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General Metalworking - All aspects of working with metal.
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Posted by bq340 on September 9, 2008, 9:27 pm
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UNLESS, the
> drum switch is bad and not all three legs are being shut on and off.
>
> Ivan Vegvary
>
>
It is common here to only switch 2 of the 3 legs & leave one directly
connected.
MikeB
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Posted by Martin H. Eastburn on September 9, 2008, 10:17 pm
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I suspect the armor cable.
Since it is on the floor (very likely) and might have been mashed
a little - the internal wires might be conducting through the internal
sharp edges. It might not be all of the time, just when it is pushed
back to sweep or ...
I'd take the wires from the fuse box to the lathe out of the cover
and inspect for holes or melted copper.
If the wires are good (before pulling - attach a nylon string to pull back
replacements (good idea anyway) or the original. There might be pin holes
punched through the insulation because the inductance of the motor and back
e-m-f that exceeds the insulation. e.g. using 600v wire on a 480 system
with 2or 3x emf spiking.
You might still have a faulty switch - but I bet the wire in the metal cover.
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
>>
>
> Here is a clarification to some of you who have replied.
> My three phase goes from the main panel to a fused disconnect box. From the
> disconnect box it went via metal flex to the drum switch on the lathe. The
> drum switch has three terminals and functions as OFF, FORWARD and REVERSE.
> It feeds the old GE low hp (maybe 2-3 horses) motor. The motor in turn
> drives the spindle through matched belts.
>
> I too cannot understand how a lathe, turned off at the drum switch could fry
> the feed wire between the fused disconnect box and the motor. UNLESS, the
> drum switch is bad and not all three legs are being shut on and off.
>
> Ivan Vegvary
>
>
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Posted by Jon Elson on September 9, 2008, 10:48 pm
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Ivan Vegvary wrote:
> Here is a clarification to some of you who have replied.
> My three phase goes from the main panel to a fused disconnect box. From the
> disconnect box it went via metal flex to the drum switch on the lathe. The
> drum switch has three terminals and functions as OFF, FORWARD and REVERSE.
> It feeds the old GE low hp (maybe 2-3 horses) motor. The motor in turn
> drives the spindle through matched belts.
>
> I too cannot understand how a lathe, turned off at the drum switch could fry
> the feed wire between the fused disconnect box and the motor. UNLESS, the
> drum switch is bad and not all three legs are being shut on and off.
Your flex-conduit has a spiral metal sheath that acts as the
safety ground, or at least a back-up safety ground. If that is
your only safety ground, it probably is high resistance. Your
"hot" wires likely were not "in circuit", but the safety ground
is always connected. My guess is welding current ran through
the flex-conduit to the panel and back to the welder, something
that REALLY shouldn't happen! It sounds like the current ran
through your spindle bearings, too, which is really bad news.
I'd check the quality of the entire welder ground cable, it may
be worn out or loose anywhere from the ground clip to where it
attaches to the welder. I can't imagine any other way this
could have happened if the ground cable on the welder was OK.
Jon
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Posted by Bob AZ on September 10, 2008, 3:13 am
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> Okay, I'm smart enough that I won't be using my lathe as a welding fixtur=
e.
> BUT, what the =EF=BF=BDhell is going on. =EF=BF=BDWhy would I create curr=
ent in the lathe
> feed wires. =EF=BF=BDMy ground clamp for the MIG was on the shaft within =
2" of the
> weld. =EF=BF=BDBTW, both times it was the 'high' wire of the 3 phases tha=
t melted.
> Two of the wires carry 120 volts to ground each, and the third wire carri=
es
> more.
>
> All explanations appreciated. =EF=BF=BDGet to make up another feed for th=
e old
> machine.
>
> Ivan Vegvary
Ivan
I think you mentioned your problem in the part of your query about
"creating" a current in your lathe feed wires. Check your grounding
paths. Don't use or rely upon any ground circuits using any part of
the flex. Period. And from your explanation of your "220" you don't
have a conventional 3 phase source. What you have is sometimes called
a wild phase or wild ground. This is OK under some circumstances but
certainly not with mixed use as you have with a welder and a lathe.
GFI protection would be prudent here also.
A solution is to have your power company or source upgrade your 3
phase so that each leg is the same voltage from ground. A separate
ground from the transformer is also provided to the user that the is
used as a source or safety connection for the neutral and the ground
rod you have installed. As it is two of your legs are 110 from the
center tap of one of the windings in the transfromer. This used to be
done to provide both 110 and 220, single and 3 phase, to the customer,
you, to keep costs low. For both the consumer and power company. Now
days true 3 phase is provided and a transformer is used to provide 110
and 220 single phase from 2 phases of the transformer. There are also
several other schemes to do this.
Another important thing to do is to upgrade your wiring so there is no
chance of the wiring in the flex giving problems. Don't under any
circumstances allow any possibilty of the flex to be part of your
grounding. Use a fitting to isolate the flex from becoming a part of a
ground loop. Remember flex is a mechanical item used to isolate
vibration and provide some mechanical protection from among other
things foot traffic. There are non-metal flex conduits available for
many circumstances.
Hope I said all this correctly at the middle of the night.
Bob AZ
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Posted by Ivan Vegvary on September 10, 2008, 10:45 am
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> 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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>
> Ivan Vegvary
>
>