Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: kharrisonkevin on April 09, 2016, 05:01:13 PM

Title: G53 & G28
Post by: kharrisonkevin on April 09, 2016, 05:01:13 PM
Can anyone tell me why my Mach3, G53 & G28 are doing the same thing. I have another thread called gcode mishaps so you can see what is happening. I can cut anything because may x scale is out and my z seems to act crazy at the first of a gcode run and unpredictable at the last. Can anyone help?
Title: Re: G53 & G28
Post by: mc on April 09, 2016, 05:07:26 PM
Have a read of http://www.mmsonline.com/columns/g28-versus-g53
Title: Re: G53 & G28
Post by: kharrisonkevin on April 09, 2016, 05:38:12 PM
This still doesn't explain why my machine, when I run a gcode run the y axis goes to the proper dro and the x axis dro is short by approximately -.0025. At the first of my run when I start the gcode run you don't know where the z is going to go. The y is fine the x is out a bit. At the end of the run the z axis mite go to zero or try to cut away down into my table. You have to baby sit it all the time and it is inaccurate to say the least. I am just about to take the cutting torch to it and send it for scrap I am pulling my hair out. Help Help.
Title: Re: G53 & G28
Post by: RICH on April 09, 2016, 06:05:18 PM
How about just one fix at a time.

The controller is only doing what you told the controller about YOUR machine and what you tell it to do, so, if the x axis is off, then test the X axis.
Before you do that, calibrate the X axis so the steps per unit are  correct. The calibration is done with axis backlash removed before moving the axis
in the same direction. You can use the calibration feature of Mach to do it or calculate the steps per. Now check for backlash, and if there is any, fix the machine, use BC,
or live with it.

In the mean time, have a read about G28 & G53 in Mach's Manual on how the code is interpreted by Mach.

For now,
RICH
Title: Re: G53 & G28
Post by: kharrisonkevin on April 09, 2016, 06:32:20 PM
Thanks I'm new to all of this but I am trying hard to learn
Title: Re: G53 & G28
Post by: RICH on April 10, 2016, 07:45:45 AM
kevin,
Understand.  The gcode for different controllers are similar, but like language there are dialects.
So consult the Mach Manual when reviewing something based on a different controller.

You need to understand machine coordinates, homed / referenced machine, work offsets,
and G90  & G91. G53 works in machine coordinates and G28 works inclusive of work offsets
and distance mode (ie G90 / G91). So defined controller configuration has an affect
on what happens when using G28. May also want to have a look at G30 and G55 commands.

Home can also be the same as Machine zero.

So if one does not understand some of the cnc basics and uses commands ( G53, G28, G30,
G5x, G0, G1) to move the axis...... the axis may not go where the user thought it would.

Note: The controller only knows what it is told and that includes current configuration
      and implements commands as instructed.

So it can be confusing if the basics and the big picture of setup is not understood.

A few command examples:

G53 X0 Y0 Z0 -  Makes a straight traverse run to Machine Zero

G30 - Makes a straight traverse move to machine zero

G28 - G28 without defined axis all axis goes home in the order of Z then all the rest.
 USED with a defined axis ONLY the defined axis goes home via the intermediate point.
 In g28 you can call a single axis to home, in G30 ALL axis go home reguardless and G28/30 in MACH3 is backwards to FANUC.

G0 & G1 used relative to PART
 
G55 G0 Z0 X0 Y0 - Changes  the Fixture / work offset then goes to X0 Y0 Z0 as straight traverse move at rapid speed

When you ask........
  
Can anyone tell me why my Mach3, G53 & G28 are doing the same thing.

I now ask you......
Under what conditions and how G commmand is coded will they work the same?

RICH
Title: Re: G53 & G28
Post by: kharrisonkevin on April 10, 2016, 08:55:08 AM
Thanks Rich, it's all new to me. 1 of me home switch wires broke so I disabled them. What I was doing with the original gcode run was just milling my bed top flat. I had run the codes several times with no problems. On my very last run at the end of the program instead of the cutter coming up .100 it started to cut down into the table. This was for no reason as my gcode was telling it to come up +1.00. And I had noticed throughout the entire x movement  every 3rd x dro was a litter off in the minus for no reason as the x was only traveling in the + so backlash should not have be a issue. What are your thoughts.
Cheers Kevin
Title: Re: G53 & G28
Post by: kharrisonkevin on April 10, 2016, 08:59:59 AM
What I am trying to say is I can run the program 6 or 7 times it works fine but when I run it again it doesn't
Title: Re: G53 & G28
Post by: ger21 on April 10, 2016, 09:35:54 AM
Quote
n my very last run at the end of the program instead of the cutter coming up .100 it started to cut down into the table. This was for no reason as my gcode was telling it to come up +1.00.

What did the DRO show?
If the DRO showed it moving up, then it's probably an electrical issue.

Quote
And I had noticed throughout the entire x movement  every 3rd x dro was a litter off in the minus for no reason as the x was only traveling in the + so backlash should not have be a issue.

I don't understand what you're saying here?
Title: Re: G53 & G28
Post by: kharrisonkevin on April 10, 2016, 09:38:15 AM
Why does the same gcode run good for me for 6 or 7 times but no for the next time I run it
Title: Re: G53 & G28
Post by: ger21 on April 10, 2016, 09:41:36 AM
The part I quoted is what I don't understand.
You have to explain exactly what is different to try to find an answer.
And I already answered that part of your question.
Title: Re: G53 & G28
Post by: kharrisonkevin on April 10, 2016, 10:04:38 AM
Hi Gerry. The dro was showing correctly in all the y movements. About 1 out of 4 x axis movements in the + direction were short about .0025. The z axis was correct.  Kevin
Title: Re: G53 & G28
Post by: kharrisonkevin on April 10, 2016, 10:28:51 AM
What I am saying is : the coman's are: z - .001 y63 x1.125. It moves to z-001 y63 ok but x only moves 1.1245 approx.. why does it not go to the proper dro because the x axis is only moving in 1 direction so if there is any backlash it shouldn't be a issue. 1 out of 4 x moves are rite.  All the x moves are in the +direction.
Title: Re: G53 & G28
Post by: ger21 on April 10, 2016, 10:37:10 AM
Backlash does not display in the DRO. The DRO is the commanded position, not the actual position. Most likely, what you're seeing is that the display is rounded off, due to your steps/unit settings.
Title: Re: G53 & G28
Post by: kharrisonkevin on April 10, 2016, 11:03:15 AM
So you are saying that my x axis mite not be set too 100%.I set all my calibrated all my axis with a 18 inch Mike and as close as I could get was what I thought was perfect according to the Mike. As for backlash I have to set that. After setting up everything is I go into config go to save will that save all my settings
Title: Re: G53 & G28
Post by: mc on April 10, 2016, 03:55:03 PM
Mach will move to the nearest step it's capable of, and that is what will be displayed in the DRO.
For example, say you have a step resolution that works out at 0.3mm (very crude, but it's only an example), and you command a move of 1mm, the nearest position Mach can command is 0.9mm. Although you command 1mm, Mach is intelligent enough to know it can't command that exact position, so it rounds to the nearest position it's capable of.

As for your Z problem, if your DRO is showing the axis moving in the correct direction and the machine is physically not, you have either a Mach configuration issue, or an electrical/mechanical fault. If the DRO isn't showing the move in the correct direction, then there is an issue with your g-code. As Rich said, the controller i.e. Mach, only does what you tell it to.
Title: Re: G53 & G28
Post by: kharrisonkevin on April 10, 2016, 04:13:27 PM
Now that is in plain English I totally understand.  Thanks for spelling it out. I'm new to the cnc world so it is a lot more complex than I first thought.  Thanks you have a good 1 Kevin.
Title: Re: G53 & G28
Post by: kharrisonkevin on April 11, 2016, 04:48:38 PM
Got it going good set up the backlash just got to fix the home switches thank to everyone for the help