -X and -Y movements too in that case.

So I'm confused as to expressing the limits of machine travel on the feeds, versus establishing zero on the workpiece for purposes of running my gcode...are soft-limits based on Zero? Or are soft-limits based on home? It seems like they're based off zero, which wouldn't make sense.

What am I missing? (ans: likely, all of it)

Thx for listening

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Doug
Posts: 343
Joined: Fri Feb 02, 2018 4:56 pm

Re: Need help setting my soft-limits

Post by Doug » Mon May 16, 2022 6:31 pm

Soft limits are the absolute limits found during homing.

Let's say that the center of your work piece is exactly in the center of your machine and that is where you zero your offsets. This would be x=125 and y = 75. During a cut, your x axis should be able to move anywhere from -125 to +125 and y should be able to move anywhere from -75 to +75 without causing an error.

Z is a little more tricky. In order for z to work correctly, the top surface of your work piece must be more than 75mm above the surface of the table. Lets say the surface of your work piece is 100mm above the table and that is where you zero it. If the program would cause the z-axis to move below -25mm, it would go below your min soft limit and cause an error.

For me, it would be simpler to set the surface of your table to be -75 and the top of your z axis to be 175. That way, the z-axis would usually be somewhere in the mid range and far away from the soft limits.

h00die
Posts: 2
Joined: Thu May 05, 2022 9:35 am

Re: Need help setting my soft-limits

Post by h00die » Tue May 17, 2022 7:50 am

OK - I'll try these and see how they do.

I'm still not sure I understand tho as this seems to indicate that soft-limits are relative to the workpiece (were zero is set) not relative to the machine as determined by home. Which means that the soft limits may need to be changed from piece to piece depending (large piece vs small, zero at center or at edge).

I'll try it this way, see how it works - maybe I need to just see things in motion to fully understand the relationships.

TimATX
Posts: 2
Joined: Tue Apr 14, 2020 6:00 pm

Re: Need help setting my soft-limits

Post by TimATX » Thu Jul 14, 2022 9:15 am

So, are offsets required to be changed for each job? I'm trying to set my controller up right now and the soft limits are causing grief.

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Doug
Posts: 343
Joined: Fri Feb 02, 2018 4:56 pm

Re: Need help setting my soft-limits

Post by Doug » Sun Jul 17, 2022 2:41 pm

Offsets are used to tell the controller where the work piece is located. You should place the work piece on the table, jog the bit into the x=0, y=0, z=0 position and then click the zero offsets button to tell the controller that is position (0,0,0).

If you move the work piece, you will have to change the offsets.

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