Mini lathe conversion to CNC

Andy,
I added in that line but when I try to start up LinuxCNC again it gave me an error saying that it was already linked to something.

After a little searching I found this thread for a HAL example for external E-stop: forum.linuxcnc.org/forum/47-hal-examples/25861-external-e-stop

It uses the ESTOP_LATCH component and I just changed the last line to match the mesa hardware and it seems to be working now. The Axis screen now shows the X button depressed when I push the switch and stepper motor also stops counting.

Can someone help me understand the relationship between the home position (X and Z after the home all button is clicked) and the X0 and Z0 coordinates? For example on a lathe setup X0 is located at the centerline of the starting stock and Z0 is located at the end of the stock sticking out from the lathe chuck. In this case, is the home position and X0 and Z0 the same or how should it be set up to be useful for running a CNC lathe program?

Ok, follow up question: let's forget about the work coordinates for a moment. If I want to, could I write my cnc program moves based on the machine's limit switch/zero position coordinates? This might be a dumb idea, but I want to hear what others think ... I imagine it's an odd thing to do in a lathe but maybe more common in a milling machine?

TML:

I am a novice, but let me try to explain my reasoning. It might help.

You could program from the home being X=0 and Z=0 (or X=Y=Z=0 for mill). However, the numbers have no relation to the part. I like to set X=Z=0 on the part. Then if I jog or use MDI the numbers used relate directly to the part.

You could program using X=0 and Z=0 at references on the part as home. However, if you move to machine X=Z=0 you end up at the part, or with X possibly inside the part. I use machine home for tool changes so this would cause trouble.

So, it keeps me straight to place home with X furthest towards me and Z furthest towards the tail stock. This is then the tool change position. Then set work coordinates with X=0 at the center of rotation, and Z=0 at end of part. Set these work coordinates to match your CAD drawing so the numbers displayed have a real meaning.

I do the same with my mill for similar reasons.

This all matches what Andy said.

Does this make sense?

Hugh

Andy, I think my set up is pretty similar. It probably will be easier for me to learn what's wrong with my process if I just show you what I have so far. And most of what I've learned so far is just from reading and self taught that might need some corrections from those with practical hands on experience that I'm lacking. To start out, attached is a drawing I made to shows where things like home/limit switches are located.

First thing I do is click home all. The machine's homing sequence is like this: the cross slide goes toward X+ until it trigger the X home/limit switch and establish X zero, then moves back towards X- a distance of 7.230 mm (programmed X home position). Machine then moves towards Z+ until it trigger the Z home/limit switch and establish Z zero, then moves back towards Z- a distance of 5.000 mm (programmed Z home position). Screen then displays the coordinates X-7.230 and Z-5.0000.

What I just want to do right now is a simple turning operation on a long piece of stock. One end is supported by a live center from the tail stock. I simply want to make a light cut with a depth of cut of 0.2 mm and length of cut 28 mm. The stock is small diameter (5 mm) to be turned down to 4.6 mm. Distance from the tool's cutting edge to center of the stock is 5.475 mm. So I go into tool table and put -5.475 for X offset. Please let me know if this is right or wrong.

Now for the CNC program to do this turning task, this is my first attempt from looking at some samples:

G8 G90.1 G21 G18
G94
M3
G43
G0 X2.75
G1 X2.3 F60
G1 Z-28
G0 X0 Z0
M5
M2
%

Basically I want the machine to just rapid the tool straight towards the stock then steadily bring it in more just enough for a light 0.2 mm deep cut. Then have the slide move towards Z- a distance of 28 mm to reduce diameter of that section from 5 mm to 4.6 mm. Then finally bring the tool back to original home position (X-7.230 Z-5.000). Does this look Ok?