Author Topic: Setting up my home machine coordinate position, without homing or limit switches  (Read 7840 times)

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Offline DavePr

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I need some help from the experts. I have a home built machine that I purchased. It is about 5' x 12'. I have the bed set up to cut out 49" x 97". I want to set my home position in the lower right corner if you were looking at the machine from the front. I know that I can move the machine to that point and either zero all the DRO's and it will return there each time I push the move to zero buttton. Until, I turn the computer off. Then it goes to another spot. I have tried putting the machine in the spot I want and then clicking the Ref All button, but it doesn't seem to work. Also, the guy I bought it from and a very small section of the overall table set up in the soft limits. I have scoured the forums on here and CNCzone to see if I could find the answer, but it seems like all the ideas are discussed around having switches hooked up. Some days I'm sure I will get to that point, but it wont be for a while. So if anyone can help me, I would sure appreciate it.

Thanks
Dave

Offline Hal

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Try the "ZERO X" and "ZERO Y" buttons beside the DRO line.

For safety it is best to have the limit switches installed. You never know when a mistake will make you wish you had. The Home switches are nice for running repeat parts.

The soft limits could be used to limit the travel. If your work area was 12 x 12. You could set the limits to clear your stock and cutter. This should limit the travel to just your working area.

The normal practice is to use normally closed switches and wiring. If you break a wire the machine will stop. I run a Gecko 540 and there are connections for the home and limit switches. Check your breakout board for inputs for the switches. Mach3 will have port and pin settings for the inputs.

Hal

Offline BR549

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MANY stepper machines are set up without homes or limits.  Most set up  hard stops on xyz to bump up against then set ref home. IF you have no switches setup then when you press refhome it sets the machine HOME to the exact spot you are at. simply move to the stops bump up against it and refhome. Once you have refhome then the softlimits can be made active and that will allow you a saftey when running a program just make the Softlimits to be just inside the max travels of the machine.

Bumping the machine up against the stops with a stepper drive causes no harm or foul to the drives or motors.

IF you look at the gen config you will find a check box to make the DRO positions persistant or be the same as when you shut down mach3 when you restart mach3.

Just a thought, (;-)TP


Offline HimyKabibble

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MANY stepper machines are set up without homes or limits.  Most set up  hard stops on xyz to bump up against then set ref home. IF you have no switches setup then when you press refhome it sets the machine HOME to the exact spot you are at. simply move to the stops bump up against it and refhome. Once you have refhome then the softlimits can be made active and that will allow you a saftey when running a program just make the Softlimits to be just inside the max travels of the machine.

Bumping the machine up against the stops with a stepper drive causes no harm or foul to the drives or motors.

IF you look at the gen config you will find a check box to make the DRO positions persistant or be the same as when you shut down mach3 when you restart mach3.

Just a thought, (;-)TP



Terry,

That makes no sense to me....  When you run a stepper into a hard stop, the motor will actually stop at one of four full-step positions (assuming a typical 2-phase stepper), but the controller will almost certainly believe the motor to be at a different position that is some unknown number of steps beyond the physical position.  Micro-stepping further clouds things.

Regards,
Ray L.
Regards,
Ray L.

Offline Hood

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Ray, would it matter where the motor stopped? If it is stopping on a full step then all the better. Mach zeroes the machine coords when you Home so what the rotational position of the motor is, is irrelevant as far as I can see.
Maybe I am missing something?
Hood

Offline HimyKabibble

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Ray, would it matter where the motor stopped? If it is stopping on a full step then all the better. Mach zeroes the machine coords when you Home so what the rotational position of the motor is, is irrelevant as far as I can see.
Maybe I am missing something?
Hood

Hood,

Yes, you're missing something.  With no micro-stepping, the driver has a sequence of four output phases it cycles through.  When you hit the hard stop, the motor may stop on phase 1, but the controller may stop on phase 3, since it can't sense where the motor actually stopped.  The first step the driver makes may not move the motor at all, or may even try to move it in the wrong direction.  The result is, you will end up with an error of up to several steps before the motor catches up to where the controller thinks it is.  This is basically the same problem you have with stopping the machine at a specific position, then powering down, and powering up the controller.  The controller will generally power up in one specific phase, and the motor will then be force to that position.  So, after powering back up, the machine is no longer in the same position it was in when powered down, and the error can be up to 2 steps off in either direction.

Regards,
Ray L.
Regards,
Ray L.

Offline Overloaded

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Another note,
  Many lower end stepper machines with no switches, using the bump method is plenty close enough either way.
Similar in accuracy to the reference mark on the table (by eye method).
Most of these type req setting the Part Zeros at setup anyway.
All it's basically for is to be able to enable the soft limits to keep from loosing the part ref.
The way I see it anyway.
Might be missing something also,
Russ

Offline Hood

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Ok Ray good to know, not that I have ever used that method but I have seen a lot that do.
Hood

Offline Hood

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Russ, the main use of referencing for me is so I can be sure I can get to the exact same place the next time I switch the machine on or enable the drives after they have been disabled, thats why I use Encoder Index homing as its deadly accurate. On routers etc then I can see it wouldnt really matter so I suppose the stalling against a stop method is fine for them.
Hood

Offline BR549

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Ray(;-) How far off would the machine be at 2 steps IF the steps per were 2000 ?  1/2 of a tenthousandth??

Most cheap micro switches switches are off far  more than that.

In 99% of the cases IF the machine came back to within .010" no one would know it.

(;-) TP