Author Topic: Soft Limits  (Read 6269 times)

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Offline Hood

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Re: Soft Limits
« Reply #10 on: November 24, 2008, 06:16:54 PM »
Regarding the Z axis, you are getting confused between machine coords and work offsets. Machine coords has the Z zero as furthest from the table and all movement is negative. However just like for X and Y when you jog down to your work you can set a Work offset zero at the surface and above will be positive and below negative, machine coords will still be all negative though and you can confirm by looking at them.

Your X and Y are correct for home position, well I say correct as in industry it tends to be the opposite for the Y but they use a Home Off value so when they home the machine knows it is + full travel. You could do the same in Mach but if you are happy with your homes that way then you dont need to :)

Hood



Offline Hood

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Re: Soft Limits
« Reply #11 on: November 24, 2008, 06:19:46 PM »
Oh wait a min are you meaning the cutter or the table is nearest you? My pic is actually wrong in a way as the dot is showing the correct position for the X and Y zero but I should have had the table in to the column.
Hood
« Last Edit: November 24, 2008, 06:23:02 PM by Hood »

Offline HimyKabibble

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Re: Soft Limits
« Reply #12 on: November 24, 2008, 07:04:07 PM »
Okay, I'm back after a computer meltdown. If it isn't one thing it's another....
I have reread all the posts re: this subject several times now, and I still need some clarity. Firstly, unless I have completely misunderstood some of the posts, it seems that there is some disagreement about the Z axis and whether it is standard for the Z zero to be set at the high part of its range, and everything below that (closer to the table) is negative. Others seem to think that Z zero should be set at the work surface, and everything above that should be positive. In the case of the Z zero at the top, a soft limit above the Z zero position would be positive, but it would be negative if it is set below the low position. In the latter case (the Z zero is at the work surface), the soft limit would have to be negative if it is below the work surface. The problem as I see it with the first configuration is that you have to work with negatives, measuring down from your tool bit and then adding another negative number to that to get the cut depth you want. The problem with the second method is that if you want your tool to go home after doing a procedure, or to get ready for another procedure, it would travel at the height of, and/or end up at, the work surface, making it hard to remove the work and possibly damaging the surface of the material.
So, let's solve that first.
As to Hood's question about my machine orientation, the lower left corner of the XY axes is near the operator and on his left. As of yet, there are no limit or home switches -- this is why I want to get this soft limit thing correct.
Is it possible to avoid some of the issues mentioned above by having the soft limits be the home and positions away from home beyond which you don't want to go (that is, what I would consider the usable work surface), and the slow down 1/4 inch, say, before that? The only problem that I can see is that the machine slows down when it is working near the limits...is that a problem?
Thanks again, Bob

I think your mixing home positions, machine coordinates, and work coordinates all together.  The home position can be where you want it to be.  It is probably most often set to one corner of the X/Y travel, and, I think, *always* full up on Z.  Work coordinates are generally zeroed somewhere else that is on, or at least relative to, the actual workpiece.  It is conventional for Z=0 in work coordinates to be the top-most surface of the workpiece.  Moving Z in the minus direction always moves the tool downward.  If you have no home switches, then machine coordinates have relatively little meaning, and you can define machine zero to be wherever you like on a job-by-job basis, and set work coordinates to be the same.

Regards,
Ray L.
Regards,
Ray L.

Offline rabphxaz

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Re: Soft Limits
« Reply #13 on: November 24, 2008, 09:03:16 PM »
Well, that helps. If I forget about home positions and work coordinates, and concentrate solely on machine coordinates in order to set my soft limits, then could I dial them in kind of like what I talked about in the previous post, that is, the soft limits and the max and min machine coordinates are the same, with a 1/4 inch slow down in front of them?
Thanks again, Bob

Offline Hood

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Re: Soft Limits
« Reply #14 on: November 25, 2008, 05:08:25 AM »
Bob
 If you dont have home switches then you can still use the softlimits but for them to be of any use you will need to simulate a homing operation. What you can do is have marks on each axis at their extremes and move to them by jogging. Once you are there then you can press Ref All button and if you are looking at machine coords you should see all DROs go to zero, that is you now homed. You can now set up softlimits and slow zones as required.
 It is important to know where your tool is in relation to your home position as that will determine whether you need to set a Home Off value for any of your axis. If your Axis did not zero in Machine Cords when you pressed the Ref All button then firstly make sure you are indeed looking at the machine coords by checking the machine coords button has been pressed and is active. If that still doesnt show the DROs being zero then go to Config menu then Homing and Limits and check the Auto Zero is chosen for each axis.
 Once you are fine with all that then you are all set and you can enable the SoftLimits via the button on the main page in Mach.
Hood

Offline rabphxaz

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Re: Soft Limits
« Reply #15 on: November 25, 2008, 08:00:47 AM »
OK, thanks, I'll work with this and see what happens. Hood, I see that you're from Scotland, you ever read any George MacDonald Fraser, my favorite author?
Bob

Offline Hood

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Re: Soft Limits
« Reply #16 on: November 25, 2008, 08:04:32 AM »
afraid not, cant read ;D
 

Hood

Offline rabphxaz

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Re: Soft Limits
« Reply #17 on: November 25, 2008, 08:31:00 AM »
Well, if you ever decide to learn, give Fraser a try -- his Flashman series is the funniest stuff I've ever read.
Thanks again, Bob