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Author Topic: G28.1 with feedrate added into the mix  (Read 2624 times)

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Offline beefy

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G28.1 with feedrate added into the mix
« on: May 08, 2013, 05:18:07 AM »
My cam software for my plasma cutter gives me the following code as part of the touch of sequence:

G28.1  Z15  F500

From safe Z my torch rapids down to 15 mm then travels to the home switch at a reduced feedrate. What I am not sure of is whether it will be using the F500 code or it will be using the % speed setting in Config/Homing Limits. I assumed having the F500 in the line of code would OVERIDE the % setting in Config/Homing Limits.

Someone has told me that in the code above the F500 is redundant because it only comes into play IF there is a G1, G2 or G3 in the line of code. IS THIS TRUE ?? That's my big question.

Googling Mach & G28.1 a description of G28.1 was that it causes a homing move at a % (set in Config/Homing Limits) of the CURRENT feedrate. If that's true then doesn't that mean the homing speed will change depending on what the current feedrate is. I always though the homing % speed setting was a percent of rapid speed and would always be the same.

I'm hoping the F500 command in the line of code will overide the % setting so my homing speed is consistent regardless of the current feedrate.

Cheers,

Keith.

Offline stirling

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Re: G28.1 with feedrate added into the mix
« Reply #1 on: May 08, 2013, 06:58:10 AM »
Keith - on my system (R3.043.022) the behavior of G28.1 is not as described in the gcode reference.

The first phase of G28.1 is at rapid and the second phase is at the % of rapid as set in Homing/Limits
i.e. Feedrate is ignored regardless of whether it precedes or is on the same line as the G28.1.

Ian

Offline beefy

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Re: G28.1 with feedrate added into the mix
« Reply #2 on: May 08, 2013, 02:52:36 PM »
Thanks Ian,

I'll have to write a tiny bit of code to try it on my table.

If that's the case it seems like a pointless exercise to put this referencing speed setting in my post processor, plus homing speed is not constant and is a percentage of current feedrate. Interesting, I would have thought a machines homing speed would be a fixed value, not connected to current feedrate.

Cheers,

Keith.

Offline beefy

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Current feedrate and G28.1
« Reply #3 on: May 09, 2013, 05:25:40 AM »
I think I'm getting to the bottom of the rabbit hole on learning about G28.1

Homing is done at a % of CURRENT FEEDRATE, as set in Config/Homing Limits

When my plasma table Z axis does its very FIRST touch off operation, the only feedrate command that has been given before this is F1 which is 1mm/min in my case. Now I know that my first Z homing operation is not done at a the % setting of 1 mm/min. There are however some G0 command before the first touch off so my question is does a G0 command set the current feedrate to the rapid speed, and therefore my homing speed gets done at a % of the rapid speed.

Or in summary, is the following true:

F1234 in first line of code  -  current feedrate is now 1234 mm/min
G0 in second line of code  -  current feedrate is now machines rapid speed

Cheers,

Keith.

EDIT: Topics merged by Mod
« Last Edit: May 09, 2013, 05:43:29 AM by stirling »

Offline stirling

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Re: G28.1 with feedrate added into the mix
« Reply #4 on: May 09, 2013, 06:24:54 AM »
Hi Keith - Can I ask you to read my first reply again? - It appears you're confusing and interchanging RAPIDs and FEEDRATE moves here and there throughout your last two replies.

Cheers

Ian

Offline beefy

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Re: G28.1 with feedrate added into the mix
« Reply #5 on: May 10, 2013, 05:08:24 PM »
Hi Ian,

yes I was, thanks for the correction.

Cheers,

Keith.