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Z axis question.

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15 Mar 2021 15:29 #202359 by tommylight
Replied by tommylight on topic Z axis question.

Great I’m getting more understanding. So now my last question do you recommend using the same pin for upper and lower limits + homing Are there any disadvantages to this setup?


I'd have to look at my setup, but I'm pretty sure I have my sensor set up as a home + limit switch. First it's a home switch, and after it's homed it becomes a limit switch in LinuxCNC.

As I mentioned, I have no sensor on the lower limit. I rely on LinuxCNC's Soft Limits to take care of that for me. Works great.

Same here on several machines, one sensor is max limit and home, no min limit switch on Z.
Do not worry about bottoming out, you will hear it ! :)
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15 Mar 2021 15:36 #202361 by Creative25
Replied by Creative25 on topic Z axis question.
How much the chance of damaging the machine when running into a hard stop.

Tearing can belts I use get a 4:1 reduction?

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15 Mar 2021 16:47 - 15 Mar 2021 16:48 #202372 by snowgoer540
Replied by snowgoer540 on topic Z axis question.

How much the chance of damaging the machine when running into a hard stop.

Tearing can belts I use get a 4:1 reduction?


If you use a home + limit switch, and properly set your minimum limit, you wont hit a hard stop. Unless you lose steps for some reason, which if you have things set up correctly isnt likely. Also, if you dont work right at the end of travel and work in the middle somewhere), then the float switch will also stop unexpected motion. Further, if you equip Z with a breakaway switch, you'll be even further protected.
Last edit: 15 Mar 2021 16:48 by snowgoer540.
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20 Mar 2021 20:18 #203028 by rodw
Replied by rodw on topic Z axis question.

What I actually wanted to know is one pin is ok or if it is preferable to have separate switches for homing and limit. Say in case the homing switch fails. Just wonder how common is it that a normally closed switch fails.


I have preferred seperate home and limits on all axes but run a shared home/limit on the Z axis becasue there is not enough room to run two sensors. It works fine, You do loose a bit of travel is the only negative. Be sure to move the axis away from the home switch with a home_offset otherwise the limit switch will trigger the moment you complete homing.

I did add a lower limit switch but once some material is placed on the table, it can never be triggered so would not bother again..
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21 Mar 2021 00:27 #203069 by phillc54
Replied by phillc54 on topic Z axis question.
FWIW I have never used physical limit switches with LinuxCNC, I rely on the soft limits only.

My plasma table is the first time I have used home switches, although with my little table it would be quicker to do manual homing without switches.
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25 Mar 2021 12:40 #203613 by Creative25
Replied by Creative25 on topic Z axis question.
There is this Question on my mind. On a plasma table what do you use for lubricating the ball screw on the z axis?

My concern is about oil attracting dust.

Sliding oil or some dry lube, like chain lube?

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