Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

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ScotY
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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by ScotY » Sat Dec 02, 2017 11:02 pm

It’s only the Y axis that I’m having problems with, because I have the switch on the “wrong” side.

cnckeith
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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by cnckeith » Sat Dec 02, 2017 11:08 pm

Scoty i think you are confusing Part Zero location with Machine Home Zero location. these are two different zero points!
Machine Home by definition is machine ZERO. But that is NOT the same as Part (WCS Work Coordinate System) Zero.
When the machine is done homing the DRO (Digital Read Out) is displaying the distance the tool is from PART ZERO (WCS). (You can set the part zero location anywhere you want on the machine using the part setup menus F1 setup, F1 Part etc..)

Once the machine is homed out, pressing Alt D will show you that the machine coordinate system is at X0Y0Z0 when the machine is at the home position.
Jogging to the other end of the axis travel and stopping just before the axis hits a hard stop will produce the number on the DRO you need to enter into the software travel limit values in the wizard.

CNC programmers do NOT use the machine coordinate system to program parts. you use the Work Coordinate System to make parts.
so press Alt D again to switch out of machine coordinates back to the WCS and set your part zero position where every you need to on the machine to make parts!

oh.. and there is no such thing as having the home switch on the wrong side:-) you can put it on either end of the axis. no problem.

here in this old video when i had hair.. i talk about homing and part zeros..

https://youtu.be/mA41pUyONJM?t=6m23s

ScotY
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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by ScotY » Sat Dec 02, 2017 11:26 pm

Okay, I think I finally get it re. part zero being the important thing for running a program...all the movement is based on part zero.

So, when I home the machine, it’s okay for the machine to be at a physical X0 Y5 Z0 and yet the DROs will show X0 Y0 Z0 for machine coordinates? The table won’t be in the “normal” location, far right and all the way back but, rather, far right and all the way forward. I can then set part zero to wherever it needs to be and all will be good?

Is my thinking fixed now? :lol:

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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by ScotY » Sat Dec 02, 2017 11:33 pm

Ah, I get it now! All movements, such as MDI commands are based on WCS. Thanks for setting me straight! :)

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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by martyscncgarage » Sat Dec 02, 2017 11:34 pm

Boy, if it was me, I would mount a switch on the front of the saddle and put a tripper in the slot on the front of the table like my big mill for the -X switch....but that's just me.... ;)
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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by cnckeith » Sat Dec 02, 2017 11:38 pm

yep.. you got it.

what's most important is tool position relative to part zero (wcs) and that is what the dro displays.

when done homing the DRO is showing you the distance the tool is currently at from the last part (wcs) zero position that YOU set. If the DRO is not reading what you want.. then go set the part zero where ever you need it to be!;-)

the machine coordinate system runs in the background, the DRO displays position of tool relative to part zero not machine zero.
(knowing the position of each WCS relative to machine home is a useful thing but i'll save that for another discussion.)

please watch the training video links i posted above that show setting part zeros, tool offsets and part programming..they are old videos but the concepts still apply.

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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by cnckeith » Sat Dec 02, 2017 11:46 pm

these pages from Fusion 360 Fundamentals of CNC machining might help with understanding Machine vs Work coordinates.. see attached.
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Pages from Fundamentals-of-cns-machining autodrsk fusion 360.pdf
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ScotY
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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by ScotY » Sun Dec 03, 2017 12:17 am

Thanks, guys...appreciate the help! I’ll watch the video and read the attachment.

Marty,
I’m working on the Y limit switch. The pic you show would work well for X, but would it apply to a Y switch? If so, I’m quite now sure how you’d do it like that. The pic I posted is not the actual orientation the Y switch will be mounted. It took me a while to decide, but I’m very lazy and try to figure out the easiest way that still makes sense. :lol: And that’s just the general location of where I want to put it.

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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by martyscncgarage » Sun Dec 03, 2017 12:24 am

ScotY wrote:
Sun Dec 03, 2017 12:17 am
Thanks, guys...appreciate the help! I’ll watch the video and read the attachment.

Marty,
I’m working on the Y limit switch. The pic you show would work well for X, but would it apply to a Y switch? If so, I’m quite now sure how you’d do it like that. The pic I posted is not the actual orientation the Y switch will be mounted. It took me a while to decide, but I’m very lazy and try to figure out the easiest way that still makes sense. :lol: And that’s just the general location of where I want to put it.
X when it comes to a CNC machine, take the time to do it right and use good parts. Will save you frustration in the long run.
That was my X axis by the way. Might have worked well on your machine and not taken all that long to install.
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ScotY
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Re: Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

Post by ScotY » Sun Dec 03, 2017 1:45 am

Yes, I’ve seen that type of switch setup done before and I was actually going to do the same but found an easier way that works for me. I’m not using fancy limit switches but I think they’re good enough for my toy machine. Now that I finally understand, the Y switch will be equally easy to install and then I will be all that closer to being done!

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