Yes, continuity between U,V,W is normal (required in fact). It's useful to know if your spindle is wired internally as a WYE or a DELTA configuration. In either case, continuity between each of the three windings is expected. You should check the resistance of each winding (interpreting the results differs based on whether your spindle is a WYE or a DELTA). Here is a link to a 3-phase motor testing overview www.electricalengineeringtoolbox.com/2015/12/how-to-test-three-phase-ac-motors.html . I recommend disconnecting the cable between your VFD and spindle, and verifying those wires do NOT have continuity with each other (that is where my fault was).

The gantry is too heavy even for NEMA 34 size stepper motors. The gear reduction trades speed for power. In other words, it takes more revolutions of the stepper motor to move the gantry a given distance but it is able to move it.

@@buildbug3979 Thanks for your reply, actually I was asking if we can use reduction gear couple with their teeth touching directly instead of using belt.

Exactly! I have 10mm multiples-all missing.

Yeah, the original tune up plan was to just replace the plugs & wires (they were original, so 96k miles on them). Sadly the #4 wire had corroded itself into the coil and refused to come out. When I finally stopped asking and pulled the wire out, the metal plug of the wire broke off in the coil. I tried to clean up the coil socket but didn't like the result so I decided to replace it and ordered the NGK coil.

@@buildbug3979 And how many miles on the NGK coil before it started acting up?

@@Blair62 It was about 700 miles

@@buildbug3979 Where did you order the replacement NGK coil from? Amazon? Ebay? Those sites have become notorious for counterfeit auto parts, NGK and otherwise. If a deal looks too good to be true IT IS.

These days I use OpenAI (gpt4) to find my documentation and present it to me as a guide

The latching circuit provides the following 1) it ensures the integrity of wires going through each e-stop switch (arguably a simple switch would do the same thing). 2) it requires a human to actively re-enable the latch when a fault or e-stop is triggered. This second feature is more important than it appears. Lets say you use a simple switch and at some point you hit the e-stop button which breaks the circuit & shuts off power to the machine. Without a latching circuit, the power will be immediately restored the moment the e-stop switch is reset. Perhaps this is fine for you but perhaps not. In industry and industrial machines this is usually NOT desirable. Think of a conveyor belt in a large factory. There may be other things that need to be done to safely re-set a machine to operate. This is why latching circuits are usually preferred.

Another great question. My design does NOT utilize dynamic braking during e-stop. There's a useful standards document created by National Fire Prevention Association (NFPA) that relates to this topic. "NFPA 79 - Electrical Standard for Industrial Machinery" ----------------- NFPA 79: 2018 - Link to full text - safetycents.com/safety-standards/ 9.2.2 Category 0 is an uncontrolled stop by immediately removing power to the machine actuators. 9.2.2 Category 1 is a controlled stop with power to the machine actuators available to achieve the stop then remove power when the stop is achieved. 9.2.2 Category 2 is a controlled stop with power left available to the machine actuators. 9.2.5.4.1.3 The emergency stop shall function as either a Category 0 or a Category 1 stop (see 9.2.2). The choice of the category of the emergency stop shall be determined by the risk assessment of the machine. ----------------- My design is an example of Category 0 - Uncontrolled stop. You are describing a Category 1 type system. You would need to design a circuit to tell the VFD to stop and then once the spindle has stopped, trigger the contactor to open. I don't have any design advice for you on this. I'd have to think about it. There may be some off the shelf solutions for this as it seems like a pretty common issue for industry.

This is a good question. At it's core, where you put the contactor determines what you think an e-stop button should do and what kinds of problems you think it is intended to address. As a safety engineer, if I could have the contactor be the first thing in my control cabinet I would. This would mean that no matter what kind of fault occurs downstream, if someone presses the e-stop button, the situation will be made safe (i.e. ALL motion stops, ALL power is cut from this machine/controller). This is the purest meaning of e-stop. Sadly this is not possible because I need some power to run the e-stop latching circuit itself. At first glance it's easy to think that an e-stop button should just stop motion (after all isn't that where all the danger is coming from). But I believe the e-stop should serve a larger purpose and make the area as safe as possible when something happens that NO ONE expected. For example, what if there's a manufacturing defect within the circuit breaker itself causing the chassis of the machine to be energized (as well as fail to open the circuit). If the contactor is downstream it will do nothing to make this situation safer. In short, it's impossible to predict all the things that can/will go wrong with a CNC machine and it's controller, the role of the e-stop system is to make the situation as safe as possible both mechanically AND electrically. Ultimately the design philosophy of your e-stop system is for you to decide but I use the following scenario to help guide my thinking. If my mother walked into the shop and found me on the ground and the CNC machine was making some horrible noise what do I want to happen when she presses the e-stop button. Sorry if that's a bit graphic but this is what I think a e-stop should be. This is also why I added a separate 'soft e-stop' button to my system which is really for the machine operator for the every day 'oops I forgot to do something', please stop motion so I can fix it type scenario.