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Offline ger21

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Re: Z axis help
« Reply #10 on: July 26, 2011, 08:10:48 AM »
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. :)

2010 Screenset

JointCAM Dovetail and Box Joint software

Offline Tweakie.CNC

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Re: Z axis help
« Reply #11 on: July 26, 2011, 08:18:50 AM »
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

« Last Edit: July 26, 2011, 08:20:59 AM by Tweakie.CNC »
Re: Z axis help
« Reply #12 on: July 29, 2011, 03:43:23 AM »
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


Offline BR549

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Re: Z axis help
« Reply #13 on: July 29, 2011, 10:51:11 AM »
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
Re: Z axis help
« Reply #14 on: July 30, 2011, 12:10:43 AM »

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.



Offline BR549

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Re: Z axis help
« Reply #15 on: August 01, 2011, 04:25:03 PM »
(;-) 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

Offline Hood

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Re: Z axis help
« Reply #16 on: August 01, 2011, 05:43:23 PM »
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.