Proper and complete grounding

[letterman7]

Hi all,
Not much on the forums for posting.. mostly perusing existing problem solving :-) An interesting phenomena happens from time to time on my Bot - an ancient PRT, running from an updated control box. My machine sits on a concrete floor (well, the leg posts) and I have a 12 gauge copper wire running from one corner bolt of the rail out through the wall and onto a metal stake driven into the ground as my "ground". 99% of the time the machine runs flawlessly.. until that 1% that happened today. Much of my machine work is with Duna or Signfoam HDU board which can build up some static, but not as much as pvc. I do not use a dust collection system - I'm still working on a system that I like and I prefer to see the cutting bit while it's working. Anyway, many items I do involved cutting .stl files, which are the 2.5D dimensional images which can take hours to carve. Today, I was finishing an 18 hour job (cut 12 - hit pause, let the spindle cool down and restart next morning) which involved two passes of the cutting bit. I was there when it hit the 50% mark which is when the spindle etc would normally go back to the starting mark on the job and do the second part of the carve (depth) when the machine paused at 50%, started to make it's move back to the zero mark and stopped dead in a odd buzzing sound. No errors on the computer screen showed. But the machine started the second part of the carve where it came to a halt - obviously not in the right spot. Since I was there I was able to E-stop it and keep it from destroying a very expensive piece of material.
So, my though is that it is not nearly grounded enough, especially in times of high humidity like we've been seeing for weeks here. I've read on here that at least one member has ground straps from the spindle to carriage; Z carriage to Y carriage; Y gantry to X rails and each leg individually grounded to the table/rails. And then all that tied to a common ground plate somewhere. Seems excessive, but I get it. Does anyone have even a sketch on proper grounding - where everything should be grounded, if there is such a thing? I know metal to metal is paramount; I just don't quite know what would be considered the best way to get everything to earth.
Thanks!
Rick

[dlcw]

You need to run a ground wire from every part of the machine that does not have a DIRECT metal to metal connection. For example, a ground wire from bare metal on the spindle to bare metal on the Z car. Then a ground wire from bare metal on the Z car to bare metal on the gantry. then a ground wire from bare metal on the gantry to the rails. All the legs that don't have metal to metal contact should have a grounding wire tying them to each other. Then a ground wire to a common ground plate that your computer and table or connected to. Then a good ground wire to an outside ground rod. Also, a BARE ground wire from bare metal on the dust collector, thru the inside of the dust collector hose to your common grounding plate. This will shunt static.

The goal is to have each piece of the machine that is not already metal to metal connected, connected by a good grounding wire. I use 12 gauge green for my grounding wire.

[jTr]

2 points:
1> I had recent problems similar to yours. SB support advised full remove/reinstall of SB3, then, if still experiencing issues, based on age, my control computer internal hardware was failing (at 9yrs old)
Turns out, it was the latter. I paid $600 for a Shopbot prepared laptop, which they will do upon request now. A month later, I am cutting with confidence again - machine really smoothed out too.

2> To more directly answer your question, based on above issues, I too sought proper grounding and found this awesome, thorough write-up that I wish I'd known about years ago:

https://www.shopbottools.com/ShopBotDocs/files/Grounding%20your%20tool%202012%2008%2007.pdf

It is precisely what you're looking for, and I don't doubt that it contributed to better performance for my 2011 PRS Alpha.

Good luck!

Jeff

[coryatjohn]

High humidity means low static. It's the dry air that is more problematic for static. I suggest it's not a grounding problem.

[letterman7]

2 points:
1> I had recent problems similar to yours. SB support advised full remove/reinstall of SB3, then, if still experiencing issues, based on age, my control computer internal hardware was failing (at 9yrs old)
Turns out, it was the latter. I paid $600 for a Shopbot prepared laptop, which they will do upon request now. A month later, I am cutting with confidence again - machine really smoothed out too.

2> To more directly answer your question, based on above issues, I too sought proper grounding and found this awesome, thorough write-up that I wish I'd known about years ago:

https://www.shopbottools.com/ShopBotDocs/files/Grounding%20your%20tool%202012%2008%2007.pdf

It is precisely what you're looking for, and I don't doubt that it contributed to better performance for my 2011 PRS Alpha.

Good luck!

Jeff


Interesting. My upgraded control box is only a year old or so. But, my installation of SB3 is older than that. I'll look into a complete re-install just because. And thanks for the link/.pdf!

[letterman7]

High humidity means low static. It's the dry air that is more problematic for static. I suggest it's not a grounding problem.


:-) Have you ever cut HDU? Believe me, it generates it's own electrical charge. The machine is covered...

[RobbyFirstBuild]

I believe he was referring to the fact that dry air is more static friendly versus humid air.
You are correct though, some plastics generate lots of static electricity.
I have considered trying some anti-static spray such as Cling to see if that helps, but haven't tried that.

[letterman7]

Yes, I understand humid vs dry air. It could be pouring outside and I'd still have stuff flying up and sticking to the metal :-) And I've done the Cling/Static-guard thing.. only helps for a few minutes. Interestingly, I was talking with a supplier today who runs 2 large frame MultiCam machines, both sitting on a concrete floor. He has vacuum hold-downs and uses MDF for a spoilboard. We were talking about static issues and he said that he's never ever had a static problem, no matter what he was cutting.

[fredtoo]

This may not apply to this thread but my understanding of grounding, particularly when digital communications is involved, is that ALL devices (Shopbot, computer, dust collector, etc) must be grounded to the same common ground. If a common ground is not used then a 'ground loop' can occur causing all kinds of comm issues. See Wikipedia: https://en.wikipedia.org/wiki/Ground_loop_%28electricity%29

[letterman7]

This may not apply to this thread but my understanding of grounding, particularly when digital communications is involved, is that ALL devices (Shopbot, computer, dust collector, etc) must be grounded to the same common ground. If a common ground is not used then a 'ground loop' can occur causing all kinds of comm issues. See Wikipedia: https://en.wikipedia.org/wiki/Ground_loop_%28electricity%29


Absolutely applies to this thread! In fact, it's been discussed in another thread not far below. And that never occurred to me.. I thought ground was ground, so yesterday I took the minor step of taking my "ground" wire that was buried in soil, snipping it short to be close to the machine and attaching it to a modded three wire extension cord (primary prongs were cut off so all that was left was the ground prong) and plugged it into the circuit with the other equipment. We'll see. I still am going to take the extra step of using flexible copper ground cable on everything else to tie everything on the machine together, I just have to order everything.

[dlcw]

Ground loops are a big problem when grounding. When it's done properly, you will eliminate ground loops. The idea is to make sure that you are not relying on a connection between two parts, that are painted, to be grounded. They are NOT. Only bare metal to bare metal will provide the necessary grounding that prevents those loops.

We had instances aboard Coast Guard ships where there was constant rattling sounds coming across HF receivers. We traced it down to places on the ship where there was an opening in the ships railing that were closed using chains. These chains rattled as the ship rolled and pitched causing the noise over the radios. We ran a ground wire from one stanchion to the next basically providing a ground that eliminated the rattle chains. Another area was where metal ladders connected to the decks. Again, rattling of the ladders caused noise in the HF radios. We put a ground wire between the ladder and the deck, bypassing the rattling pin and eliminated the noise. In my amateur radio setups, I put in grounding systems that were fairly complex. As grounds are part of an antenna system, my antennas performed much better because of proper grounding.

Since applying the grounding methods I learned from 23 years in military electronics and another 11 years as an amateur radio operator, my ShopBot has run pretty well. Still get occasional brain farts from the ShopBot. That just stems from archaic connection technology between PC and controller.