Probem with soft limits mach3 turn

I recently bought a small Boxford CNC lathe which has been converted to run Mach3 Turn.

My problem is the setting of the soft limits within mach.

I set the soft limits X soft min -100 mm X soft max 0

Z soft min -130 mm Z soft max 0

I saved the settings. After switching on the home limits i get an error message.

Machine out of limits for soft limit activation.

This is despite both axis been homed and the work offsets zeroed.

(Machine homes in a positive direction as it should)

Any advice would be appreciated.

John

My guess is that your posistin is outside the limit. I also think soft limits are im machine coordinates. Try to show the machine coordinate at your posision (machine cordinates are always in radius).

Best regards

Anders B

PS Oh yes, machine coordinates are unaffected by work offset. DS

Edited By Anders Be on 01/04/2021 20:23:25

Hi John,

Homing and soft limits can be a bit of a minefield. My approach is as follows - hopefully there may be something here to help with your problem. Note the numbers here are for my Super 7, yours would probably be less for a smaller lathe.

• I don't have home/limit switches on the Z axis as they serve no useful purpose IMHO. They would have to be in positions where they would allow free movement of the carriage whatever the position of the tailstock and whatever chuck you have fitted, so by the time they are activated it's probably too late. Z axis homing is not enabled. Anyway using stepper if you hit an endstop it just stalls the motor - unlikely to break anything, though you do lose any referencing.
• I do have an X home switch which allows the X axis to be referenced at its minimum position, closest to axis. This is used so all the tools can be referenced for turning diameters. I described this somewhere on here. X axis homing is enabled.
• Soft limits are set, but the only one I rely on at all is to stop the X axis running off the ballnut. The numbers I use are Z: +250mm / -250mm; X +110mm / -20mm
• The homing procedure is, on switch on:
  • Make sure you are in Diameter Mode
  • Select Machine Coords
  • Move X axis to nearly zero position
  • Click Set Home X button on manual screen - X axis slowly moves in until home position detected (but usually the DRO is not zero)
  • Click Zero World X - this sets the machine X DRO and coordinate to 0.000
  • This is all done with the carriage in about the middle of the bed - as I have an ordinary leadscrew and half nuts this is done with the rack feed, then I engage the halfnuts and they stay closed.
  • Click Zero World Z - this sets the machine Z coord to 0.000.
• Now all Z movements are made by jogging, not the rack handwheel. There is no manual wheel on X anyway. There's a temptation, when you finish a bit of machining with the tool near the chuck, to release the half nuts and wind the carriage back - this loses the Z reference and if I'm not careful to reset it after a while and doing this a few times the machine thinks that the Z machine coordinate has got too big (negatively) and it will hit the soft limit. I'm learning to only use jogging.

All this is done in machine coordinates. When I select programme coordinates and a tool then the X DRO shows the actual turning diameter provided the tool offsets are set up. Work offsets and tool offsets do not affect machine coordinates. For one-off work, work offsets are irrelevant I think. The above procedure allows me to turn to a diameter relatively accurately without having to touch off the tool to the material. For the Z axis I have a tool touch sensor and a macro that will find the end of the material in the chuck, zero the X pgm coord, and move the tool 20mm to the right.

I hope this helps, ask away if anything not clear.

Thanks for your replies.

It appears that soft limits only work in Mach turn when radius mode is set. There is no reference to this in the manual.

I found a commit on the mach3 forum to that effect. When I tried it in radius mode it worked.

I wish to stay in Dia mode so will have to do without soft limits on my lathe.

John

I use a clamp on limit switch for negative Z axis moves. The option of using collets or a chuck makes a fixed one problematic as mentioned by John. I use this for homing/limits once the setup is done so that any error or overnight shutdown can be recovered from with minimal effort. You could easily mount fixed ones on the X axis and moveable ones on the z axis and then not worry about soft limits, just need to remember to set them up after things like chuck changes.

Martin C

Well I just checked on my lathe which is in diameter mode and soft limits work on both X and z axes exactly as expected. This may be version dependent, I am using R3.043.062 which I believe is the latest recommended for Turn as it supports threading correctly.

Edited By John Haine on 03/04/2021 10:22:33

And looking again at your first post, note that your zero home position is at a soft limit. You need to make sure that the soft limit range brackets the machine coordinate zeros.