Resolved: Homing - Quick question...

Nightowl · 28 Apr 2022, 17:43

Thanks, @fcwilt, but just so I'm clear, all I need do is change the X value to a positive number if I want to use the proximity sensor on the right, rather than the left?

I also see your comment about the two homing speeds. The RepRap Config Tool does include these, but the maximum speed of my stepper motors is 2500, so 6000 seemed a lot!

fcwilt · 28 Apr 2022, 17:58

@nightowl999 said in Homing - Quick question...:

Thanks, @fcwilt, but just so I'm clear, all I need do is change the X value to a positive number if I want to use the proximity sensor on the right, rather than the left?

The sign of each X move would change, the G1 H1 move would become a positive number but the G1 back-off move would become a negative number.

Of course you have to wire in the new sensor and configure it correctly as the X endstop.

I also see your comment about the two homing speeds. The RepRap Config Tool does include these, but the maximum speed of my stepper motors is 2500, so 6000 seemed a lot!

The speeds are up to you. For example you could use F2500 and F250 as your fast and slow speeds. It's not really essential. The assumption is that the second, slower move will result in greater accuracy of the homed position. Does it really do that? I don't know. I do both fast and slow just to be safe.

Frederick

Nightowl · 28 Apr 2022, 18:26

Thank you @fcwilt.

fcwilt · 28 Apr 2022, 18:55

@nightowl999 said in Homing - Quick question...:

Thank you @fcwilt.

Always glad to be of help when I can.

Frederick

Nightowl · 8 May 2022, 16:18

When I home my Duet-controlled KillerBee CNC machine to the rear, right, up, the machine position is shown in DWC as X=-3, Y=784 and Z=97, all of which are 3mm off the proximity sensors. This isn't logical to me (except for X).
What I would like to see is X=-3, Y=-3 and Z=-3, i.e. 3mm off their respective 0's.
Is this something I can adjust in my config.g file or their respective homing files, please?
Thanks

fcwilt · 8 May 2022, 17:45

@nightowl999 said in Homing - Quick question...:

When I home my Duet-controlled KillerBee CNC machine to the rear, right, up, the machine position is shown in DWC as X=-3, Y=784 and Z=97, all of which are 3mm off the proximity sensors. This isn't logical to me (except for X).
What I would like to see is X=-3, Y=-3 and Z=-3, i.e. 3mm off their respective 0's.
Is this something I can adjust in my config.g file or their respective homing files, please?
Thanks

Is it normal for CNC machines to have the XY origin (0, 0) at the right rear as opposed to FDM printers where it is usually left front?

So on a CNC machine is the left front position XY two negative values?

Thanks.

Frederick

Nightowl · 8 May 2022, 18:33

As I understand it, @fcwilt, machine 'home' can be either rear, right, up or front. left, up - as they're essentially the same (as it was explained to me).

The reason CNC machines use right, rear, up is to ensure the working area is clear of sharp, jaggy things when fixing stock, etc. I don't know anything about 3D printers, though.

My old Shapeoko had it's machine home at right, rear, up and that made sense to me. Project 'home' is slightly different, in that it's the starting point for cutting the stock (wood, metal, plastic, etc) which is mounted on a spoil board. Normally (but not exclusively) the front left hand corner coordinates of the stock is X=0, Y=0 and Z being measured from the top of the stock, so all Z cuts are down. some people prefer to set Z0 on the waste board, though.

Does that help?

fcwilt · 8 May 2022, 21:27

@nightowl999 said in Homing - Quick question...:

As I understand it, @fcwilt, machine 'home' can be either rear, right, up or front. left, up - as they're essentially the same (as it was explained to me).

The reason CNC machines use right, rear, up is to ensure the working area is clear of sharp, jaggy things when fixing stock, etc. I don't know anything about 3D printers, though.

My old Shapeoko had it's machine home at right, rear, up and that made sense to me. Project 'home' is slightly different, in that it's the starting point for cutting the stock (wood, metal, plastic, etc) which is mounted on a spoil board. Normally (but not exclusively) the front left hand corner coordinates of the stock is X=0, Y=0 and Z being measured from the top of the stock, so all Z cuts are down. some people prefer to set Z0 on the waste board, though.

Does that help?

Thanks.

I think the confusion is from the terms "home" and "homing".

To me in the FDM printer world "homing" is the process of "synchronizing" the logical position of each axis (where the controller "thinks" things are) to the physical position of each axis (where things actually are).

Homing can be done to either the min or max end of an axis. And there is no requirement that all axes home to the same end, min or max.

The "origin" (0, 0) has no fixed relationship to the position used for homing. The origin is often the left, front but I use the center of the bed.

I generally mount the endstop sensors to the rear of the printer. This means that Y would home to the max end. X would home to either the min or max end depending on where it was easiest to mount the endstop sensor.

When a print is finished I position the extruder out of the way. Typically to X=0, Y=max which on my printers is the rear center of the bed. I call this the "parked" position to distinguish it from the "origin" or the "home" position.

So where do wish 0,0 to be? The left front or the right rear?

Frederick

Nightowl · 9 May 2022, 16:44

@fcwilt OK, but to me, homing is the process by which the machine understands where everything is. This is particularly relevant where the settings aren't stored in an EEPROM and retained, but configured during startup.

And there does seem a significant difference between CNC and 3D printing in that respect, too!

fcwilt · 9 May 2022, 16:48

@nightowl999 said in Homing - Quick question...:

@fcwilt OK, but to me, homing is the process by which the machine understands where everything is. This is particularly relevant where the settings aren't stored in an EEPROM and retained, but configured during startup.

Isn't that what I said?

To me in the FDM printer world "homing" is the process of "synchronizing" the logical position of each axis (where the controller "thinks" things are) to the physical position of each axis (where things actually are).

Frederick

Nightowl · 9 May 2022, 16:52

You did, sorry @fcwilt. I'm switching between two threads and trying to cook my dinner!!

I would like the 0,0 to be right rear, in answer to your question (which I also missed )

Printers do have a Z height too, don't they? My knowledge of 3D printing is non-existent, in case you were wondering!

Phaedrux · 10 May 2022, 00:33

Right rear 0,0 position is fine. It's the typical right hand coordinate system just rotated 180 degrees. The problem occurs when you only rotate it 90 degrees in which case you'll get a mirrored axis.

The physical endstop position is defined in the M574 command. If you want the homed position to be 0,0 set it to 1 for the low end of travel.

The homing moves in your macros will need to be negative to move towards the endstop.

Now it's up to you to define the motor rotation direction such that a negative move goes in the rear/right direction.

Nightowl · 10 May 2022, 10:34

Thank you, @phaedrux