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General Metalworking - All aspects of working with metal.
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Posted by Jon Elson on September 10, 2008, 11:17 am
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Ivan Vegvary wrote:
> I think I diagnosed the problem. (Partially)
>
> The wires running through the flex conduit (3-#10's and one bare copper
> ground) are always hot. One of the three wires (white in my case) carries
> the higher voltage of the three phase. The lathe is well grounded through
> the bare copper wire. When I am welding (stupid thing I will never do
> again) I must be inducing a high current which returns through the bare
> ground wire. This bare wire heats up and melts the insulation on the
> adjacent high leg (white). The two melt together, and yes, I do blow the
> cartridge fuse on that leg only.
>
OK, this is exactly as I had thought. But, there has to be
something about your welder making that "ground" cable not be
ground. It doesn't make much sense, but if the ground cable is
truly grounded to the welding machine, and is in good condition,
then there should be only small leakage to other grounded stuff
such as the lathe. Maybe, however, even "small" leakage,
relative to the full welding current, is enough to really heat
up some #10 wire.
> This scenario happened identically both times (ground and hot leg melted
> together within the flex). The thing that I cannot figure out is why the
> current from the welding wire (MIG) would choose to go to ground (from part
> being welded, to chuck, to spindle bearings OUCH, to lathe frame, to
> electrical bare ground wire) instead of the welding clamp a mere 2 inches
> away. Only somebody familiar with MIG circuitry could explain that to me.
Well, only three possibilities. One, the "ground" terminal on
the welder is NOT connected to frame ground, but has some kind
of circuits between the cable and ground. Seems really odd, all
welders I've used really had the ground terminal grounded. For
safely reasons, it really needs to be so.
Two, the welder itself is wired improperly, and the welder frame
is not grounded. I'd think you (or your next of kin) would know
about this one by now. But, since this has come up, it really
seems like something that should be checked.
Three, the ground cable is shot, or maybe just loose. If
there's no other path, it works well enough to weld. If there
IS another path, the welding current divides.
Jon
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Posted by robert on September 10, 2008, 12:15 pm
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had wiring smoke on my 9x20 lathe a few years back....
motor smoked ...switch went....
$175 later for the parts/repair
i feel your pain
xman
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Posted by Martin H. Eastburn on September 10, 2008, 10:21 pm
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Current flows in the least resistive path. It might have been your belt buckle
to your sweaty body... caution!
The chuck had a hard grip on the metal...roller bearings have wide surface...
The clamp might not have the surface contact that you think. Perhaps only
points contacted and the chuck was lower than the points.
Your return on the MIG is likely not a number 10 or better. If so, perhaps
the wires in the clamp are broken or just points on the clamp.
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/
Ivan Vegvary wrote:
>> Still machining a part for my cement mixer. Needed to build up a 10" long
>> shaft back to 3/4 inch diameter. Thought I would put it in the lathe
>> (1947± LeBlond Regal 13"), run a few beads over the necked down area with
>> the MIG and then turn it down to size. I just need to build up about a
>> two inch length near each end. Anyway, did the above, turned on the lathe
>> and it doesn't work. I have real 3-phase running the lathe, and a
>> separate 240 volt circuit for the MIG.
>>
>> After a lot of sleuthing I found that one of the legs of the 3 phase had
>> shorted to ground. The short was in the 6 foot long flex between the
>> lathe and the 3-phase fused disconnect box. I figured that maybe I had
>> crammed too many wires (3-# 12's plus a bare ground) into the 1/2" flex
>> and things got too hot. It has served me for over 12 years. Replaced it
>> all with a 3/4" flex using #10 gauge (3 each plus ground). This time,
>> while using the MIG, I heard popping even before turning on the lathe.
>> The 3/4" flex was warm and the wires melted therein.
>>
>> Okay, I'm smart enough that I won't be using my lathe as a welding
>> fixture. BUT, what the hell is going on. Why would I create current in
>> the lathe feed wires. My ground clamp for the MIG was on the shaft within
>> 2" of the weld. BTW, both times it was the 'high' wire of the 3 phases
>> that melted. Two of the wires carry 120 volts to ground each, and the
>> third wire carries more.
>>
>> All explanations appreciated. Get to make up another feed for the old
>> machine.
>>
>> Ivan Vegvary
>
> I think I diagnosed the problem. (Partially)
>
> The wires running through the flex conduit (3-#10's and one bare copper
> ground) are always hot. One of the three wires (white in my case) carries
> the higher voltage of the three phase. The lathe is well grounded through
> the bare copper wire. When I am welding (stupid thing I will never do
> again) I must be inducing a high current which returns through the bare
> ground wire. This bare wire heats up and melts the insulation on the
> adjacent high leg (white). The two melt together, and yes, I do blow the
> cartridge fuse on that leg only.
>
> This scenario happened identically both times (ground and hot leg melted
> together within the flex). The thing that I cannot figure out is why the
> current from the welding wire (MIG) would choose to go to ground (from part
> being welded, to chuck, to spindle bearings OUCH, to lathe frame, to
> electrical bare ground wire) instead of the welding clamp a mere 2 inches
> away. Only somebody familiar with MIG circuitry could explain that to me.
>
> Thanks,
>
> Ivan Vegvary
>
>
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Posted by David Lesher on October 9, 2008, 1:37 pm
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A) How did you clamp the MIG ground to a rotating shaft?
B) CYA #1: Connect all the metal frames in your shop with a separate ground
strap to a known ground. If fuses blow, you just saved your life.
C) How can you have a white whire as a hot? That's evil, at least. [This is in
the US?]
D) CYA #2: Can you clamp the piece so it's insulated from the chuck? That will
solve the issue, but when the MIG won't work, you'll need to fix its ground
cable.
E) I too fear for your lathe's bearing...
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
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Posted by Mechanical Magic on September 10, 2008, 11:09 pm
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See my response, #3.
Dave J.
> I think I diagnosed the problem. =A0(Partially)
>
> The wires running through the flex conduit (3-#10's and one bare copper
> ground) are always hot. =A0One of the three wires (white in my case) carr=
ies
> the higher voltage of the three phase. =A0The lathe is well grounded thro=
ugh
> the bare copper wire. =A0When I am welding (stupid thing I will never do
> again) I must be inducing a high current which returns through the bare
> ground wire. =A0This bare wire heats up and melts the insulation on the
> adjacent high leg (white). =A0The two melt together, and yes, I do blow t=
he
> cartridge fuse on that leg only.
>
> This scenario happened identically both times (ground and hot leg melted
> together within the flex). =A0The thing that I cannot figure out is why t=
he
> current from the welding wire (MIG) would choose to go to ground (from pa=
rt
> being welded, to chuck, to spindle bearings OUCH, to lathe frame, to
> electrical bare ground wire) instead of the welding clamp a mere 2 inches
> away. =A0Only somebody familiar with MIG circuitry could explain that to =
me.
>
> Thanks,
>
> Ivan Vegvary
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>
> The wires running through the flex conduit (3-#10's and one bare copper
> ground) are always hot. One of the three wires (white in my case) carries
> the higher voltage of the three phase. The lathe is well grounded through
> the bare copper wire. When I am welding (stupid thing I will never do
> again) I must be inducing a high current which returns through the bare
> ground wire. This bare wire heats up and melts the insulation on the
> adjacent high leg (white). The two melt together, and yes, I do blow the
> cartridge fuse on that leg only.
>