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basic questions by newbie
« on: October 13, 2014, 11:40:01 AM »
I'm thinking of buying a small mill/engraver and have started playing with the demo versio9n of mach3 and have some basic questions.
I'm running mach3 without a machine connected, parallel port disabled.
I Have a small gcode program that is a 1" square. It goes like this:
G41 D125
T1 M6

I start mach3 and hit reset, then load the cnc file. I turn on machine co-ord's and referece (zero) all axis, turn off mach co-ord's., then hit cycle start.
Watching the program run, z axis goes down half inch, but watching the DRO's, the x axis doesn't go to 1", only makes it to .9830", the y axis goes all the way to 1.000"
Why does the x dro stop at .9830"?

Shouldn't the dro's actually indicate movement of 1.125", since I have programmed a G41 D125 ? I also have tool1 set as diameter .125"

Hopefully soon I'll have a machine connected and buy a licence. I hope this forum is the right place to ask these questions.

Offline ger21

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Re: basic questions by newbie
« Reply #1 on: October 13, 2014, 12:02:48 PM »
I turn on machine co-ord's and referece (zero) all axis,

Referencing and zeroing are two different things, which are you doing? And turning on machine coordinates does nothing for you. If you reference the machine (Ref All Home), the machine coordinates are zeroed whether they are active or not.
If you're actually trying to zero the axis, you can't zero machine coordinates. Machine coordinates can only be zeroed by referencing.

G41 D125 means to use the diameter of tool #125, not tool #1.

You either need to enter a diameter of .125 in tool #125, or, use the P word with G41.

G41 P0.125

You also need to use a lead-in move with G41/G42, or you'll get unexpected results.

I'm assuming you want to start from 0,0? In that case, don't switch to machine coordinates, just click the X zero and Y zero buttons.
You'll need to modify your g-code to have a lead in move where the compensation is applied.


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Re: basic questions by newbie
« Reply #2 on: October 14, 2014, 02:43:58 PM »
thanks, but I still don't know the reason for the dro problem, if I start the plasma profile of mach3 everything is fine, the mill version has this dro problem.

thanks for the explanation of G41. The kerf handling routines in mach3 would cause problems in case of overlapping kerfs at inside corners. The machines I'm familiar with all handled cutter compensation correctly at the control, I guess thats why mach3 relies on cam software. I have hundreds of cnc plasma cutting gcode artwork, but they all need the controller to add compensation without gouging the corners.
So far I've enjoyed playing with mach3, hope to have a machine soon (to add to my toy collection).

Offline Hood

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Re: basic questions by newbie
« Reply #3 on: October 18, 2014, 06:08:24 AM »
The DRO issue may be due to the steps per unit you have, ie the axis is the closest it can get to that point without exceeding it due to the minimum step size.