New member, new Journeyman (drag chains, dust collection, spindle grounding, ...)

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Hey Tom,

@TMToronto

From the reading I had done earlier I found that the shielding requirements for spindle/VFD are different. However, misinformation is plentiful as this thread highlights:

https://www.cnczone.com/forums/spindles-vfd/354362-still-bit-unclear-proper-spindle-grounding.html

@TMToronto

It doesn’t help that the Internet is full of seemingly valid information that regularly contradicts itself on all of these topics.

Yes, usually it’s a disease, that’s why I rarely approach things this way. Usually I buy literature used for engineering studies. My approach (in every matter) is to understand things. I achieve this mainly by rtfm rather than by visiting web fora. But web fora are nice if you meet someone that is exploring the same thing at the same time!

@TMToronto

Grounding is one of the most written about and misunderstood topics I have come across in my reading. Sometimes the different answers come down to ‘best practice’ vs ‘good enough’, as well as ‘industry’ vs ‘residential’ electrical codes, and so on…

That is a common phenomenon with a lot of topics: Everyone says something about it, regardless of whether he or she has studied it or just heard something about it.

I’ve been dealing with grounding for a long time and I would say, it is not rocket science.

When I said above that it could introduce a ground loop, I am aware that it may not always be relevant. A relevant ground loop is if your cable TV provider grounds its cable in his distributor board out there a few miles down the road and then you ground it again at your cable TV wall outlet. It can produce a lot of hum that deteriorates the signal.

Even if the housing of the spindle may be grounded via the bearings on the rails of the CNC, I would not consider this as to be the reliable way of grounding it. I would think that there must be an intentional electrical connection of correct dimension. Protective Earth (PE) has to carry any current that can appear erratically at any point on the machine.

Also there is a difference between circuit grounding, shielding and protective earth. Usually shielding and protective earth do not participate in the operational current flow. There may be assymmetrical signal or power cabling where shielding is at same time functional grounding, but to avoid ground loops, usually digital and analog signals use symmetrical (balanced) connections with separate shielding (or twisted pair if one wants to avoid shielding).

A 3-phase spindle is operated with three wires using a delta circuit, there is no Neutral conductor that has to be connected to ground. The fourth connector on the spindle, to which the spindle housing and the cable shielding are connected, is protective earthing.

@TMToronto

As an aside, which Mechatron spindle did you end up purchasing? I have not decided on a manufacturer yet - still need time to save some money.

I bought this one: HFS-8022-24-ER20 (Datasheet) (with Cooling Station)