Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: neuman5022 on July 24, 2011, 10:32:08 PM
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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
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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.
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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
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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
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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.
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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
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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.
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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)
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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.
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thanks a lot Tweakie - now it looks better :-)
Seems more logical then to use only negative ones.
Another lesson learned today :-)
Cheers
Isaac
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thanks a lot Tweakie - now it looks better :-)
Seems more logical then to use only negative ones.
Just remember that when you ask for help, Tweakie's the only one that will know what you're talking about, because everyone else does it the "normal" way. ;)
Note that some Auto Zero macros (and I'm sure others as well) assume Machine Z zero to be the top of travel.
The one in my screenset is done this way to make it act the same on all machines. If they don't follow conventional wisdom :) there's really no way to know where it's safe to go.
But if you don't use any 3rd party macros, you're free to setup your machine any way you want. :)
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Sorry Isaac and Sorry Gerry,
I read the Manual and as I recall, it says that max Z is set to zero and everything else is a negative value but in practice this is not logical. The convention should, in my opinion, follow the way in which we use the machine with positive values as well as negative ones.
I can't help being weird - I was made that way. ;D
Tweakie.
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Hi again guys
Sorry for the late response.
I thought maybe we CAN have it both ways.
Since I have no motors hooked to my PC - I emulated 3 keys to serve as homing switches.
I have set the soft limit on the home/limit tab to min -40.00 and max 0.00 so the machine's coordinates will have only negative value. Then I zeroed the work limits at some point - and I can jog it to a positive position (only the work DRO's)
Will be interesting to see if this works with the G-code for absolute co-ords though ???
In any case - thanks again for your support
Isaac
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In the real world it is used BOTH ways. It just depends on what you require.
SOme use the top of table as zero and the positive values only and they represent the true Height of the part being machined as the bottom of the part is at Zero. This is used a lot with 3d work and rotary work as it is very easier to fit the parts to the material.
Most set the top of material as Zero. Then all moves are negative. The true hieght of the part is NOT apparant and you must know where you are in relation to the bottom of the material to get the true part height correct.
There is NO correct way so to speak. BUT this has nothing to do with homing as homing is a seperate function based on MACHINE position not work position.
Most modern Cams allow it both ways so it must be widely used both ways(;-)
Just a thought(;-) TP
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Hi BR
Thank you for your comments.
I guess the MACHINE zero was meant to be set at the top of the Z axis movement as a safety issue - so if something goes wrong - the machine will go to the home position hence clearing any obstacles.
The work zero will be either on top of the material or it's bottom as you suggest. Some programs I have seen are already taking care of the height issue by offsetting for zero, safe zero and depth of cut (Cut2D for example)
I will probably use the top of material as work zero since most of my jobs are full material cut and engraving.
Cheers
Isaac
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(;-) Machine Zero can be anywhere and in many cases it is NOT at teh end of an axis it can be in the middle. It is not tied directly to home(G28) as HOME can be anywhere as well. HOME(G28) is just referenced off of Machine zero.
The only direct link to machine Zero is the G30 that will take you to Machine Zero in MACH3 gcode.
The Machine coordbase is there so Mach knows where it is at in relation to ANY offset that you may require. Once set the OP cannot change any value the most they can do is Zero it another location(not always a good idea)
BUT don't let that confuse you(;-) Yea Right. Just set up the machine as you want it to be and sling some chips. Once set up it will always behave as you set it up. If you find out you don't lke it that way, simple change it(;-) that is what config and setup is all about.
If you want it to conform to the perceived standard do so(;-) or not(;-) your choice.
BUT if you set it up weird so you are the only one that can understand it THEN only you may be able to understand it. Catch 22 The rest of us may just say HUH??????
(;-) TP
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One other thing that may be worth mentioning is if you have seperate home switches they can be placed anywhere on the axis travel and you can still set Machine zero up to be at the extents by using the Home Off entry in Homing and limits. I do that on my mill and lathe, the lathe because the X has to home mid travel due to front and rear turrets and the mill as I wish the Y to home with the table fully towards me for easy access to the vice without having to jog after homing.
Hood