Centroid Community CNC Support Forum

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

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.

Thanks Tom. I appreciate the info.

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

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.

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

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

That works for me. Thanks.

Just like in this schematic - https://www.centroidcnc.com/dealersuppo ... 158.r3.pdf

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