Test for Ground?

[nat_wheatley]

I should know this by now, but how do I test my machine to see that it's grounded? I believe that it is, but I'm getting a lot of intermittant 'skipping' that I would guess is static related...

Thanks

[dana_swift]

If you have a volt meter, measure the voltage between the chassis of the bot, and a ground rod near your circuit breaker panel.

The AC voltage should be less than 1 volt. The DC voltage measurement should be zero or very close to it. If either the AC or DC voltages are greater than one volt, something is wrong. Then measure the current in the ground with a clamp on ammeter. It should show zero. If it is non-zero that indicates a ground loop.

What is the % humidity in your shop? In the summer with high humidity static is not as likely a problem.

Any possibility you have a loose pinion gear?

D

[gerryv]

Dana,
Interesting. Does this mean running a temporary wire between the bot chassis and the ground rod or does it assume one is present there, or have I perhaps misunderstood?

[nat_wheatley]

Dana, thanks for the info on the grounding.

I hadn't considered a loose pinion, but would love for that to be the issue. It's been very humid here, and also the issue has also seemed to get progressively worse, both which would point away from static being the issue.

I'll watch the machine tomorrow and see if the problem is unique to movement along one axis, and if so, then check the pinions. If it turns out it's not that, I'll go back to chasing static...

Thanks again.

[dana_swift]

Gerald- if your machine is near the breaker box, just hold one lead on the bot chassis and one on the ground rod. If its further away, extend one of the leads with a wire.

Hope that cleared it up :)

D

[nat_wheatley]

Pinons are tight.

Just noticed that my vacuum motors (4) aren't grounded, should they be?

[dana_swift]

Addendum on VOM checking ground:

After checking the voltage AC and DC, then check ohms, it should be very close to zero. One ohm or less would be expected.

---

Nat- as to the vacuum motors, I would ground them. Do you ever run the bot without vacuum? Does it change the behavior?

If there is a ground problem, it would do well to check the ground between the gantry and the frame, and the Z car and the gantry. Those two are bigger suspects, especially after some dirt and rust builds up on the rails and v rollers. Do you have a ground wire between all your bot components?

You might try air cutting the same file (router/spindle, vacuum and D/C off), does it skip then? If so the problem is mechanical or in the toolpath.

One other check can you hold on to your dust collection lines (especially the hose sections) without getting a periodic zap? Its hard to miss.. often causing creative use of the language ;)

D

[nat_wheatley]

Hi,

Can't really go without dust collection for the cutting I'm doing (3/4" melamine).

Machine has ground wire between all components.

Dust collector has metal duct work in all sections but a 10' hose drop to the machine. Solid copper wire with the hose.

It's pouring rain and 65% humidity, and I'm still getting a lot of this skipping. I've always had it now and then, but I'm seeing it 3 and 4 times per sheet (of closet panels)

I like the idea of air cutting a sheet, and see if it's doing it then. Will try that next.

Thanks

[coryatjohn]

65% humidity = no static problems. You can guarantee that unless you have one of those Tesla coils hanging around your shop.

[nat_wheatley]

I'll air cut a file tommorrow to see what happens there, but what are the other possible causes of this?

[dlcw]

Nat,

If you have grounding wires from all points on your machine to a common ground point and that ground point wired to electrical ground you should be good.

I have individual ground wires from:

- spindle
- gantry
- Z-car
- both X rails
- each individual leg
- each vacuum motor
- inside vacuum PVC pipe (bleed off any static)
- Inside dust collection hose
- Dust collector

Anywhere there is paint at a ground point, I remove the paint and sand the bare metal so it is smooth and then connect the grounding wire. I use lugs soldered to the grounding wire to ensure a GOOD electrical connection. I use lock-tite on all screws/bolts to ensure they won't vibrate loose. Lock-tite does not impede a good electrical connection.

Also, where the leg assemblies are bolted together, there is paint separating them (bad electrical contact). Because of this, I also tie the different parts of each leg together with a short ground wire. This ensures there is nothing on the machine that is not grounded.

All of these collect to a common point and then get tied to electrical ground. Don't have problems. I measure 0 ohms and 0 volts AC or DC between any point on the machine and the common ground point. I have eliminated all possibilities of a floating ground anywhere on the machine.

Learned all about grounding when in the US Coast Guard in the electronics field especially HF radio communications. A chain rattling on a ship can cause havoc in RF communications.

[nat_wheatley]

Don,

Now that's thorough!

I do have most points on my machine grounded, but could no doubt add a few that you've listed.

80% humidity in here today and I'm still getting the random 'clunk'....

[bleeth]

Nat:

Check over the way your grounds are run. They must be linear, as in ensuring that you do not have any ground looping occurring.
Regarding your hose wire: Is this a separate wire inside the hose and then grounded to your steel ducting? Does the ducting end up isolated by a plastic or painted collector or gate valve on the other end? This would prevent grounding. Assuming you have wire nuts tying ground wires at your machine together, open them up and make sure you haven't got a break that you can't see.

[dlcw]

For my dust collector I have a continuous 14 gauge stranded (not solid) wire that is connected using a soldered on lug at the Shopbot Z car and the chassis of the DC (HF 2hp).

Check the hose wire regularly as chunks of wood sucked up by the DC could create breaks in the strands resulting in loosing electrical ground integrity.

The chassis of the DC is connected to the common ground point in the system. The ground wire in the DC motor power cord provides motor grounding.

[nat_wheatley]

Just ran my table surfacing routine with the spindle and dust collector off. Several serious 'clunks' in both the X and Y direction.

I would think we could rule out static. What else could be causing this?

[steve_g]

Nat...
What happens if you slow your cutting speeds down some?

SG

[nat_wheatley]

Trying it now at 1/2 speed (4ips) will post back in a little bit...

[coryatjohn]

This is a silly question...

Does your controlling computer have the screen saver active? Is it doing anything other than controlling your SB?

[nat_wheatley]

Issue has disappeared at 1/2 speed...

[steve_g]

I suspected that might be the case... now you just need to find out how fast you can cut without loosing steps!

SG

[jerry_stanek]

What software are you running 3.6.xx or 3.8.xx

[nat_wheatley]

3.6.44

I've been cutting at this speed for 5 years at this speed and putting up with issue. I don't really want to slow things down....

Anything else I can try and change?

[jerry_stanek]

Try the 3.8.6 software it has helped some with the lost coms and other problems.

[nat_wheatley]

Wireless network adapter seems to have been the culprit. I just ran my table surfacing routing with spindle and DC collector off, and it completed the routing w/o issue.

A sincere thank you to Frank at SB and everyone that posted here, for helping resolve this. This one's been bugging me for a while, and I haven't been able to take the time to address it. Machine now appears to be running very smoothly.

Thanks again.

[jerry_stanek]

you may still want to try the 3.8.6 software I have boosted my speed and cuts are smother.

[nat_wheatley]

Thanks, I may but will say I'm hesitant. I've only loosely followed some of threads where people have had problems with some of the versions of the software.

I always like to try and have the most recent versions of the software I use, this being the one exception for the reason I've listed. Is the consensus that 3.8.6 is fairly issue free?

[dlcw]

I just bid a job cutting 18,000 parts per quarter out of 780 sheets of 1/2" MDF. Current configuration of 3.6.44 without ATC probably won't be the ideal setup. I wonder if 3.8.6 is stable enough to tie me over until I can afford an ATC. Also, wonder if 3.8.6 is REALLY stable with ATC.