Attachments :

CNCLatheElectronics-13758.pdf

I am using KFlop/SnapAMP in a lathe I am building right now from an optical table. I have got it running and made a couple of parts for testing.

So now that stuff works I am building an enclosure for the electronics, make proper connectors for all the cabling etc.

I don't know how to do the grounding properly. The attached PDF shows the system the way it is connected right now. I have the following specific questions:

- The brushed motor with tachometer is connected via a cable that has shielding. The shielding is not connected right now. Where should the shield connect? The enclosure, the motor, the CNC frame, the KFLOP ground...?

- I am going to mount an encoder on the motor to facilitate threading. The encoder is a bare unit in a plastic case similar to the US Digital/HEDS. I am planning to connect a cable with shielding, but I have the same question as above...

- Finally, I am going to add two glass scale encoders to provide closed loop operation for the steppers. The cable is already attached to those. I measure high impedance between the GND conductor and the Shield. The shield is connected to the case of the linear scale.

I would appreciate some education.

Hi,

Grounding and shielding is very complex.  My thinking is that there are basically two types of devices.  Noisy devices like motors where the shields are intended to collect and reduce the radiation of noise.  And quiet devices like sensors and encoders where the shields are intended to protect signals from noise.  I usually connect noisy device shields to Earth Ground as an attempt to divert collected noise away from critical electronics.  I connect quiet device shields to KFLOP DC GND near KFLOP usually at that end only to avoid ground loops and the possibility of current flow through the shield.

HTH

Regards

TK

 

I am using KFlop/SnapAMP in a lathe I am building right now from an optical table. I have got it running and made a couple of parts for testing.

So now that stuff works I am building an enclosure for the electronics, make proper connectors for all the cabling etc.

I don't know how to do the grounding properly. The attached PDF shows the system the way it is connected right now. I have the following specific questions:

- The brushed motor with tachometer is connected via a cable that has shielding. The shielding is not connected right now. Where should the shield connect? The enclosure, the motor, the CNC frame, the KFLOP ground...?

- I am going to mount an encoder on the motor to facilitate threading. The encoder is a bare unit in a plastic case similar to the US Digital/HEDS. I am planning to connect a cable with shielding, but I have the same question as above...

- Finally, I am going to add two glass scale encoders to provide closed loop operation for the steppers. The cable is already attached to those. I measure high impedance between the GND conductor and the Shield. The shield is connected to the case of the linear scale.

I would appreciate some education.

Hello Tom,
I believe you sent this email to the wrong guy, but it is great information and I will use it as soon as I get my Kflop and Kanalog boards.

Larry Bastianon
Sent from my extra large Samsung tablet

That helps a lot, actually.

It seems that I should really pay attention to the cables inside of the enclosure as well then? Right now the wires going to the motor connector are just 60Hz residential power wire (no shielding). But since they route pretty close past the KFLOP, should I replace that with shielded wire (shielding going to case ground....)

How effective is the shielding? Can I route the cables carrying the encoder signals in the same bundle as ones to the motors? Or is that bad practice?

Finally, a more general question. I have some wire here that has two shields. Inner conductors, then shield, then more conductors, then another shield. Right now, the inner wires are used for the DC motor on the spindle and its tachometer. If I don't use the outer conductors, are two shields better than one, or is the outer pointless? When I put the encoder on, can I use the outer conductors for it (then connecting the inner shield to case ground and the outer shield to KFLOP gnd?

Yes you should shield as much as the cable length as possible.

Shielding is very effective.  But you should always try to keep motor cables away from signal cables where possible.

I think you should avoid putting motor wires and encoder signals in the same cable.

Regards

TK

 

That helps a lot, actually.

It seems that I should really pay attention to the cables inside of the enclosure as well then? Right now the wires going to the motor connector are just 60Hz residential power wire (no shielding). But since they route pretty close past the KFLOP, should I replace that with shielded wire (shielding going to case ground....)

How effective is the shielding? Can I route the cables carrying the encoder signals in the same bundle as ones to the motors? Or is that bad practice?

Finally, a more general question. I have some wire here that has two shields. Inner conductors, then shield, then more conductors, then another shield. Right now, the inner wires are used for the DC motor on the spindle and its tachometer. If I don't use the outer conductors, are two shields better than one, or is the outer pointless? When I put the encoder on, can I use the outer conductors for it (then connecting the inner shield to case ground and the outer shield to KFLOP gnd?

Awesome. That lets me have a plan.

Thanks!