Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: wisconsinjimmy on February 22, 2018, 03:27:05 PM
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Hello all,
I have my Hard Limit Switches glued to the chassis and wired in series and when any of the limit switches are contacted the machine stops. X travel is 50.0000mm and my Y travel is 60.0000mm these numbers are when the machine just moves the switch.
Now how do I set the soft limits? On the X travel do I start at 50.0000 mm enter this in max and 00.0000 in min and hit enter.
Best Regards and God Bless
Jim G
Cushing, WI
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I always start a few mm away from the switches and see how it goes -its easy to change.
Yes, 0mm is usually the homing end and the other would 50 or 60 in your case, make sure the table is in the middle area, set the values then turn on "soft limits" and try jogging into the end, a little fine tuning and thats it.
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I just cannot seem to get it through my head, I have been watching You Boob and it all seems so easy although each person has their own way.
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Hi,
soft limits rely on the machine being referenced or homed. How does your machine do that?
Craig
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Settings (ALT6) Tab
X axis, I told the machine to move 20 mm and all I got was 10 mm pondering this huge discrep the machine must have moved the X only 10 cm .
I do have a steel flat ruler taped to the bed so as to get excellent readings
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Sounds like your steps-per is out maybe, if its only moving 50% of the instructed distance, you need to do some tuning before messing with soft limits.
As Craig said above, you cannot use or set soft limits until the machine is referenced or homed.
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Hi,
you are trying to run before you can walk.
If you can't jog or MDI accurately 10mm say then who cares about whether the limit switches work? Until you can home your machine then
soft limits are meaningless.
Start by reading:
http://www.machsupport.com/wp-content/uploads/2013/02/Mach3Mill_Install_Config.pdf (http://www.machsupport.com/wp-content/uploads/2013/02/Mach3Mill_Install_Config.pdf)
Get your axes moving the correct distance by calculating or measurement to set the 'Steps per Unit' setting in the motor tuning page.
Craig
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Hi wisconsinjimmy,
are you a country person? I am and am therefore comfortable with rural analogies.
Lets say you have an automatic tractor and you wish for it to plow a rectangular paddock. You could build 'limit switches' on to the tractor so it knows when it
hits the fence but really its too late, its hit the fence, the switches may stop it from wrecking it but the switches haven't helped it navigate around the paddock
to do its job.
Imagine that somewhere in the paddock there is one rock which pokes out of the ground. If you manually drive the tractor to the rock and then program the tractor
'you are at the rock', and the boundaries of the paddock are 210 yards to the North, 65 yard to the South ...etc. Now the tractor knows where it is and if you let it go to
work it will know where it is based on the distance and direction its travelled since it was 'at the rock'.
If you had mistakenly programmed the tractor to plow out to 250 yards North of the rock the tractor 'soft limits' will say NO, the boundary is 210 yard North, I can't
go where you want me to go so I'll stop.
That is the essential meaning of soft limits. It absolutely relies on a place 'at the rock'. That place must be exactly the same everytime the tractor is required to plow
that paddock because only then do the boundaries make sense.
For this reason I always argue that home switches ('the rock') are more important than limit switches. It seems that a lot of people disagree with me but I happen
to know some very experienced CNCers who do agree and don't even bother with limit switches. Good reliable home switches and soft limits are the way to go.
Craig
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I fully agree limits are pointless on a machine with steppers as they will stall if soft limits fail or were turned off, but on a servo driven machine i would prefer hard limits wired to the safety circuit not the controller - if an axis runs away it will kill the power.
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Hi Dave,
I'm not decrying the use of limits but rather that homes switches are more useful to actually do a job.
I am lucky enough to be able to sail keel boats regularly as part of a race crew, I guess the pic which is attached to my posts rather suggests that the sea is the best
recreational resource we have. Anyway people often ask about safety equipment like VHF, EPIRB and a liferaft. All of those things come into play when you've already
sunk the boat....I call safety those things that you do to PREVENT the sinking of the boat in the first place! Things like up to date charts, knowing how to read them, how to
navigate WITHOUT GPS, what techniques and sail trim you can employ when or if a gale strikes....you know the skills of sailing!
In like manner I consider limit switches to be safety devices of last resort and home switches the first port of call to avoid crashing into the limits.
Craig
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Craig,
This is where I get totally dumbfounded, I think the LIMIT switch is the one you install at the end of an axis to shut the machine off before it can cause damage to itself.
Home switch is what Mach3 controls and is installed digitally.
I also need some help on this LIMIT switches, I am using a HobbyCNC control board and pin 13 for my LIMIT switch also I should mention that I am using a UC100 instead of the Parallel cable. Where do I set my limit switch in Mach3
Thanks for the help
As always
God Bless
Jim Ganley
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Yes LIMIT is a physical switch at the end of each axis travel, its optional, you could fit it as just a HOME switch or let mach3 use the limit as a combined home and limit switch.
I would install as a home switch as you only need one switch per axis and then setup soft limits.
If using limit switches you need one at the end of each axis.
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Hi,
have you worked out how to tune the motors yet?
Limit and home switches are pointless until you've got that right.
Craig
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I have went to the Setting Tab and moved my y axis to the center line of the table and just off the mechanical limiter switch, I then entered 14mm hit OK and the y went 7mm 1/2 of what I want?
I have moved the X to the left and just touching the limit switch, entered 14mm and got 14 mm and Mach3 asked if I wanted to set the the X to 4000 steps per Unit? I replied yes,
What is wrong with the y.
I have moved Z to the top and dropped it -9mm and that was acceptable, Z axis will be set to 1800 steps per.
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so you set the x and not the y?
you need to repeat the adjustment for the y axis, that should help
when you go to auto setting there are buttons for each axis - choose y and try that
once you get them working you need to repeat the settings with as much travel as possible - 14mm is far too short for accuracy
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So what I want to do is use the full length and width of the table/
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Its always best when setting distances and checking them to use as much travel as you can measure accurately - it reduces errors/increases accuracy.
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I am right in the middle of this very same struggle. However, after messing with the “steps per” I’m Mach for a few hours trying to figure out why my axis’s would only move half as far as They should. I found out that the the drivers have a half step dip switch. I flipped that and then the distances work great. I am now trying to figure out my home/limits switches. I will have to start a new thread for myself and try and get a little help. with that portion.
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Hi,
you would be advised to leave half-stepping active and double the steps per unit setting. In fact just about all stepper powered CNC axes are operated at some sort
of microstepping, commonly 8 microsteps per full step or 16 microsteps per fullstep.
Its nice to think that the resolution improves as you introduce microstepping but the truth is the gain is illusory. The real advantage is smoothness of motion.
Midband resonances are very much reduced with microstepping.
If your driver allows 8 microstepping then increase the steps per in Mach by a factor of 8 as well.
Craig
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Hi,
you would be advised to leave half-stepping active and double the steps per unit setting. In fact just about all stepper powered CNC axes are operated at some sort
of microstepping, commonly 8 microsteps per full step or 16 microsteps per fullstep.
Its nice to think that the resolution improves as you introduce microstepping but the truth is the gain is illusory. The real advantage is smoothness of motion.
Midband resonances are very much reduced with microstepping.
If your driver allows 8 microstepping then increase the steps per in Mach by a factor of 8 as well.
Craig
I didn’t know that. Thank you fo the information. I will try that