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Author Topic: Soft Limits Stop Short  (Read 3065 times)

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Soft Limits Stop Short
« on: July 17, 2007, 10:11:44 PM »
I moved my Z axis the other day plunging a bit too vigorously.  I reset it today and in the process checked to make sure the soft limits stopped where they should.  They stop exactly .100 inch short both up and down.  I went on to check the X and Y and they are doing the exact same thing.  I have no idea when this behavior started.

Can someone tell me what's going on?

Thanks,
Walt
Re: Soft Limits Stop Short
« Reply #1 on: July 18, 2007, 09:34:59 AM »
Sporty, this behavior started of course when soft limits were turned on ! Look in the homing,limits setup page and you will see soft limits min and max ! If you set them all up the way they need to be for your machine they are a very good thing and will prevent overtravel and going through a limit. Just be sure to turn it off to re home machine, and turn it back on after you home and drive off of home enough to clear soft limits. Also, i found the best way to set the max limit is to run machine into the oposite limits, then write this value minus a safe value into the setup, also you can set home "z" value by by clearing z work piece offset and zeroing the face of the spindle to the table with feeler gauge and leave a few thou clearance, turn off auto zero, and re referance the z axis and write this value into setup and re turn on auto zero, so that when you home referance z this value is automatically put into the dro and the face of spindle (no tool or holder !) is now a known distance from table top. When it is all set up properly it is ever so nice to use, just measure tool, measure wpo, and you know your there ! Play with it till you know it well, and use the slow zone setting too so that when you drive to the limit it will slow down and creep up to the set stop point ! Keep in mind that the z setting at the table will be needing either setting for the job, each and every time you change or a value which will be ignored in the job. I set it to face of spindle to table value so it is ignore in job so it is still possible to drive a tool into table, but it won't fault you out in program and cutting part.
CRUISER
  Don
Re: Soft Limits Stop Short
« Reply #2 on: July 18, 2007, 10:41:12 AM »
Cruiser,

You're misunderstanding the problem.  I've always used soft limits.  They have always been turned on.  It's just that now, they are stopping short of where they are set to stop.

For example:  The Z+ is set to stop at 1.500.  It actually stops at 1.400.  All the axis do this.  I have no idea when it started because I can't remember the last time I actually ran right up against a stop.  Even if I had, I don't have the values memorized so I wouldn't have noticed.

There must be a .100 value somewhere that is figuring into the equation but I sure don't see it.

Thanks again,
Walt

Offline jimpinder

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Re: Soft Limits Stop Short
« Reply #3 on: July 18, 2007, 02:05:07 PM »
This is just a shot in the dark, because I don't really know what I am talking about, but it helps my understanding, if not yours !!!

If it is happening on all the axis, it would seem that Mach 3 is making some sort of adjustment, and it would appear to me that a tool diameter or something similar is being allowed for, or some other safe offset is being introduced.


Not me driving the engine - I'm better looking.
Re: Soft Limits Stop Short
« Reply #4 on: July 18, 2007, 10:34:43 PM »
Hi Jim,

I'm sure you must be right, but just what adjustment it's making is the mystery.  I installed 2.02 just to be sure it wasn't the version I was using.  It didn't help.

In fact, the problem seems to be a bit random.  The axis are not all .100 off now, they are all different and inconsistent.  The only consistency is that they get close to the designated value but don't actually hit it which means they also never hit the limit switches.

I've decided it's like sausage.  It works so don't look at it too closely.

Thanks again,
Walt

Offline jimpinder

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Re: Soft Limits Stop Short
« Reply #5 on: July 19, 2007, 04:26:30 AM »
Walt -

I think what I would do in the circumstances is use a packing in front of the switch say the 0.1 (or anything really that you can measure with a digital caliper) that the table is stopping short, then move the software limit in by the same amount. See if the fault repeats itself.

If it does it is a software fault, if it doesn't it might be a mecanical fault.  At the ends of my traverses, I have "sticky" bits that are not used a lot, and the steppers sometimes miss a few steps.  It is not too important at the moment, because I am trying to find out the limits of travel, so I'm watching for it, but it will bother me  when I want to set it up properly.


Jim
Not me driving the engine - I'm better looking.
Re: Soft Limits Stop Short
« Reply #6 on: July 19, 2007, 01:37:16 PM »
Well the problem, if you can call something so trivial a problem, disappeared as mysteriously as it appeared.  Today, everything is once again working flawlessly.

Regards,
Walt