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Z axis help
« on: July 24, 2011, 10:32:08 PM »
Hello all

This is my first post - so you know I am a real noob :-)

I am confused with the Z axis zeroing and direction of movement:   (I will use this with a router)

In Mach 3 video - it was recommended to set the max value to zero and the min value to the actual travel of the z axis. The example was   -200. So I understand the logic is to home the z axis to the top as a safety issue. So when cutting a job - I will jog the z axis down to the work piece and zero it - then to cut the material my logic says to put negative numbers. (say -0.1)

However on the sample programs, I see some positive numbers and when trying to execcute -  I get the soft limit warning.

In the Multi pass wizard - (which I will surely use) all the numbers are positive again, and the video says to put for example 0.75 as a negative value ???

Can someone please help me understand this issue ?

Cheers


Isaac

Offline ger21

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Re: Z axis help
« Reply #1 on: July 24, 2011, 10:52:33 PM »
Quote
I will jog the z axis down to the work piece and zero it........................................................However on the sample programs, I see some positive numbers and when trying to execute -  I get the soft limit warning.

When the top of your part is zero, there should be some positive distance from zero up to the top of your travel. Machines with longer Z axis' will have more positive travel.

Are you homing the machine at the top of travel? The softlimits are in machine coordinates, and if you don't home the Z at the top, then your machine zero may be below the top of travel, thus triggering the softlimits.

Never used the multipass, so can't help you there. But sometimes when entering cut depth, some programs accept positive numbers for depth of cut, even though the g-code will be negative numbers.
Gerry

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Offline Tweakie.CNC

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Re: Z axis help
« Reply #2 on: July 25, 2011, 02:10:28 AM »
Hi Isaac,

Welcome to the forum.

When machining stuff the top surface of the part is usually set to Z Axis zero (0.0000) then any cutting into the work will be a negative number. Many of the free GCode creation programs produce the code this way whilst the 'professional' programs allow a choice of zero position.

Tweakie.


nb. There is a price to pay for any help you get here - you have to teach us all about flight simulators.  ;D
PEACE
Re: Z axis help
« Reply #3 on: July 25, 2011, 08:21:39 PM »
Hi Guys

Thanks heaps for your kind support.

So as I understand it - the machine coordinates can be set for 0.00 at the most top of the Z axis and the negative number will represent the full stroke of the Z axis. When zeroing for the part coordinates - it can get a positive number since it is still in the soft limits area.

The troubles I had with the other program was probably due to the fact he put an absolute code in - hence there cannot be any positve number at all


So much to learn - but I love it.

BTW - I am more then happy to pay the price... :)   

Cheers

Isaac

Offline Tweakie.CNC

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Re: Z axis help
« Reply #4 on: July 26, 2011, 01:37:31 AM »
Quote
So as I understand it - the machine coordinates can be set for 0.00 at the most top of the Z axis and the negative number will represent the full stroke of the Z axis.

Not quite.

On my system (for example only)  Z 0.0000 is at approx. mid point of the full Z Axis travel.

Tweakie.
PEACE
Re: Z axis help
« Reply #5 on: July 26, 2011, 04:35:53 AM »
Thanks Tweakie

I guess you have a good logic for having the Machine cord's at half travel - is there any advantage or good reason for this or this is just your pick ?

Cheers


Isaac

Offline Tweakie.CNC

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Re: Z axis help
« Reply #6 on: July 26, 2011, 04:53:35 AM »
Hi Isaac,

I am not an expert here but it seems that it is just the way it turns out.
With Z 0.000 being the top surface of the work (individually set for each job) then the Safe Z setting within Mach is a positive number as is all the Z Clearance figures calculated by the software I use. It just seems tidy that way.

Tweakie.
PEACE
Re: Z axis help
« Reply #7 on: July 26, 2011, 05:30:45 AM »
Hi Tweakie

Ok - Now I am confused again :-)

With Z 0.000 being the top surface of the work (individually set for each job) then the Safe Z setting within Mach is a positive number as is all the Z Clearance figures calculated by the software I use. It just seems tidy that way.


Are you talking about the Machine coordinates (soft limits) or about the job zeroing ? (work coordinates)






Offline Tweakie.CNC

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Re: Z axis help
« Reply #8 on: July 26, 2011, 05:40:13 AM »
Hi Isaac,

Sorry it is me that is confusing the issue.

My soft limits have Z zero at approx half travel this makes more sense to me as it agrees with work positioning where positive Z is always work clearance.

Tweakie.
PEACE
Re: Z axis help
« Reply #9 on: July 26, 2011, 08:04:15 AM »
thanks a lot Tweakie - now it looks better :-)

Seems more logical then to use only negative ones.

Another lesson learned today :-)


Cheers

Isaac