mach3 soft limits

[Daveo]

hi all
so far i have all my cnc built and i am setting up mach3, motors done,spindle done but i am pulling my hair out trying to work out the soft limits.
i read it was better to set up the soft limits first.
i have measured my X Y and Z and put all the settings in to homing and soft limits but each time i click on the soft limit button it fails.
any help please.
thanks daveo

[Cube3]

Hi,

Give us a little more info so that we can help. What are your settings? What do you mean by the soft limit button fails? What is the machine doing or not doing successfully?

Sent from my COL-L29 using Tapatalk

[dazp1976]

Watch these.
https://www.youtube.com/watch?v=zFk_U3yqrks
https://www.youtube.com/watch?v=If3g6bWVlbM

There's loads of good tutorials out there.
Some brief short ones make confusion worse.

Patience and learn.

[JAZZCNC]

Soft limits work from Machine Zero. So if you haven't got home switches installed and enabled then you will need to "Ref All" before soft limits can work. Then the Soft limit will be from the point you Zeroed at. You need to be careful here because let's say you "Ref All" at some point along the axis travel but you have set the soft limit value to be the length of your full travel then it will crash into the ends because it thinks the soft limit is further away. The soft limits are only safe if you have Home switches fitted and have homed the machine first.

[Kitwn]

My simple brain tells me the sensible order of events is:

1) Install limit switches. This prevents any damaging crashes from here on.
2) Set up homing. Separate switches if you must but using the same limit switches works for me and reduces cost and complexity.
3) Set up soft limits. This prevents any annoying, unwanted hitting of the limit switches and allows you to jog the gantry out of the way by simply letting it run to the soft limits.

As Jazz says, soft limits have no meaning until the gantry is homed so 1 & 2 must come before 3.

[dazp1976]

I haven't got physical limits installed on my mill yet so I only have soft limits to rely on.
I am in the process of dealing with physical ones atm.
I have to be much more careful to prevent crashes.

Home on my Z is at the top of column. It has another 71mm left going up and 255mm down. So soft limits are +70 & -254.
Y is table centered and X off center so softs are Y-92 &+ 92 (185mm total travel). X+175 & -320 (496mm total travel). Leaves 0.5mm either end.

The BIG problem is if/when you lose steps or lose position after a jam.
If I lose my home I lose my limits. I have to mess around finding my home again by hand and test all the limits before I can run again safely.

With physicals I could just jog to the switches and reset.

[Kitwn]

With physicals I could just jog to the switches and reset.

That's the whole point. Hit the "Home All" button and watch the machine do the work for you. It won't take long for you to save the amount of time spent on fitting the switches.

[JAZZCNC]

The BIG problem is if/when you lose steps or lose position after a jam.
If I lose my home I lose my limits. I have to mess around finding my home again by hand and test all the limits before I can run again safely.

You shouldn't be losing steps at all, if you are then you have motor tuning set up wrong or the machine is sticky. Hitting the e-stop while traveling fast lose you position.

I'd fit home switches before limit switches every time or better still have them share SW.

[Daveo]

hi
that was the problem it would not zero even after hitting Ref All, it must of been a bug as i have loaded a new profile and its all working now but on reading the last few posts i think i will add some physical switches
thanks daveo

[Kitwn]

I'm not familliar with MACH3, only LinuxCNC but your last message gives the impression that you are missing the point that "Ref All' sets the current position of the machine to zero, wherever it happens to be (if I interpret Jazz's comment in reply #4 correctly). There is nothing to tell the controller where the machine is actually positioned so 'zero' will be a different place every time. The point of homing switches is that the machine moves blindly towards the switches and as soon as it hits them it suddenly knows where it is and can call that 'zero' which will be the same place every time. Manually hitting 'Ref All' becomes redundant and should never need to be done once propper homing is installed.

Soft limits put a limit on how far the machine can move from zero so if zero is wrong soft limits will not help you prevent crashes. Once homing is working correctly soft limits become your best friend but whoever told you to set them up first has sadly wasted a lot of your time. I stick by my preferred order of events in post #5

Good luck getting everything working.

Kit

[JAZZCNC]

Manually hitting 'Ref All' becomes redundant and should never need to be done once propper homing is installed.

Every thing you said Kit was spot on except for this bit, but your excused with you being a Linux Geek..:beguiled: But I'll clear it up for the sake of those new to Mach3.

Hitting REF ALL works in 2 ways depending on Home Input settings. If the HOME inputs are NOT enabled then REF ALL will ZERO the HOME position where ever the machine is parked.
But if the HOME Inputs are enabled then REF ALL will start the HOMING Sequence(macro) and the machine will set off looking for switches.

So you MUST use REF ALL to set MACHINE ZERO which is the bit KIT doesn't know with not using Mach3, just be careful if you have enabled the HOME inputs as the HOMING sequence will set off and Mach3 as no clue if switches are fitted or not so will keep moving until it hits a something.!!

Not fitting HOME switches is crazy unless you have repeatable hard stops because they are life savers on jobs when a cutter breaks or power goes off in middle of a job etc. They allow you to get back to zero or any point in a job easily and accurately. They also allow you to break large jobs into separate sessions at the machine ie: over a few days and repeatably get back to WORK ZERO or a line you stopped the job at.!

[Kitwn]

Thanks for clearing that up Dean. I've never used MACH3 or built a machine without homing switches.

The ability to accidentally wipe out all your homing references with one button push would be a bit silly and I should have guessed it's not the sort of thing a man as clever as Art Fennerty would have written into his software.

[Daveo]

well thats makes sense, i will fit limit switches as well as running the soft limits, thanks for all the advice
daveo