Homing to sides of workpiece with real tool How? Lathe

My machine does not have switches and most machines apparently do not and I also can't see a reason for them.

As explained before, a home switch creates the machine absolute zero. It also sets your soft limits if configured so you don't crash into the mechanical end of travel. When executing code that has a value outside your limits it will prompt you. There are a lot of good reasons to have home and limit switches on a machine.

If you don't want switches you can certainly jog your machine to any position and call it home if you so desire. Be aware you may lose position on the next power cycle if something has moved.

1) My G-code has it's reference at the front right corner of the workpiece final size.

In lathe mode, the center of rotation should be X0. Your G code needs to reflect that.

6) When the tool reaches the feeler gauge, I home the Z axis.

Home could be anywhere on your machine, try most positive Z and X as an example.
Then load tool 1 (M6 T1 G43) jog to your stock with the selected tool and do the touch off for X (enter dia )and Z (face) which should reflect a new origin in g54 for tool1.
Or if you want to use the feeler gage, enter it's thickness. in your case you should be at Z.1

7) I move the tool out and to the left so I can move towards the OD, again with a feeler gauge.
When reached, I zero the X axis

You need to enter the diameter or radius value. X0 is the center of rotation on a lathe.

This should, in my opinion, put the machine 0,0 outside my workpiece in a safe place. (Currently this does not produce a 0,0 on the coordinates. I cannot explain that. I did before)

Your retract position needs to be somewhere safe outside the part.

Next, I now load the file.
9) I enter T2 M6 to load tool 2

Try M6 T2 G43 to load the offset for that tool.


For a test, try programming your tool based on the control point so the tip of the tool reflects the actual diameter. I think you may be further confusing things by programming the center of the tool?

Your points are valid but they should not result in it not working correctly.
Whether I have the lathe centre as 0 or any other point should not make it not operate as expected.
I would think that LinuxCnc does not actually care where my my 0 is on the physical machine. It is just a X/Z motion controller.

The 0,0 I am homing with the feeler gauge is outside and away from workpiece by 0.1 mm and I would consider it a safe origin for this purpose.

I must also mention that for THIS experiment, I use tool orientation 2 with a triangular tool and the diameter set to 0.001mm.
Tools do not seem to work unless there is a diameter specified.

I can say that I have tried all your steps multiple times with various nuances I do not get the same results you describe. I only got them once and they were not repeatable after that.

Has anyone actually tried this tool touch off for a lathe and observed what happens?

What else can I do to convince someone that this is just not doing the right thing?

berntd wrote: Has anyone actually tried this tool touch off for a lathe and observed what happens?

Yes, I use my LinuxCNC lathe almost daily.

What else can I do to convince someone that this is just not doing the right thing?

I think we are all thinking that it is you that isn't doing the right thing, and trying to work out what the difference could be.

Do you have the machine set to "touch off to workpiece" or "touch off to fixture"?

berntd wrote: My machine does not have switches and most machines apparently do not and I also can't see a reason for them.

What makes you think that most machines don't have home switches? I consider them all but essential, especially on a lathe.

4) I move to the right, clear of the workpiece.with my tool in the toolpost.

Which tool? I find it useful to have a "reference tool" which always has zeros in the tool table.

6) When the tool reaches the feeler gauge, I home the Z axis.

You should home to a fixed point on the axis, not to the work. Homing to the work will mean that the G54 offsets will move around.

There are three sets of offsets in play here. When you turn on the machine the step-generators are at zero. Homing sets the offsets added to that position to convert it to absolute machine coordinates. If you switch to viewing absolute coordinates you will see these go to zero when you home. (well, actually, the will go to a position set by the HOME_OFFSET in the INI file)
Then on top of this there is the G54 (G55, G56....) coordinate offset. This converts absolute machine positions to suit you G-code origin.
Then there is the tool table offset, added on when you load a tool and apply the offsets with G43

7) I move the tool out and to the left so I can move towards the OD, again with a feeler gauge.
When reached, I zero the X axis.

I don't know if this matters, but that is unusual. Normally you would set the X to the actual radius (or diameter) of the work + feeler gauge.

This should, in my opinion, put the machine 0,0 outside my workpiece in a safe place. (Currently this does not produce a 0,0 on the coordinates. I cannot explain that. I did before)

Are you viewing the relative or the absolute coordinates?

9) I enter T2 M6 to load tool 2
10) I I click tool touch off for X and enter 0.1 into the box.
11) I click same for Z and also enter 0.1 into the box.

You may also need a G43. With Touchy you need to issue a G43 after a touch-off, it is possible that Axis does it for you, I can't remember.
The various variants of "touch off" do one of the 4 versions of G10. (G10 L1, G10 L10, G10 L2, G10 L20) Which one you get depends on whether you touch off the coordinate system or the tool table, and whether you are set to touch-off to work or to fixture.
linuxcnc.org/docs/2.7/html/gcode/g-code.html#gcode:g10-l1

Now I should be set to go. When I go to 0 on either axis, the tool will touch the workpiece either on the face or the OD.

It all seems to work ok. Until I now restart the whole process.from step 1..

Re-homing with the axes in a different physical position will move _everything_. This means that different tool and G54 offsets will be calculated in the later stages.

I consider them all but essential, especially on a lathe.

Berntd, install home switches right now as these are very much needed in lathe!

You are in very deep waters without switches.

Hi Andy, OT-CNC and group,

Firstly, I really appreciate all your help and patience!

I was 100% sure that it is me doing the wrong thing but after several days (weeks) of experimenting, I am 100% (+/- tolerance) that is it not me.

If anyone has any suggestion or exact steps that they can make me follow, to demonstrate the problem or to conclude that I am indeed the cause, then please shoot. Send me a demo file if you have one and I will follow the exact steps and report the outcome.
I would make a video for 'ya all but I can't hold the camera while operating the machine:-(
Likewise, if anyone has a video that shows the expected results, I would like to see it.


I have previously machined a few parts with this lathe but they were done by not using any touch off as it did not work in the first place..
It started going wrong again after I tried the test / suggestions from OT-CNC posted in #117315 in this thread.

REFERENCE:
If I have a fixed exact OD and length and I want to machine several exact depth grooves into the workpiece, then surely there is nothing wrong with using the right face and OD as the references? I would say that is the best repeatable place.

Touch off:
I do not "touch off to workpiece" or "touch off to fixture" as I could never get that to work as expected. I started this thread because of these issues and they are still the same.
I thus use the "tool touch off" as discussed earlier for example in OT-CNCs reply #117315.

Tool table:
What are your thoughts on the the tool table X and Z values changing but in unpredictable (at least from my side) ways after using tool touch off?

Switches:
I have followed the advice of Joe Martin, founder of Sherline Inc, in that whilst limit/home switches can stop a machine running into its end stops, small machines like my Sherline do not have to have them. In fact, they do not even supply any for the lathe as far as I know. Switches do not prevent workpiece damage or crashing since the path taken to the home position can easily be through the part. Whilst I reckon they are useful, they will not help me solve this here problem.

Regards
Bernt