Lathe with stepper motors - limit switch crash

[frijoli]

However, I learned something...if you don't set travel limits, you WILL crash into your limit switches on rapid jog moves. For some reason, it does not "remember" where the limit switch is......

Yes, set your soft limits once motor direction and homing is setup....

Marty, is that correct, or have you seen that to be the case? That the "soft" travel limits will slow down the jog rate.

[martyscncgarage]

However, I learned something...if you don't set travel limits, you WILL crash into your limit switches on rapid jog moves. For some reason, it does not "remember" where the limit switch is......

Yes, set your soft limits once motor direction and homing is setup....

Marty, is that correct, or have you seen that to be the case? That the "soft" travel limits will slow down the jog rate.

From the All in One DC Installation manual, section 6.11:
"Setting software travel limit will automatically decelerate the axis right before it reaches the limit switch, preventing possible
damage to the machine as shown in Figure 6.10.2. Additionally, the CNC11 software will throw an error and stop the machine if a
G code requests the machine to move past the software travel limit."

[frijoli]

Yes, set your soft limits once motor direction and homing is setup....

Marty, is that correct, or have you seen that to be the case? That the "soft" travel limits will slow down the jog rate.

From the All in One DC Installation manual, section 6.11:
"Setting software travel limit will automatically decelerate the axis right before it reaches the limit switch, preventing possible
damage to the machine as shown in Figure 6.10.2. Additionally, the CNC11 software will throw an error and stop the machine if a
G code requests the machine to move past the software travel limit."

Thanks, I assumed this meant during programmed travel, not jogging.
Note to self, "set soft limits".

Clay

[ScotY]

Well, if Clay didn’t know this, my haphazard lazy self doesn’t feel so bad.

The thing is, I would have thought it would know where the limit switch was because it just homed to it, thus there should be no way to crash on a rapid jog. Naturally, if you didn’t set a travel limit, it wouldn’t know where to stop on the other end. My mill was set up with travel limits and it would coast to a nice stop on the switch. It doesn’t make as much sense to set a travel limit on a lathe so I didn’t do it right away. While playing around, I just assumed it would decelerate to a stop when nearing the switch. I assumed incorrectly.

[martyscncgarage]

Well, if Clay didn’t know this, my haphazard lazy self doesn’t feel so bad.

The thing is, I would have thought it would know where the limit switch was because it just homed to it, thus there should be no way to crash on a rapid jog. Naturally, if you didn’t set a travel limit, it wouldn’t know where to stop on the other end. My mill was set up with travel limits and it would coast to a nice stop on the switch. It doesn’t make as much sense to set a travel limit on a lathe so I didn’t do it right away. While playing around, I just assumed it would decelerate to a stop when nearing the switch. I assumed incorrectly.

That is incorrect.
If you have setup your machine correctly when you home the machine, It hits the home/limit switches and backs off of them, THEN sets machine zero. (press Alt-D) If all is setup properly, during normal operation, CNC12 will stop the axis AT machine zero and at the end of its travel(if software limits have been set correctly and yes, you need to setup soft limits in a lathe as well) before hitting the limit switch or hard stop.

What you are describing could be lost steps or misconfiguration. When that happens, the axis are no longer where CNC12 thinks they are. (Open loop system) lost steps can be caused by rapids that are too fast, acceleration to fast for the steppers/machine, taking too aggressive a cut and stalling the motor, binding in the drive system, not picking the correct stepper motors for the machine/control configuratoin, software misconfiguration, are a few examples.

Prove this to yourself, you did a video of your lathe homing to the switches. Once its homed, in slow mode, jog away from the switches a half inch or so and then deliberately come back to them. It should stop right where machine home position was set and not touch the switch.

Report back.
Marty

[ScotY]

Well, if Clay didn’t know this, my haphazard lazy self doesn’t feel so bad.

The thing is, I would have thought it would know where the limit switch was because it just homed to it, thus there should be no way to crash on a rapid jog. Naturally, if you didn’t set a travel limit, it wouldn’t know where to stop on the other end. My mill was set up with travel limits and it would coast to a nice stop on the switch. It doesn’t make as much sense to set a travel limit on a lathe so I didn’t do it right away. While playing around, I just assumed it would decelerate to a stop when nearing the switch. I assumed incorrectly.

That is incorrect.
If you have setup your machine correctly when you home the machine, It hits the home/limit switches and backs off of them, THEN sets machine zero. (press Alt-D) If all is setup properly, during normal operation, CNC12 will stop the axis AT machine zero and at the end of its travel(if software limits have been set correctly and yes, you need to setup soft limits in a lathe as well) before hitting the limit switch or hard stop.

What you are describing could be lost steps or misconfiguration. When that happens, the axis are no longer where CNC12 thinks they are. (Open loop system) lost steps can be caused by rapids that are too fast, acceleration to fast for the steppers/machine, taking too aggressive a cut and stalling the motor, binding in the drive system, not picking the correct stepper motors for the machine/control configuratoin, software misconfiguration, are a few examples.

Prove this to yourself, you did a video of your lathe homing to the switches. Once its homed, in slow mode, jog away from the switches a half inch or so and then deliberately come back to them. It should stop right where machine home position was set and not touch the switch.

Report back.
Marty

Here’s a video with no soft limits set. Maybe I don’t fully understand what’s going on but I’m confident I have no lost steps on Z. If I do a rapid jog, it will slam into the switch and damage it...that I’m sure of because I’ve done it. Once soft limits (or travel...whatever it’s called) ARE set, then it knows where the limit switch is and will decelerate in time to not crash and the Z DRO will show zero, not some positive value. Without soft limits set, it will stop once the limit switch OPENS, but on a fast move, it takes too long to stop. Not sure if this is a result of using steppers and not servos.
http://www.youtube.com/watch?v=MNRPkvwlCwE

[martyscncgarage]

Yes, a properly configured system including soft limits works.
Marty

[ScotY]

I’m not disagreeing with that. My point was you NEED to set soft limits even if it doesn’t seem to make sense, like for a lathe setup or Z on a mill. Otherwise, you CAN fast jog into the switch and crash.

[martyscncgarage]

I’m not disagreeing with that. My point was you NEED to set soft limits even if it doesn’t seem to make sense, like for a lathe setup or Z on a mill. Otherwise, you CAN fast jog into the switch and crash.

I'm sorry, yes that is correct. It's part of the setup process. Control needs to know the travels of the machine.

[frijoli]

I’m not disagreeing with that. My point was you NEED to set soft limits even if it doesn’t seem to make sense, like for a lathe setup or Z on a mill. Otherwise, you CAN fast jog into the switch and crash.

I think the confusion comes from the fact that people think of "home" as a maximum travel position. It isn't.

What it in fact is, is a reference point for the machine zero.

Clay