Homing to sides of workpiece with real tool How? Lathe

I wrote 2 days worth of gcode for my lathe.

Tool is 3mm half round and cuts both sides and on the round front.

The code was written to use cutter compensation for 3mm diameter.
It works.

So PROBLEM:
How do I home the axis with the tool in place?

Code is designed for 0,0 to be at right front corner of the workpiece but without compensation so centre of my tool must be at that corner.

How do I work around this hurdle?
Add offsets in the code everywhere?
Is there an easier way at all?

Any help is greatly appreciated.

Regards
Bernt

think there is a couple of solutions, you will need to pick the one that fits

so machine home is the location of the machine home, where the 0 is on each physical axes. this let the machine know where the limits are. then there a work spaces this let you move where 0 is in relation to your program, then there is tool comp this defines where the tool is after you turn it on.

the machine should be homed before you load your parts there should be a switch that it "home" to every time you turn the software off, if the machine crashes, or you other wise lose your position.

then you need to touch off, i use a fixed point like a corner or a probe.
this moves the G-codes work space the actual numbers you wrote.

now you can touch off your tool, this will give you the length in relation to the work space zero. when you call a tool then do a cutter comp turn on move it will adjust for the tool length and you will get the right cut. if you don't shutoff or crash the machine, you can put the next part in and touch off and go.

I think I understand that.

However what I do not understand yet is that when I touch off with the real tool loaded, then surely I will be off by half the tool diameter still?

How do I compensate for that?

it can be if you use the same tool that your cutting with and you touch off with it before turning on cutter comp then the work space may be off by half the diameter. if you have a 3mm center i would use that. when you use touch off it will also allow you to put in a number this is the distance from the edge you touch to 0.

example
you have a 3mm half round shaper tool in your tool post, you bring the side in and touch the end of the stock with the side of the round in the Z axis, and touch off with 0. you would be off by 1.5mm if you design you program to cut with the center of the tool and 3mm if you had back cuts in you program. so you put 1.5mm in the box when you touch off this tells the machine you have 1.5mm to the end(zero) of the work. now you come in with the front of the tool and touch it in the box you want to put 1.5mm + radius of the part this sets the center of the stock. in the tool table you you set you diameter for your cutter comp, and the length. when you cut with cutter comp you may find your +1.5mm on the radius. if that is the case you touch off again with out the 1.5mm. if you change tools you want to use touch tool to set the length this should set it to the different between the touch off (0,0) and the tool touch off.

this is how it seem to work for me on a Mill so i have filled in how i believe it works on a lathe, i would run some test on your equipment.

Ahaaa.

So there is a box where I can enter the difference!!.
I did not know that.
It makes sense and would certainly sort out the problem.
Will try it tonight.!

I cannot get it to work.
I tried for several hours.

I find the touch off unpredictable.
I do use G54.
The tool touch off also works in ways I do not comprehend. It wants 1 value but shifts the tool both ways but not equal WHAAAT?

Entering offsets into the tool table seems fruitless too.

Attached is a picture of what I want to do and where my 0.0 needs to be relative to the tool.

Can anyone shed light on this mystery?

Regards
Bernt

How about posting a screen shot also which boxes are you entering the data in?

The home position can be anyware you like it does not have to be at the edge of the stock and I believe that is G53. Then when you touch off it become generally G54

which version of Lcnc are you using


linuxcnc.org/docs/2.7/html/lathe/lathe-user.html

How I do it.

Home the machine - as I have no home switches I generally move the x axis z axis to mid travel and home there. (with x being approx=0 = the spindle axis)

Mount the tool you wish to use.
Using the MDI window, enable that tool with a Tx M6 where x is the tool number.

Take a small test cut by manually jogging the machine in x to get a small cut and then jogging in Z, Jog back out in z leaving x unchanged and measure the resulting diameter

touch off the x axis (not tool touch off) and in the input box enter half the measured diameter (assuming you are in radius mode rather than diameter mode)

The on screen coordinates for radius/diameter should now reflect the measured diameter too as a check.

Having tool offsets in the tool table is only of value if you can change tools with the new tool being loaded in a known location - eg by using a quick change tool holder with a separate holder for each tool, or by having some kind of touch off switch that can measure tool offsets on the fly.

Another day of struggle...

I can only use it as follows: Not ideal.
3mm half round tool as earlier.
1) move X in until it touches OD of blank.
2) Home X.
3) remove workpiece.
4) Move X in by 1.5mm on CNC coordinates.
5) Home X again.
6) Workpiece fitted.
7)Move Z left until tool touches face of workpiece.
8) Home Z
9) remove workpieve
10) move Z left 1.50..
12) Home Z again.
Done.

So now the tool centre will sit on 0,0 is on the worpiece corner.
When putting the yool on 0,0, it's centre would align with the worpiece corner. But of course it can't move there as the worpiece is in the way
Surely this must be possible to set with the touch of or offsets somehow?

I have not managed so far.

I assume you have looked over the Lathe documentation. The control point section is helpful.

linuxcnc.org/docs/html/lathe/lathe-user.html

Also, machine home is different from part zero and you are not homing the machine to the part. I think there is some confusion there. Usually machine home is away from the chuck.

You also need to load the tool offset by issuing a G43.

T1 M6
G43