Homing & Limit Switch UNSOLVED MYSTERY! <solved>

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RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

I purchased a power drawbar kit. It came with a small relay. The directions suggest that when the drawbar is activated that the relay be used to break the E-stop circuit. I think they used the term "E-stop" with a different intention. Thinking back, I believe they were referring to the E-stop circuit on a manual mill that kills power to the spindle motor, not the E-stop on a CNC control circuit.

For what it is worth, about a year and a half ago, I started this cool hobby. I had never even touched a milling machine before. Since then I have learned a bunch of Fusion 360 Cad, some g-code and just finished converting this PM833TV to CNC. Now I am following the Titan Acadamy online building block series so I can learn how to CAM parts (https://academy.titansofcnc.com/categor ... ing-blocks). It's been a fun journey but as you can see, I have a lot to learn. I had no idea that the machine needs to be re-homed after the E-stop circuit has been broken.

Thanks so much for all your help. I am rewiring the mill as we speak.

All the best... Richard
tblough
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by tblough »

The Acorn is an open-loop system. As such. It does not receive feedback from the motors to know the actual machine position. It commands the motors to move to a certain amount and just expects them to do it. If it does not move the expected amount, or something external changes the machines position, the Acorn has no way of knowing.

Some motor drivers have the ability to send Acorn an error signal if they fail to reach the commanded position, but they still cannot tell acorn by how much they failed.

If you remove power to an axis, it can no longer hold position, nor can it signal Acorn there is a problem. My guess is your Z axis is slipping down when power is removed, and Acorn has no clue about this.
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

Thanks Tom. I appreciate the info.
suntravel
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by suntravel »

tblough wrote: Sun Nov 27, 2022 11:14 pm ...... My guess is your Z axis is slipping down when power is removed, and Acorn has no clue about this.
My guess is hard stop of Z is 0.375" above the home sensor and after e-stop the gas struts are pushing to the hard stop.

After releasing e-stop Acorn gets this new Z 0 position.

If the sensor would be wired as HomeLimitZ to a single input you would get an error Z Limit tripped.

If you want to use the safety feature of the draw bar, cut the power line to the spindle motor (not to the VFD) or cut the lines form the spindle start output.

Uwe
Gary Campbell
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by Gary Campbell »

As an alternative you could run the digital common (DCM) thru the relay between the VFD and the FWD and REV relays. This would cut off either signal to start the spindle.
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RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

Hello Gary,
I like your alternative to breaking the spindle power. I actually wired it this way last night but didn't love the idea for a number of reasons.

Just to be sure I understand you correctly, are you saying that if I break the VFD COM connection it will disable the spindle? Please see my attached VFD drawing. I put a red arrow where I think you are suggesting breaking the circuit.

Thanks... Richard
Attachments
9 - Pin DB9 Connector - VFD - Pinout Spindle Stop.jpg
tblough
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by tblough »

It doesn't "disable" the spindle, only prevents it from being turned on in forward or reverse.
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
RJS100
Posts: 380
Joined: Tue Oct 20, 2020 8:41 pm
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CNC Control System Serial Number: none
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Location: Arizona

Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

That works for me. Thanks.
tblough
Posts: 3072
Joined: Tue Mar 22, 2016 10:03 am
Acorn CNC Controller: Yes
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CNC Control System Serial Number: 100505
100327
102696
103432
7804732B977B-0624192192
DC3IOB: No
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Location: Boston, MA
Contact:

Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by tblough »

Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
RJS100
Posts: 380
Joined: Tue Oct 20, 2020 8:41 pm
Acorn CNC Controller: Yes
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: Arizona

Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

All set! I wired the power drawbar as suggested by Gary to break the DCM connection and all is working great. Thanks again for all your help. Now you got me thinking about limit switches. I will post this topic separately.

Thanks... Richard
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