Just thinking out loud here...



  • Hi,

    The current behavior of a G1 H1... command is to set the current axis position to the min/max value for the associated axis as specified in M208.

    Based on my limited experience the end stop sensors have never been at the min/max position and I resort to G91 G1... and/or G92... commands to set the actual axis position. Some folks change M208 as needed

    Would it make any sense at all to allow, as an option, specifying the axis position to use with G1 H1... in the M574 command?

    Just curious.

    Frederick


  • Moderator

    I dunno, how would that interact with M208 as it is now?

    M208 is the implied result and G92 can explicitly override it at time of use. Seems to cover the bases as is.



  • @Phaedrux said in Just thinking out loud here...:

    I dunno, how would that interact with M208 as it is now?

    M208 is the implied result and G92 can explicitly override it at time of use. Seems to cover the bases as is.

    My thought is that if the optional value appeared in M574 it would be used instead of the value from M208.

    M208 says what the min/max limits and doesn't necessarily match the hardware. M574 deals with the end stop sensors and having the option to include the position of the end stop sensor makes some sense (to me anyway).

    The issue I've seen on occasion is the person sets M208 to establish, say, an X range of 0 to 300.

    But the X end stop sensor triggers outside the bed area at, say, negative 20.

    If you try to use G92 X-20 it doesn't work because it is constrained by M208.

    So then you have to use M564 to allow the G92 X-20 to work.

    Or you have to use G90 G1 X0 to move to a valid position and then use G92 X0.

    In the past it has led to some confusion among newcomers.

    So I was wondering if anticipating those kinds of issues with a modified M574 might make things simpler.

    Not a big deal just got to thinking about it.

    Frederick


  • Moderator

    @fcwilt said in Just thinking out loud here...:

    The issue I've seen on occasion is the person sets M208 to establish, say, an X range of 0 to 300.
    But the X end stop sensor triggers outside the bed area at, say, negative 20.
    If you try to use G92 X-20 it doesn't work because it is constrained by M208.

    Well I would say the correct way would be to use a negative minima in M208 if you wanted to keep the 0,0 position anchored to a position on the bed surface.

    @fcwilt said in Just thinking out loud here...:

    Not a big deal just got to thinking about it.

    I'm definitely not the arbiter of right or wrong or good or best when it comes to RRF. I can only say how I would use it based on how I think it works. @dc42 would have to take a look.

    @fcwilt said in Just thinking out loud here...:

    In the past it has led to some confusion among newcomers.

    Does adding another way to do it make for more or less confusion? 😉



  • @fcwilt I think it might confuse things even more. We already have things like tool offsets and baby stepping which can mean that the position isn't what one might think it is. And if one uses a Z probe, there are another set of offsets that also come into play.

    I can sort of see one scenario where it might be useful but that's a workaround for a firmware limitation in any case. That is to say I can't use a Z probe because my Z motor is connected to an expansion board and that combination isn't supported in RRF3. So instead, I use a switch which is connected to another expansion board. For that to work, I have to set Z min to negative value, do G1 Z-nn H1 then use G92 to set the zero offset. So I guess being able to put that offset in M574 would work but it's just another way of achieving the same thing and would likely add to confusion.


  • administrators

    @fcwilt said in Just thinking out loud here...:

    Hi,

    The current behavior of a G1 H1... command is to set the current axis position to the min/max value for the associated axis as specified in M208.

    Based on my limited experience the end stop sensors have never been at the min/max position and I resort to G91 G1... and/or G92... commands to set the actual axis position. Some folks change M208 as needed

    Would it make any sense at all to allow, as an option, specifying the axis position to use with G1 H1... in the M574 command?

    Just curious.

    Frederick

    Yes I have been considering that. Machines with Z min endstop switches (and no Z probe) would benefit from this.



  • @dc42 said in Just thinking out loud here...:

    Yes I have been considering that. Machines with Z min endstop switches (and no Z probe) would benefit from this.

    One discussion that came to mind as I pondered this was a person who had XY end stop sensors outside the min/max range but wanted to keep M208 to just the valid ranges for printing.

    So the use of G91 G1 moves and G92 was mentioned to him.

    Which of course works and I use it myself - but it has always seemed a bit inelegant - to me.

    It would be somewhat like the trigger height setting for Z probes, only for end stop sensors.

    Frederick


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