Purchased the Probe from Openbuilds and am using on an Anolex 3020 with their 1.5kw VFD. I’ve read the threads on bad wiring and $6 options… Here’s what I’ve narrowed it down to: I check voltage on the probe terminals on the PCB and get -5v. Placing the magnet on the spindle lead gives me, of course, -5. Testing all around the chassis gives me -5, including the bed and the Al stock that’s clamped to it. I’m pretty new to this and I have no idea if that’s how it’s supposed to be. The hack to get it going has been to line the bottom faces of the probe with some blue painter’s tape. That keeps it from shorting and allows the code to run its cycle. But it’s not ideal. Any thoughts?
XYZ Probe Plus with VFDs and other ground-loop inducing components Finding and eliminating the bad wiring is key. How are you measuring? No negative voltages uses, perhaps just have probes wrong way round. 5V pull up is normal. Measure continuity not voltage. DC GND should not be connected to AC EARTH
Yes, I hear you. I suppose let’s start with the basics. If I attach the 5v lead to the end mill, is it expected that the entire machine becomes energized? I’ve sent a message to Anolex for their input. FWIW, red/black leads from the JST connector on the PCB, connected to appropriate meter probes respectively, read negative voltage. I can reverse easily enough. Ty.
Can't directly comment on a 3rd party controller. But in our BlackBox you'd have the plate as GND, the Magnet as SIG (With a 5v pullup) When magnet touches plate (via collet/endmill) it closes SIG to GND
I guess the problem is that the magnet energizes the entire machine and b/c the workpiece is aluminum, the plate closes the circuit as soon as I put it on the workpiece. For a piece of wood, it would be fine. And when I line the plate with masking tape, obviously that insulates it. But it’s still extremely frustrating.
which is why I use an optical sensor.... Optoisolated Z probe and I also think that the XYZ probe plate should have an optoisolator and battery in it so it is completely isolated from any and all machine grounds etc. I am hoping to prototype this in the next 6 months.
The answer is to use ultra thin shipping tape and give one wrap around the spindle. Then insert back into the spindle holder. That will isolate the spindle and keep the 5v from making its way to the plate prematurely. I’m trying to think of any desktop cnc (primary market for these devices) that has its spindle isolated from the rest of the machine and can’t think of one. Ergo, the plate is really only useful for getting work origin when on non-conductive materials. I feel like that should be highlighted, bold and underlined on the store page.
AC EARTH and DC GND should be seperate domains The probe runs on the DC domain. If you have EARTH shorted to DC GND its a safety issue firstly, and a nuisance secondly. Sort that out please, skip the workarounds and fix the root problem. The spindle should be EARTHED. Plate is DC GND. In a correctly wired setup it would be isolated and no way to complete the circuit by accident just by placing SIG on the collet.
Peter, I have taken apart my VFD enclosure to inspect the wiring. Everything is apparently where it should be. I have traced with, per your instructions, continuity from spindle EARTH all the way through to IEC cable EARTH. I assume that the chassis of the mill is DC GND. Most areas of the mill are electrically continuous, including PCB standoffs, bolts, fixtures, etc. Before the tape ‘workaround’, this also included the spindle. In other words, I believe that EARTH and DC GND were connected (and I don’t see how that could be otherwise, in the case of all of these desktop machines, unless they usually include an insulator sleeve around the spindle). So I believe that the ‘workaround’ was the fix. Please tell me if I’m wrong. Back to the issue at hand; as far as I can tell, the software trigger is voltage drop below a threshold. With EARTH and DC GRD isolated by the tape insulator, clipping the 5v SIG to the spindle measures 0.5v back to DC GND. Indeed, from IEC cable EARTH, I measure 5v (unplugged from the wall)! If I start the probing routine, of course, it fails immediately (0.5v clearly below the threshold). However, I f I reverse the wiring and send the 5v SIG to the plate and use the magnet as DC GND, the probing routine completes perfectly. Yes, this temporarily connects EARTH with DC GND. But I f I can’t probe from the tip of the end mill, what would be the point of any of this? Sorry. I’m new to this. Regards, Michael PS If you suspected the same thing that I did, you’d be right. Disconnecting the IEC cable from the wall precluded the 5v from draining into EARTH and I was able to measure the full 5v back to DC GND (and not the 0.5v when the cable was in the wall). The probing routine completes. That said, if the insulator wasn’t between the spindle and the spindle holder, touching the XYZ plate to anywhere on the chassis would prematurely end the routine… As far as I can tell, this all comes down to a piece of tape.
Multimeter for continuity between AC EARTH and DC GND. Should show open circuit. If not, something is shorting DC GND to AC Earth somewhere Tape as a solution? With the whole machine connected to DC GND, a thin piece of tape is what you bet your electronics, and possibly your life on - someday when a RCD in your house malfunctions on the same day the dryer element develops a ground fault. Do you trust your "thin tape" has the correctly rated insulation values to keep it all safe? Do you trust your electrical install enough? Further, should wonder - why if there Shouldn't be a path between DC GND and AC Earth, is there one? Is it a failing PSU about to leak mains into the DC side? Bad Wiring? Chaffed through cable touching metal frame? If what should not be, is, it should not be. https://control.com/technical-articles/negative-effects-of-grounding-earthing-a-dc-power-supply/ Spindle should be EARTHED. Machine frame can/should be EARTHED too. But neither should be connected to DC GND (GND and EARTH = seperate)
I think I’m understanding. Then yes, DC GND is not connected to the machine. There is NO continuity between the machine and GND on the controller power supply lead. I pulled it out slightly from the controller and tested for continuity… At this point, the machine is neither EARTHED nor Grounded. If I remove the tape and allow the machine to EARTH, the +5v from the magnet instantly drops to 0.5v and the probing routine instantly fails. ===Do you agree that sending +5v directly to EARTH would cause a voltage drop?=== If I reverse the wiring (again with the tape insulator removed) and use the magnet as DC GND: A: that connects it to EARTH which you say I shouldn’t do but B: it allows me to use the plate as SIG and to run the routine successfully (with exception —>). Again, if the plate is trying to find zero on something non-conductive, it works fine. If that something is metal, the plate earths, the voltage instantly drops and the probing routine fails. So I can either line the spindle or I can line the plate. I chose the spindle b/c I wanted to get the most accurate zero off of the plate. David, you seem to understand what I’m trying to convey. Am I way off-base here?
I understand that when you connect the magnet from the probe (which has 5v DC on it) to the spindle, the Blackbox then says 'probe connected' and you see a voltage drop. This means that the spindle is connected to DC ground. Peter is saying that it should not be connected to DC ground, and I agree. So, you need to figure out where there is a connection from spindle to DC ground and disconnect it.
Exactly. So on the OTHER end of the spindle body > earth wire in 3 phase cable > VFDs PE terminal > VFD mains input's Earth > House wiring > short of yet to be determined source > DC domain - current is flowing. There IS continuity between DC GND and AC earth, per your report. Current can't flow wirelessly. So look for the short. Take the tape off. Multimeter in continuity between DC GND on controller's Probe Input and the other probe on a known Earth (spindle body sans tape) It should show continuity. Now: process of elimination. Start unplugging less obvious stuff and see what breaks the short. Obvious stuff like disconnecting VFD earth, unplugging VFD etc will break the short. But thats valid paths, and Upstream of the ACTUAL short
Right. So I misspoke. I assumed that the machine was DC grounded. It is not. Please see my post from last night, prior to this one. There is no continuity, whatsoever, between the machine and DC ground. I did test for continuity between the XYZ plate and actual DC ground (slightly pulling out the DC power supply lead, from the control box and using the sleeve) which did test positive for continuity. So the plate is, in fact, going to DC GND. Presumably the NEMA motors are as well, limit switches, etc. I tested the exterior of the motors for continuity back to actual DC GND and it’s null. (Are they also insulated? I have no idea. Haven’t pulled one apart.) *I should define ‘machine’ as: the extruded aluminum, the bolts holding it all together, lead screws, linear ways, etc; the colloquial ‘machine’ as most people would think of it… The spindle, with ‘tape fix’, is electrically insulated from the ‘machine’. The controller is also electrically insulated from the ‘machine’. I took the cap off of the spindle and confirmed EARTH wire connected to a bolt (which is directly bolted into the spindle body). I traced that wire back to the VFD enclosure and opened it (pictured below, EARTH in purple perimeter). It is directly jumped off of IEC socket EARTH (the other jump going to the VFD itself; not in purple but visible). So as Peter stated, the spindle should be and is EARTHED. I have confirmed that by testing for continuity from the spindle body to the IEC cable EARTH prong (literally last end in chain before going into AC power strip which has ‘protected’ LED lit) What does ‘protected’ mean to TrippLite? I have no idea but assume that it means EARTHED…. If I removed the ‘tape fix’ insulator from the spindle > the ‘machine’, as Peter says “can/should be”, is EARTHED as well. Which brings me back to the question that I specifically highlighted: ===Do you agree that sending +5v DC directly to EARTH would cause a voltage drop?=== That is the crux of the matter, as far as I can tell. If the answer is YES, then putting +5v DC into the magnetic SIG and telling the controller to look for voltage drop would cause an instant fail. If we can all agree on that, then your original reply about your optoisolated probe and post Optoisolated Z probe makes perfect sense. I think Peter would make the distinction in your post that the spindle isn’t grounded but is rather EARTHED. But I think we’d be into semantics; you both mean the same thing. My background is in Hollywood post-production. Not electronics or electrical engineering. I’m doing my best to keep up. Thanks.
Sorry that was a typo: “If I remove the tape and allow the machine to EARTH, the +5v from the magnet instantly drops to 0.5v and the probing routine instantly fails” What I meant to say was regardless of whether or not the machine is EARTHED, attaching the +5v DC to the EARTHED spindle causes a voltage drop. Are you saying that that should not be happening? “Take the tape off.” Secondarily, I have checked everywhere around the EARTHED machine for continuity between EARTH and DC GND and have found nothing.
Then I don’t know what to say b/c if I run a lead directly from IEC cable EARTH (essentially house EARTH) to the +5v SIG, it immediately finishes the probing routine, z retracts, and the controller thinks it has found zero.
Normally no. So, again (last time for me, repeated it enough times now) that is a CLEAR indication that the spindle body is providing some path to DC GND. Which it NORMALLY should not. Of course spindle should earth. Earth runs everywhere. Connects to other stuff like PC, or controller PSU, etc etc. The Spindle isn't the problem - its where-ever else DC GND is touching an AC EARTH. Above has specific tests, multimeter in continuity + selective unplugging. Just a matter of doing that
Right. Well, again, I’ve eliminated ALL of that and have gone directly from house EARTH to +5v SIG and it’s quite reproducible. Happy to send a video, if you like. The only last thing I can think of is to come FULL CIRCLE and consider the possibility that the controller power supply is shorting DC GND to EARTH. I can order a nice Meanwell 24v supply and trust that they’ve done their job correctly. Otherwise, I’m with you and am done with it. I’ll just brute force it and hope that I can get the parts that I need, without testing the current gods, and then be done with it all. Thanks! Edit: Nvm. I just tested continuity on the controller power supply between DC GND on its output with its IEC cable EARTH and the result is null. So that theory is out the window. At least I don’t have to buy an expensive power supply to find that out lol
Sorry. Don’t know if you saw my update. I tested for continuity between DC GND on the controller’s power supply output and its IEC cable EARTH and there was nothing. Honestly, I’m a little surprised that you’d say that DC voltage wouldn’t drop when connecting to EARTH. To my ignorant mind, electrons would flow. Let me ask you a different question: I remove the tape insulator and the spindle plus machine are all now EARTHED. I put the DC grounded XYZ plate on my aluminum workpiece. Aren’t I then shorting DC GND with EARTH? And also, wouldn’t closing that circuit cause the probing routine to fail completely? That was the reason this post was even started. It’s funny b/c when I was probing around, after your email this morning, I attached the SIG to the spindle and started reading 5v from the meter to GND. Puzzled, I then remembered to plug the VFD back into the power strip thereby reintroducing EARTH. Then the meter read the typical voltage drop to 0.5v I do appreciate your time, Peter. Thank you. You too, David.
Took one last stab at the VFD, thinking there may be some short between DC GND branching off to EARTH. Probed the EARTH terminal against everything and came up with nada. Pretty neat, little enclosure though…
Are you using a laptop and is it plugged into the mains? Ground loops on laptops is a known thing. Try unplugging the laptop from the mains. Alex.
Exactly. It must flow .... BACK TO THE SOURCE. It can't just seep out into the nearest blackhole, for current to flow the circuit has to be complete. Earth must be connected back to controller DC somewhere. "connected" is a vague term here - might be a high resistance connection not a dead short, but its definitely happening. In a normal setup Earth and DC GND are ISOLATED and NO CURRENT CAN FLOW. Yet yours does. We've definitely made enough mention that the VFD itself is unlikely, so we are going to ignore VFD comments going forward in the hopes you stop prodding around it We can only repeat advice so many times... +5V Pullup off SIG > Spindle Body > Normal earth path as expected (Same as all VFD machines, hundreds in use with our probe) - stays at pull up voltage. Nothing happens until the bit touches the plate, closing the path to DC GND. (In normal setups that's how it works) The issue happens after that somewhere - the current finds a path from Earth, back to DC GND. It has to, to flow current. If no current flows it can't drop down the voltage. A 10k pullup at 5V means less than 5mA needs to flow, so pure continuity measurement not entirely accurate, but the symptoms tells the whole story. Electron's Flow in a circle, back to the source. It can't radiate out into thin air just because its touching an earth. ONLY if the Earth is tied to the (DC Side) of the source, can it "flow"... Which it should not be. It might be through a bad PSU, a PC, chaffed through cable, a limit switch mounted to the frame in a way that the DCGND pin touches the frame, or any one of a million other things - spending more time on the VFD is just a waste of everyones time.
So this man walked into an openbuilds thread and suggested that it might be the laptop feeding the controller… and it totally turned out to be the laptop feeding the controller. Presumably USB GND… Good on you, mate. Did not see that one coming. And thank you. Big thank you!
Yes sir. Alex won the prize. Was the laptop… On the other hand, I’ve learned a lot from you. I’m in your debt. LEDs light up green and the probe does what it should. The last remaining piece to this puzzle is the aluminum workpiece. 5v SIG (w/ laptop disconnected from mains) remains 5v back to GND (problem solved). Without tape between the spindle OR without tape lining the probe, simply touching the probe to the aluminum workpiece ends the probing routine with an error. Is there any way around this? Is openbuilds planning a nonconductive version of the probe?
Well, it's all a bit strange. I've used 2 or 3 different laptops over the years - all plugged in to the mains when in use, with no probe issues. Currently I use a small desktop PC dedicated to the CNC and obviously always powered by the mains supply and no probing problems.
Yes, it's a problem with some laptops usb connections - don't ask me for technical details, I don't know them No known issues with desktops by the way. Alex.
It’s a Dell workstation laptop. It would have to be in its power supply, no? The USB is DC grounded and it loops back to the controller. Wild. I’ve mentioned multiple times, in this thread, using the probe on metallic workpieces and having it prematurely end the probing routine. At this point, having the other issue sorted, I can only determine that everyone knows and that no one wants to talk about it.
