First post on the forum so go easy please.

I'm a newbie to the CNC world and have some rather simple questions I hope about homing and limit switches when setting up MACH.

- Are the "Soft Max/Min" set from the distance of the Limit switch or Home switch?

- Is the "Slow Zone" the distance before it hits the Limit switch or the Home switch?

- Is the "Home Off". used to set a distance from the physical Home switch?

I realize that MACH enters default settings but I was hoping someone might share what their settings are and how they came to those conclusions.

Thanks for any and all input..

Adam,

It all depends on your setup.
ie whether you share Home and Limit switches  or have separate home switches.

Soft Min and Max are normally set to..
X and Y axis it would be 0 for Min and the travel of your axis for Max
Z  it would be 0 for Max and your axis travel for Min but as a negative value.


Slow zone is the distance the axis will start to slow down when jogging if you are heading towards a soft limit.

Home Off , often people think it means the distance the axis will back off the home switch during homing but that is not the case. Home Off is actually short for Home Offset. What that means is when you home the machine coords of Mach will be set to the value you have in the Home Off entry.
Normally you will have 0 in there however if you home to the positive end of the axis then you would enter the distance the home switch is away from normal machine zero, ie fully negative. What would happen in that case is when you home machine coords would be set to the Home Off value and thus Mach knows Machine Coords Zero is at the opposite end of the axis.
Another situation where you would use Home Off is if you have separate home switches and they are inboard a bit from your limit switch, say for example your limits are at the extent of the axis but your home switch is 50mm inboard, you would then set a Home Off value of 50. When you homed the machine coords would be set to 50 and thus Mach would know it has a further 50mm of travel in the negative direction before it reaches the true machine zero (limit switch)

Hood

To expand a little...
When you Home the machine to the Home switches, Machine Zero is set. The Softlimits are in relation to Machine Zero.
What I do, is set my Home Offset to a small negative value, say -.5".
So after homing, when my home switch is then acting as a limit switch, I can go to the zero position on the axis and still be .5" away from the switch. If you then set softlimit min to 0, the machine will stop before it gets near the physical limit (home) switch.

Thanks for the reply's, a couple of follow ups..

My setup consists of a slaved A Axis on X Axis and I'm sharing Limit and Home switches.

"When you Home the machine to the Home switches, Machine Zero is set. The Softlimits are in relation to Machine Zero."

Would the benefit to a Softlimit come for users with a single switch on each axis, machine Zero?

"So after homing, when my home switch is then acting as a limit switch, I can go to the zero position on the axis and still be .5" away from the switch. If you then set softlimit min to 0, the machine will stop before it gets near the physical limit (home) switch."

Is this to keep it from triggering the Limit switch since you share Homes and Limits?

"X and Y axis it would be 0 for Min and the travel of your axis for Max
Z  it would be 0 for Max and your axis travel for Min but as a negative value."

Is the travel determined by a physical measurement or simply by jogging the axis and determining the length from the Home switches on the axis?

Slow zone is the distance the axis will start to slow down when jogging if you are heading towards a soft limit.

Does this hold true for all movement weather it be in GCode or using a pendant, etc.?


For the Z axis, "0" is that determined to be the absolute "0" without bit - trying to get a mental picture?

Adam,

Thanks for the reply's, a couple of follow ups..

My setup consists of a slaved A Axis on X Axis and I'm sharing Limit and Home switches.

"When you Home the machine to the Home switches, Machine Zero is set. The Softlimits are in relation to Machine Zero."

Would the benefit to a Softlimit come for users with a single switch on each axis, machine Zero?

Having two switches on a slaved axis will allow you to auto square the gantry on homing but Ger is the guy to keep you right on that score as he uses routers with slaves I think, I dont.

"So after homing, when my home switch is then acting as a limit switch, I can go to the zero position on the axis and still be .5" away from the switch. If you then set softlimit min to 0, the machine will stop before it gets near the physical limit (home) switch."

Is this to keep it from triggering the Limit switch since you share Homes and Limits?

This one is really for Ger as it is his postings you are responding to however the way Mach homes is it moves onto the switch then backs off and when the switch closes it sets that as home. So you should never hit the switch as soft limits will stop that from happening, that is assuming the slow zone has been set correctly. The way I do that is set a value for the slow zone then move off a sufficient distance to allow full rapid to be reached when jogging back to the switch. I then jog back and if the limit gets hit I increase the slow zone a bit and try again. If it doesnt I reduce and try again, do that over until I find the sweet spot.

"X and Y axis it would be 0 for Min and the travel of your axis for Max
Z  it would be 0 for Max and your axis travel for Min but as a negative value."

Is the travel determined by a physical measurement or simply by jogging the axis and determining the length from the Home switches on the axis?

You can put into Machine coords and jog until you trip the limit then you have the value you need to enter, well it will be slightly less than the DRO shows it to be.

Slow zone is the distance the axis will start to slow down when jogging if you are heading towards a soft limit.

Does this hold true for all movement weather it be in GCode or using a pendant, etc.?

Pendant yes, G Code I dont think so, however G Code will give you a soft limits warning when you press start, it will also tell you which axis the soft limits are affecting.

For the Z axis, "0" is that determined to be the absolute "0" without bit - trying to get a mental picture?

The softlimits are in respect to axis travel so it has nothing to do with whether there is a tool in or not.

Hood

Would the benefit to a Softlimit come for users with a single switch on each axis, machine Zero?

I don't know what you're asking here.
Personally, I don't use Softlimits.

Is this to keep it from triggering the Limit switch since you share Homes and Limits?

Yes, this gives you a little more room to work. I run my parts at machine zero, so this gives me room to move in the negative direction a little.

Adam,

Link to a tutorial on setting up a basic 3 axis mill. See pages 11-14 about switches and homing to suppliment replies already made.
http://www.machsupport.com/forum/index.php/topic,26252.0.html

Here is a link to Mach videos which you should find of value.
http://www.machsupport.com/videos/


A few general comments:
1. Switches are used to provide for a repeatable location to a point within the possible movement of the axes.
    One could  have no swithes or some combination of switches.They can be setup and used in a number of ways.
    In general they automate setting up the machine ie;  for a machining job, positive restriction of axis movement, defining to Mach some point.
    
2. The controlling software ( MACH ) does not know anything about some point on the machine, how far an axis can move in a direction, etc.
    The user must define point / points to the controller so that Mach can associate the machine point, tool point, program point for maching tasks.
    Hmm...lots of points and notice they were only general descriptions!

3. One needs to be carefull in the thinking about switches. When setting them up the focus seems to be on the mill table / z spindle travel or
    the carriage for the lathe. That thinking is one part of the overall consideration for setting some points.

4. You will find that the thought process is different when presented by different manufactures or say Smid ( an author on CNC, BTW,
    his books are an excellant resource and has one on machine setup). They define terms in a very specific way for understanding and
    generaly correlate the points to how gcode is appied. You may want to have a look at Fanuc's info.

5. A few comments on wording which is important.
   A machine has extreme travel limits. A point within the limits must be defined to the controller ( Mach3) so that all other movements can be associated.
  That point is machine zero and as such is known, fixed and defined. Home is just a point within the limits and it can be anywhere, but, home is usually
  machine zero. So home is used interchangeably with machine zero many times. Referencing is used to describe the condition where one has moved to
  some point and done something to tell the controller that the current position is machine zero or home. Homing can be done automatically, using the MDI,
  or manually and used to describe the motion of returning to machine zero. Fixture offsets are defined locations away from the home position.
  Fixture offsets are not to be confused with tool offsets. So an offset is just some distance from a point and needs to be always clarified.


6. I attached some info from a Fanuc Manual that you may want find informative. Look at thee figures and associated text that appies to them.
Give you a flavor about offsets .......

RICH

Many thanks for the additional information.

With your additional comments its helping fill in some of the blanks.

I'll now just need to dig in and get a feel for how the machine reacts and what the sweets spots are...

Adam,

Adam,
I don't use switches on any of my machines, but, I do use soft limits, not much for the mill but mostly on the lathe.

Just get them installed and configured. Then play around since you can always reconfigure them to your liking or improve
based on comments from users.

Have fun,

RICH

Have a follow up ?

I use SoftLimets, work nicely(No switch), probs is that then i am near the end, it dont slow down to ie 5% , it just run at same speed and stop at Softlimets settings.. How or why will it not slow down?
Using RnrMotion card via USB.