Getting started with Linux, LinuxCNC and CNC

Hm, two more questions.
I ll try my best to explain what happens - in several occasions, I have loaded the desired tool (for instance T1) touched off the part for x and z, loaded the desired ngc file, press play and... the coordinates change - what I have set 30 seconds ago as lets say x10 z10 on DRO is now x-45z-128. Darn. Its not a problem if I work on one piece, but it is a problem when it happens when I m in a middle of the run, so I have to re-position everything. Or if (as it did) the carriage hits the tailstock supporting the work piece. What can cause it, and how to cure it?

Second question (I might have asked before) is for subroutines, the taper OD one. Its all good when you work right to left, from smaller od to larger - to chamfer the edge for instance. But what if I need it to do the opposite - working from right to left, normal right hand tool, to cut from larger od to smaller od? Is it possible, or does one have to work a separate subroutine for it?
Thanks fellas

But what if I need it to do the opposite - working from right to left, normal right hand tool, to cut from larger od to smaller od? Is it possible, or does one have to work a separate subroutine for it?

In most cases you will need to create or edit an existing subroutine such as one of the OD taper subs to change the direction of cut.
Often the authors will have error checking built into the sub to keep it from making unwanted moves.
If you have a sub that you wish to use in a different way / direction than it was designed after studying it you may find it is straight forward to edit it to a new sub for your desired outcome.

Rick G

I canceled all offsets several times, but still, sometimes it does that. Its measured in in G54 coordinate system, I m running the same code making some part after part, but from time to time it "looses" it, and when I re-start the cycle, the coordinate system goes nuts and change the values. If I m lucky enough, I can stop the cycle, go to MDI, call the correct tool (that was actually used in that time) and everything gets back to normal - the coordinates I mean. Once I wasnt so lucky, the tool hit the chuck (the tailstock hitting isnt as bad...).

Another question - havent found the answer or similar topic - how can I change the machine zero position? I understood that it cant be done through g code, so I presume I would have to change some value in a specific file - why I want to do it - I had to make some hardware fixing, and now machine zero is out of the travel range of the machine, so if I try to go to machine zero my steppers stall on their maximum travel range on the fixture. So I would like to position the cross slide on the middle of the travel on both x and z axis, and to keep that position as machine zero for future reference.
Thanks



edit, reading some more right now, it seems that homing (on a machine that doesnt have homing switches) set the G53 to zero? is that correct?

With the touch off (work coordinates),
or G10 L2 Pn or G10 L20 Pn.

G53 is for making moves in the machine coordinate system (no offset), So for example that G0 G53 X0 Y0 Z0 will move the machine back to the home position.

Thank you, if I issue that command (G0 G53 X0 Z0) my lathe tries to go off the hardware capabilities of the machine. I had it dismantled recently due to repair, and the previous configuration and zero are not correct anymore. But after I asked a question, I bumped to a possible solution for me - since I dont have homing switches, I should move the x and z to desired point, do the homing sequence, and then that should be machine zero point for further reference. I shall try this in the morning when I get to shop

G53 does actually send the machine to home position (the position I choose as home), and I am glad its solved

thanks!