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Author Topic: Z-Axis Dro - Odd behaviour?  (Read 2783 times)

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Offline Davek0974

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Re: Z-Axis Dro - Odd behaviour?
« Reply #10 on: January 17, 2016, 03:42:14 AM »
Yep, IMHO, the hard part is building a machine capable of doing CV at all speeds, if it even exists?

My latest build gets close (ish), I think to improve I should have gone with servo motors and closed loop motion control, would likely have to mortgage the house to pay for it all though :)

In reality, CV is impossible though surely? The machine MUST come to a stop to do a sharp 90deg corner??
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Z-Axis Dro - Odd behaviour?
« Reply #11 on: January 17, 2016, 05:33:21 AM »
Quote
In reality, CV is impossible though surely? The machine MUST come to a stop to do a sharp 90deg corner??

Not really as you can, I would imagine, do as you would with a mill or router. Roll round the sharp bend at the radius of the cutter, or kerf width in the case of plasma. That means you do not have to stop as you would in Exact Stop mode.
Of course it will never be exact but if the acceleration is decent on the machine it will be more or less undetectable.

Hood

Offline Davek0974

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Re: Z-Axis Dro - Odd behaviour?
« Reply #12 on: January 17, 2016, 06:54:05 AM »
Good point, I don't run a mill or router but have seen the diagrams of rolling around a corner producing a point, I guess it would be the same, thanks.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Davek0974

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Re: Z-Axis Dro - Odd behaviour?
« Reply #13 on: January 17, 2016, 07:02:00 AM »
Back to the topic, the new, reduced set-origin button works perfectly, setting "G28.1 No Initial Move" to OFF has made the Z rapid down to the Z value in the G28.1 command - brilliant.

A short video of the final setup making a couple of cuts...
https://youtu.be/FV6WpuQjFE0

That just leaves the fact that if the THC does not finish at zero as it started (which it never does) the difference between my 15.00mm safe height and the final THC adjustment is what shows in the Z DRO even though the machine was told to go to Z15.00 at the end.

Now, I have a theory -

The THC adjustments DRO is updating the Z DRO AFTER the machine has finished - the cut completes, the machine goes to Z15 as commanded but then the THC system adjusts the Z DRO to a wrong value.

I see no reason why  the THC should deb adjusting the Z DRO though, I will post this again on the CandCNC forum, probably won't get anywhere again though.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Z-Axis Dro - Odd behaviour?
« Reply #14 on: January 17, 2016, 01:15:00 PM »
Interesting  method for deployment of  the switch, might be worth considering something similar when I build mine :)

Hood

Offline BR549

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Re: Z-Axis Dro - Odd behaviour?
« Reply #15 on: January 17, 2016, 01:54:52 PM »
Looks good from here(;-) Good Job. One thing I do notice is it may be a problem with a heavily nested cut and using an offset probe as teh probe could easily end up in a hole from a previous cut. Maybe consider a compromise of your earlier design where teh Air cylinder was on a slight angle to help slide teh probe tip under teh Torch tip ???

Also keep teh sliding Z as a backup to the touch probe. Even though I have RARELY ever seen teh G28.1 fail to cycle. But a backup would be nice to have set  up as a safety.  IF you do not have a breakaway torch mount each time you crash the head and break the torch insulator sleeve it is a $100 bill.

BUT then you get to learn how to get GOOD at repairing those sleeves (;-).

(;-) TP

Offline Davek0974

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Re: Z-Axis Dro - Odd behaviour?
« Reply #16 on: January 17, 2016, 02:13:04 PM »
Thanks

I did think of the switch falling into a hole but the arc it travels is very small and lands exactly where the torch would, I have been messing today and tried tight spacings, near-edge etc and all worked fine, if it would work with the torch, I think it will work with this. A true edge-start might be tricky, don't know yet, never done one.

The sliding Z is staying and i will be moving the limit switch wiring to the e-stop circuit as the limits do nothing when g28.1 is running, luckily I wired every switch with its own cable back to the control cabinet.

Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline BR549

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Re: Z-Axis Dro - Odd behaviour?
« Reply #17 on: January 17, 2016, 02:19:18 PM »
IF you have ever watched a real comercial plasma cutter OR laser cutting thin sheet goods  they are WICKEDLY fast on Accelleration. Most use an Scurve planner that makes it not only wickedly fast but very smooth . Almost ALL runs servos. There are also designed with very low inertia Drives and gantries and are very rigid as well.  

Now that said A well planned Mach3 CNC plasma is a GREAT machine for the money and the normal useage for the average users.



Offline Davek0974

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Re: Z-Axis Dro - Odd behaviour?
« Reply #18 on: January 17, 2016, 02:42:32 PM »
IF you have ever watched a real comercial plasma cutter OR laser cutting thin sheet goods  they are WICKEDLY fast on Accelleration. Most use an Scurve planner that makes it not only wickedly fast but very smooth . Almost ALL runs servos. There are also designed with very low inertia Drives and gantries and are very rigid as well. 

Now that said A well planned Mach3 CNC plasma is a GREAT machine for the money and the normal useage for the average users.


Low inertia, high rigidity is the holy grail I think, very hard to do.

Personally I am very pleased with my table, for what it cost i think it's amazing, even more so when, after a couple of days messing around I have improved it ten-fold :)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives