|
General Metalworking - All aspects of working with metal.
|
|
|
|
|
Posted by Ivan Vegvary on September 9, 2008, 7:04 pm
Please log in for more thread options
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
|
|
Posted by Wes on September 9, 2008, 7:45 pm
Please log in for more thread options
>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.
If there was a path that got into your lathes power wiring, I would be very
concerned
about the head stock bearings.
I'm not up to noodling out what may have happened at this time of night.
Wes
|
|
Posted by Mechanical Magic on September 9, 2008, 8:46 pm
Please log in for more thread options
The "ground" on some machines is not connected to earth ground
directly.
I suspect your MIG has one side of the transformer output connected to
earth ground. Then it goes thru the rectifier. Thus the "Ground"
clamp is fluctuating above and below earth ground by 15 volts or so,
with full current available. Check it with a voltmeter, "ground"
clamp to earth ground, and gun to earth ground.
I don't understand your three phase wiring.
If all three power legs were disconnected, (Assuming the lathe was
off.) I can see no way to melt a disconnected wire.
Dave J.
> Still machining a part for my cement mixer. =A0Needed to build up a 10" l=
ong
> shaft back to 3/4 inch diameter. =A0Thought I would put it in the lathe (=
1947=B1
> LeBlond Regal 13"), run a few beads over the necked down area with the MI=
G
> and then turn it down to size. =A0I just need to build up about a two inc=
h
> length near each end. =A0Anyway, did the above, turned on the lathe and i=
t
> doesn't work. =A0I have real 3-phase running the lathe, and a separate 24=
0
> 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. =A0The short was in the 6 foot long flex between the l=
athe
> and the 3-phase fused disconnect box. =A0I figured that maybe I had cramm=
ed
> too many wires (3-# 12's plus a bare ground) into the 1/2" flex and thing=
s
> got too hot. =A0It has served me for over 12 years. =A0Replaced it all wi=
th a
> 3/4" flex using #10 gauge (3 each plus ground). =A0This time, while using=
the
> MIG, I heard popping even before turning on the lathe. =A0The 3/4" flex w=
as
> warm and the wires melted therein.
>
> Okay, I'm smart enough that I won't be using my lathe as a welding fixtur=
e.
> BUT, what the =A0hell is going on. =A0Why would I create current in the l=
athe
> feed wires. =A0My ground clamp for the MIG was on the shaft within 2" of =
the
> weld. =A0BTW, both times it was the 'high' wire of the 3 phases that melt=
ed.
> Two of the wires carry 120 volts to ground each, and the third wire carri=
es
> more.
>
> All explanations appreciated. =A0Get to make up another feed for the old
> machine.
>
> Ivan Vegvary
|
|
Posted by Wild_Bill on September 9, 2008, 8:54 pm
Please log in for more thread options
I don't have the answer for the wiring failures, except that the wiring
isn't properly protected (for the gage/ampacity limits) to prevent them from
heating up. Fuses should blow, or circuit breakers should trip open before
the wiring has a chance to heat up.
Some meter testing between the two machines will show that there is a
significant voltage potential difference (possibly dangerous or fatal)
between them.
Have an electrician analyze the situation, in case there is a lethal fault,
and avoid it as you would a potentially dangerous electrical circuit.
You shouldn't get yourself into a situation where you could make body
contact with any two machines where one is 3-phase, and the other is single
phase until the wiring system is checked by a qualified, experienced
electrician.
The quickest solution would be to use a separate electrically isolated motor
to drive the lathe spindle, making sure that there is no electrical path
between the drive motor and the lathe.
This method would require a belt or insulated coupler between the motor
output shaft and the lathe spindle. No power applied to the lathe, the
additional motor (slow gearhead or belt/jackshaft speed reduction) is
driving the dead lathe as if it's just a fixture.
The reason for the electrical isolation would be to prevent any current path
thru the spindle bearings or other damage.
I would be sceptical of the ground clamp slipping on the workpiece shaft to
provide an adequate ground path, but it may work.
I'm fairly certain that others have tried it, and maybe you'll hear from
them.
I've contemplated fabricating a welding fixture with a variable speed
spindle for quite some time, and I can't imagine how desperate I'd have to
be to need to use a lathe as a welding fixture, but it's your machine.
It should be very clear that the existing setup that was tried at your
location would very likely destroy a VFD or possibly other electronic
devices, including the welder electronic circuitry.
WB
.........
metalworking projects
www.kwagmire.com/metal_proj.html
> 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
>
|
|
Posted by Ivan Vegvary on September 9, 2008, 9:08 pm
Please log in for more thread options
> 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
|
| Similar Threads | Posted | | Help with wiring of old lathe | May 10, 2006, 10:37 pm |
| Re: This Blew Me Away! | August 26, 2006, 10:09 pm |
| Blew up my logsplitter | October 14, 2009, 6:04 pm |
| Murphy was an Optimist.. Blew the 5914 Varidrive again... | May 31, 2008, 5:31 pm |
| shop wiring? | October 7, 2006, 10:06 am |
| Wiring for welder | August 11, 2007, 5:42 pm |
| Motor wiring help | September 26, 2007, 8:47 pm |
| help with rf-31 motor wiring | May 8, 2006, 7:49 am |
| AB 1305 Wiring ? | January 13, 2008, 6:27 pm |
| Wiring Ooooops | April 2, 2008, 5:23 am |
|
|
|
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap
>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.