My Mill or Their Code?

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21 Aug 2022 06:10 #250143 by Bumbino
Hello All,
            I asked a related question a year ago and we got it resolved, but i'd like to know what's actually going on.
            
            Full disclosure I know what G54 is - that's it. With that being said my cnc mill is running great and i'm happy with the success. O'kay, so i'm using fusion 360 and in my post nc files using grbl as the processor i'm getting the following lines
            
            at top (about ten lines down)
            G28 G91 Z0
            G90
            
            at bottom (two tool lines follow before end)
            G28 G91 Z0
            G90
            G28 G91 X0 Y0
            G90
            
            So when these lines run they drive my endmill into the table. Deep. At the beginning it drags through the work to the desired start point, raises and begins the ramp or zigzag descent. It's brutal. So i try to remember to remove this from every file and then most times do a "simulation" in linuxcnc by just not powering on the steppers.
            
            ...anyways... What can I do about this? Is there some machine setup that i missed? I figure if fusion 360 is placing these lines in everyone else's files it must be normal. So what can I do to make my machine do something desirable when these lines are present?
            
            Thank you,
            John

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21 Aug 2022 06:38 #250144 by Henk
Replied by Henk on topic My Mill or Their Code?
G28 is a pre defined position. Jog your machine to a safe position above the table and enter g28.1 mdi command. This will store that position as the g28 position.

Read the gcode documentation.

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21 Aug 2022 07:05 - 21 Aug 2022 07:19 #250145 by Bumbino
Replied by Bumbino on topic My Mill or Their Code?
Hey Henk,
Thank you! Will this be stored permanently or will it reset when i shut down? edit* it looks like it might be stored. The G28 position is stored with G28.1.*

I have tried reading the documentation. I've always had trouble learning by reading certain things. It just becomes overwhelming and nothing at all sinks in. I hate it.

Thanks again,
John
Last edit: 21 Aug 2022 07:19 by Bumbino.

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21 Aug 2022 20:58 #250159 by rodw
Replied by rodw on topic My Mill or Their Code?
It might be F360 has a different view to you. It assumes that Z0 is at the top of travel and downward travel is negative.
So G28 G91 Z0 should move to the top of the Z axis (without a G28.1)
Linuxcnc stores all variable data like your G28 setting in a file ending in .var in your config folder between sessions

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21 Aug 2022 21:25 - 21 Aug 2022 21:36 #250162 by JPL
Replied by JPL on topic My Mill or Their Code?
If I remember correctly it is also possible to use G53 instead of G28. Have a look at the post process screen and I believe you should have the option of G53 or G28 for 'Safe Retracts' (G28 is the default). Then with G53 it should also be possible to set the x y z home position directly within the same screen (just above safe retracts). (<-This is only for turning posts)

Note that this also depends of which version of the post processor you have. I'm sure that v43654 and up have it, while 42049 does not.

Post processor are here: cam.autodesk.com/hsmposts


 
Last edit: 21 Aug 2022 21:36 by JPL. Reason: corrected info, added link

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21 Aug 2022 21:43 #250163 by JPL
Replied by JPL on topic My Mill or Their Code?
Ohhh   I see that you mentioned that you're using the grbl post processor. I'm not sure you have the same options (G28 or G53) with that...

Why not using the post processor developed specifically for linuxcnc instead?

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21 Aug 2022 21:56 #250164 by tommylight
Replied by tommylight on topic My Mill or Their Code?
G28 is used for homing on 3D printers, not sure what GRBL uses it for.

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21 Aug 2022 22:12 #250167 by Bumbino
Replied by Bumbino on topic My Mill or Their Code?
I found about a year ago that I was supposed to use grbl/grbl processor for linuxcnc. I also found that again recently as i had forgotten. What processor should i be using? 3 axis cnc mill.

Thanks,
John

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21 Aug 2022 22:55 #250170 by JPL
Replied by JPL on topic My Mill or Their Code?

I found about a year ago that I was supposed to use grbl/grbl processor for linuxcnc. I also found that again recently as i had forgotten. What processor should i be using? 3 axis cnc mill.

Thanks,
John
 


Well, I guess you can use whatever suits your machine BUT I don't see any reason why the Autodesk HSM post for Linuxcnc mill would not work with Linuxcnc mill. Then I've also checked that the latest version of grbl post also allow you to choose G53 or G28.  

My suggestion would be to first try selecting G53 with your current grbl post processor and see if that correct the problem the way you want your machine to work. If not then it is just a matter of downloading the LinuxCnc post, install it and select it when you process it. You can this way easily switch posts to compare the file generated by both.

The other thing is that you must also have the minimum required 'post engine version'.for a given post. This is not a problem if you have the latest Fusion 360 (2023) but if not fusion may fail when processing the files. Have a look here: forums.autodesk.com/t5/hsm-post-processo...update/td-p/10182498  Not linuxCnc but related same way.

 

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21 Aug 2022 23:13 #250171 by JPL
Replied by JPL on topic My Mill or Their Code?
Good writing about G28 vs G53: www.mmsonline.com/articles/g28-versus-g53
 

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