Lathe with stepper motors - limit switch crash

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ScotY
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Joined: Sat Sep 23, 2017 7:57 pm
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Re: Lathe with stepper motors - limit switch crash

Post by ScotY » Sun Dec 24, 2017 7:21 pm

I have lots of confusion! :lol: This is just a hobby for me and the mill and lathe are just my toys. While I want it all working properly at some point, it’s the journey there that’s more important (and enjoyable, even when frustrating) to me. Thankfully, I don’t have to make a living doing this or I’d be broke! :lol:

martyscncgarage
Posts: 946
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CNC11: Yes
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Location: Mesa, AZ

Re: Lathe with stepper motors - limit switch crash

Post by martyscncgarage » Sun Dec 24, 2017 7:41 pm

frijoli wrote:
Sun Dec 24, 2017 7:17 pm
ScotY wrote:
Sun Dec 24, 2017 6:57 pm
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

👍
"Jack of all trades, master of none!"
Mesa, AZ

Centroid_Tech
Posts: 156
Joined: Thu Mar 18, 2010 2:24 pm

Re: Lathe with stepper motors - limit switch crash

Post by Centroid_Tech » Fri Jan 05, 2018 11:38 am

Let me try to clear the confusion. If both of the software travel limits, positive and negative, are set to 0, that is telling the control that there is no software travel limit set for either direction on that axis. When you home a machine, you are NOT actually setting a software limit. You are providing a reference so that the control knows where it is at. Yes, you can use a limit switch to home an axis. That is the typical configuration but you can also have a home switch that is completely independent of the axis limit switch. If a limit switch is used to home an axis, then one of the software limits will be set to 0 while the other software limit will have either a positive or negative value depending on which direction you homed that axis. With the software travel limits set correctly, the control will not allow you to hit that limit either via a program or jogging. If it's in a program, you will see a Travel Limit Exceeded message before it gets to that section of the program because of Centroid's lookahead feature. If you graph the part before actually running it, you will see that message if at any point in the program, it will pass that location. That is why I always like to graph the program first before actually pressing Cycle Start to run the job. If you are jogging, you will see that Travel Limit Exceeded message the moment you attempt to jog past that software travel limit.

With all of that being said, if the software travel limits are both set to 0, the software is unaware of any limits so the software will only stop motion once it hits the limit switch. At that point depending on how fast the axis was moving, it will most likely coast past that limit switch.

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