Thread: How to ground to the rotating plate on a welding rotator?

I remember Dad and one of his welding engineer buddy's he did work for, make a rotating ground using Mercury! One of the best grounding devices I've ever seen. Didn't last long, a idiot worker turned in a complaint. They were forced to take it out of service!

Welding current through bearings can hurt them. I once had the yoke on an automobile throwout bearing welded and the welder just laid the bearing flat on his table and welded away, ruining the bearing. Of course, that was a ball bearing with very small contact points. That many rollers with a lot of weight keeping them in close contact can absorb a lot more current without damage, but it is a matter of capacity rather than an either-or situation.

The spring loaded grounding strap is a great idea, maximum contact area for minimum investment. I agree with Neilho that isolating the bearings would give a little more insurance.

Re conductivity, the scans are from Engineering Materials and Their Applications by Flinn & Trojan. Note that the chart is a logarithmic scale, so the common alloys in the middle are under 25% of copper's conductivity. Adding 5% zinc to copper to make yellow brass lowers the conductivity over 40%.

Bill

Bearing damage on a welding fixture will Happen..... So what... They are barely turning as opposed to say a car axle at 70 MPH. Check them every 500 years or so to see if they still turn. For that matter get a well used set of automotive wheel bearings as your starting set.

5¢

maybe i'm just a dumb ass but why would the current want to go through the bearings if your ground strap/brush is contacting only the rotating table? where exactly is it headed to?

The whole metallic assembly including fixtures and parts acts like a large array of parallel resistors. In other words Some current will flow thru each contact point. The ground Strap/Brush is merely an attempt to control where most current will flow

5¢

Originally Posted by Forrest Addy

Zagnut one thing you have to remember about RC stuff ratings: there's more outrageous ratings lies perpetrated on a faithful following of RC enthusiasts than political parties, televangelists, and penile enhancement hucksters combined. They probably make stuff from "billet" too.

100 Amps on battery RC stuff my a$$. You can't even draw 50 amps from the li-po batteries they use with a dead short. Apparently internal resistance just doesn't happen to RC batteries. RC batteries are capable of impressive current pulses but 100 Amps? Even for an instant? It's just an unprovable number to awe the gullible.

Anyway, one can overload carbon brushes. They just heat up a little or a lot depending.

i'm not talking about mass produced junk hyped up for the billet car kiddies but cutting edge competition stuff like composite airframes that would make even burt rutan cry. lately though the F5B competition has been neutered with all kinds of stringent limits on power and batteries to keep it from becoming an all out arms race between tuners like control line speed and tether cars which i'm sure you are familiar with. pretty sure they are limited to 1,750 watts now....or maybe it's a safety thing, what they used to do with nicads was just plain scary.

now, what if i told you that unpowered RC sailplanes are currently flying faster than 450MPH?

Originally Posted by WHHJR

For that matter get a well used set of automotive wheel bearings as your starting set.

The bearings, cassettes (the gold thingies holding the bearings) and shaft (40mm OD X 2.5mm wall) on my positioner are left over bits from my GoKart racing days. IMO, much cooler than some raggedy a$$ car wheel bearings.


Rex

As others have mentioned, insulating the bearings will protect them. This is done to larger electric motors as a matter of course, since the circulating currents that can get generated from unbalanced fields will otherwise destroy the bearings. Just make a bearing housing that can have a paper gasket between it and the frame and use insulating sleeves and washers on the bolts.

A steel trough of mercury with a steel paddle conductor is the ultimate, but people don't seem to be able to evaluate risks properly these days...

Rex,

Could you make photos of the whole rotating fixture of yours with some detailed views? A brief description wouldn't hurt either.

Nice grounding idea, by the way!

Thank you.

Mike

Originally Posted by ZAGNUT

now, what if i told you that unpowered RC sailplanes are currently flying faster than 450MPH?

Down!

"It's the only true direction"

;-)

Originally Posted by bjorn toulouse

Boy howdy, James, if my Nanosemantic Folicular Spliterizer (Pat.Pend.) wasn't down for annual maintenance you'd have an argument on your hands!


Rex

Sure, take the easy way out. You were not going to win the argument. I was not really trying to start one, it just surprises sometimes the amount of people that believe that statement, and I really did like your solution, good way to carry most of the current.
James

Originally Posted by CalG

Down!

"It's the only true direction"

;-)

i believe they are actually clocked during climb

here's a big one you can actually see in the vid:
The incredible ThunderMaster goes 425mph!! - YouTube