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Author Topic: How to use Z soft limit with the Tool Length offset?  (Read 1538 times)

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How to use Z soft limit with the Tool Length offset?
« on: February 23, 2017, 01:57:48 AM »
Hi Mach3gicians,

   Mach3 Newbie here, i am doing my initial mill setup and i cannot figure what is the correct way to setup the Z soft limit (other axis are easy).


I want to use the Z soft limit to avoid my end mill to crash with the  table. My tools have a big range of length.

The Z soft limit is in machine coordinate, but for a reason i don't understand (explanation welcome) the soft limit in Z do not add the "tool length offset" before evaluating the trigger condition.
As a result, Z soft limit need to be manually updated after each tool change. Otherwise


if my current tool is shorter that my "reference tool" the soft limit will trigger with the endmill very far from the table.
if my current tool if longer, the soft limit will do nothing and i will get a big hole in my table.

In all case, it really feel awkward...

Do anybody know a way to add some "tool length" awareness to the soft limit?
Thank a lot in advance
Sylphio

Offline Davek0974

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Re: How to use Z soft limit with the Tool Length offset?
« Reply #1 on: February 23, 2017, 02:16:06 AM »
Forget the tool length and offsets.

turn off soft limits

Set your physical hard limits first and make sure they work.

then if using combined limits and home switches you can now ref the machine.

next, jog to say 3mm away from the axis lower limit, the machine DRO reading is your axis soft limit so enter that into soft limits for that axis, then jog to the other end say 3mm away from the limit switch and get the machine DRO reading again, enter that into your soft limit table.

save the soft limits data

now turn on soft limits and you should be able to jog from one end to the other without hitting a limit switch at full rapid jog speed, you may need to fine tune the settings a little.

thats all thats needed.

tool length offsets affect the work origins NOT the machine origin so have no effect on soft limits at all.

:)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: How to use Z soft limit with the Tool Length offset?
« Reply #2 on: February 23, 2017, 02:57:58 AM »
thank for taking the time to answer.

great,  you just confirmed that I properly setuped my soft limit. thank.

this method work fine to me for everything with the big exception of the low z axis limit.

maybe I miss something but , in your example, a 10 cm end mill will crash with the table 9.7cm before hitting the softlimit (I suppose the limit switch at table level). so, I need to update the z low limit after each tool change or accept the fact that I get no low-z side protection.

I am right?
« Last Edit: February 23, 2017, 03:02:15 AM by Sylphio »

Offline Davek0974

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Re: How to use Z soft limit with the Tool Length offset?
« Reply #3 on: February 23, 2017, 04:54:48 AM »
No,

once set you should never need to change the soft limits unless you physically move your hard limit switches.

Yes, if you fit a longer tool after a shorter tool, it WILL crash IF you tell it to go too low - this is life in the world of CNC - YOU are in command of the code that tells the machine what to do.

IF that code is written properly AND your machine is setup correctly for the job in hand, the tool will NOT crash the table :)

You need to know exactly what your code is going to do with whatever tool is fitted BEFORE pressing the start button or things will get expensive very quickly - we have all been there, i busted probably £100 worth of end mills in my first week after i built my milling machine, now it rarely happens, just chalk it up to learning.

There are very few safety nets in CNC - the machines are dumb servants and merely follow your command - you must be in control.

Having said that, it's a blast when it all works - what a ride :)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: How to use Z soft limit with the Tool Length offset?
« Reply #4 on: February 23, 2017, 08:31:27 PM »
Agree, we need to be careful, and you can crash stuff for a lot of reason.

I just find it strange that this feature do not exist. Just allowing to add the tool offet to be optionnally added to the low-Z soft limit would have nearly completely eliminated one potential source of crash.

Offline Davek0974

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Re: How to use Z soft limit with the Tool Length offset?
« Reply #5 on: February 24, 2017, 02:17:29 AM »
Yes but in reality, it very rarely happens.

There are many "checks" that could be put into play but it would add layers of things to go wrong and stop a system from running for no reason.

It is what it is :)

On my screen-set there is a tab called Limits - it shows the extents of travel being called for in the code loaded - i always check that screen first, if i knew my material was 3mm thick and the z axis had a limit of -5mm I know something is wrong and I can fix it - if the machine fixed that for me i would happily be turning out bad code thinking i was good.
« Last Edit: February 24, 2017, 02:20:17 AM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.