Homing to sides of workpiece with real tool How? Lathe

Hello all,
Another day spent and I can say 100% for sure that this does not work as intend and described. It is in my so bad that is is unusable as it ruins workpieces.

The problem is repeatable but I have no solution.
I use a feeler gauge to keep the tool 0.1mm away from the workpiece. I thus home the X and Z axis respectively.

I then use "Tool touch" off as described by OT-CNC and others and enter X 0.1 and Z 0.1`.

At this point, "it" enters X 0.1 and Z -0.1 into the tool table for the tool used.
NOTE that one is + and on is - although I entered (+) 0,1 for both touch offs values.

Now if I do it all again (for theoretically another workpiece), and use the same "Tool touch off" entering (+) 0.1into both Z and Z, it enters 0.233 into X and -0.1 into the Z of the tool table.
That makes not sense.

The tool then crashed into the workpiece on G00 X0

Here is the worst part:
I then revert the tool table by editing it and deleting the X and Z values it entered.

It makes no difference. The tool will now ALWAYS be off by some amount.
I have deleted the tool table,
Created a new one, (yes, I reload the tool table every time)
Re-started Linus CNC
Re-booted the PC

None of it makes any difference. When I hoe the axis, the previously accumulated tool touch offset is still present and it is impossible to get the X and Z to show 0 after homing.

I have no idea where it stores these values but it is definitely not in the loaded tool table.


The only way to get it undone is to see what it shows after homing for Z and Z and enter the opposite values into tool touch off.
Thereafter, the tool table has to be cleaned again.

Surely other folks have come across this issue? It has unfortunately ruined my workpiece when I ran it the second time round.

Regards
Bernt

I'm sorry you are still having trouble with this. If your part zero is the front of the stock, you should be able to face it then enter Z0 for that loaded tool in G54. Your program also has to reflect G54 with Z0 from the faced stock. Your program should have a positive Z retract position to start so you don't crash into the stock. I always do a dry run either with Z0 away from the part or remove the material from the chuck to prove out the program. Sometime I run it in plastic first if I'm not 100% confident. What are you using to generate the G code?

I use a feeler gauge to keep the tool 0.1mm away from the workpiece. I thus home the X and Z axis respectively.

I think you are still confusing homing with part zero or work offset (G54). Homing is done so the machine knows where it's 0,0 is when you 1st power up. I assume you don't have home switches on your machine? If so I would add them and configure your ini to reflect the overall travel so linuxcnc knows the soft limits of travel. This way when you power up, the machine always homes to the same place and establishes it's reference. It sound to me you always have a different home when referencing to your stock? You need a repeatable reference which are home switches.

OT-CNC wrote:

I'm sorry you are still having trouble with this. If your part zero is the front of the stock, you should be able to face it then enter Z0 for that loaded tool in G54. Your program also has to reflect G54 with Z0 from the faced stock. Your program should have a positive Z retract position to start so you don't crash into the stock. I always do a dry run either with Z0 away from the part or remove the material from the chuck to prove out the program. Sometime I run it in plastic first if I'm not 100% confident. What are you using to generate the G code?

I use a feeler gauge to keep the tool 0.1mm away from the workpiece. I thus home the X and Z axis respectively.

I think you are still confusing homing with part zero or work offset (G54). Homing is done so the machine knows where it's 0,0 is when you 1st power up. I assume you don't have home switches on your machine? If so I would add them and configure your ini to reflect the overall travel so linuxcnc knows the soft limits of travel. This way when you power up, the machine always homes to the same place and establishes it's reference. It sound to me you always have a different home when referencing to your stock? You need a repeatable reference which are home switches.

Maybe I am confusing something but even then, I should get repeatable results.
My machine does not have switches and most machines apparently do not and I also can't see a reason for them.

Let me start from the beginning.
1) My G-code has it's reference at the front right corner of the workpiece final size.
2) My chucked workpiece is the final size for OD and Z for this experiment
3) I start up
4) I move to the right, clear of the workpiece.with my tool in the toolpost.
5) I move in and then slowly to the left with a 0.1 feeler gauge on the workpiece face.
6) When the tool reaches the feeler gauge, I home the Z axis.
7) I move the tool out and to the left so I can move towards the OD, again with a feeler gauge.
8) When reached, I zero the X axis.
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)
10) I move the machine 0,0. (That worked before in putting it front right of the workpiece but now recently it will crash into the workpiece for unknown reasons)

Next, I now load the file.
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.

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.

During this process, my tool table changed by itself to have the entry of Z -0.1 and Z 0.1.

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

The tool table with change by itself then to have something like X-0.22331 and Z+0.1.

I am not able to get the homing done nor can I get the tool to end up at the correct 0,0 place.
If I repeat the whole lot again, the tool table will change to have X-0.33?? and Z 0.1.

Whatever I do, it never works as expected again and that is currently where it sits. When I restart, and click home X, it now shows 0.40 and for Z it shows 0.

Deleting the obscure accumulating values from the tool table do not seem to make any difference.

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.
8) 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?

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