Welding; How much undercut?

"Bruce A. Frank" wrote in
:

In a clusters there is a lot of heat build up necessary because so
much metal to draw the heat away. It is a good idea to switch to the
next larger diameter rod when welding clusters than when welding
single tube to single tube junctions. The larger filler rod helps to
suck a little of the heat away from the tube so that the tube doesn't
get so hot that undercut forms as you weld.

Undercut is a stress raiser, but in a standard truss-frame tube
fuselage built with 4130 there is a major overkill situation. The
tubes individually just aren't stress enough to lead to cracks where
there is minor undercut.

That said, I do not think you can allow any undercut in the firewall
structure which is holding the weight of the engine, or in the engine
mount itself. I would also avoid it in the landing gear structure.

If you have the tube up to the red heat level (gets that slight "wet"
look) then concentrating the heat on the filler letting the puddle
expand outward to incorporate the tube, you will accomplish a solid
weld with no cold lap. For the record, as much heat as is put into the
base metal when using an oxy/acet torch, cold lap is virtually
impossible. Not saying it can't be done, just not likely.


Thank you Bruce! As always, you are the man..

I went out and did a bit more. I had my welds pretty good a few years
ago and I went out determined to recapture that. Increasing the feed of
filler worked wonders and all signs of undercut are gone..
I think I was afraid of not getting the penetration I needed and was a
little too agressive with the puddle as well. At the moment,I'm getting
a nice bright glow from the parent edges just before the puddle runs
over them so I'm confident there's good penetration (confirmed with the
hacksaw) wheras before I was looking for a virtual lava river which was
obviously causing the undercut.

Welds are pretty good, but I am having one further problem; After a
minute or tow, my torch (a meco) often tends to go oxy, even though I
had it set right in the first place. Not a big problem once I spot it
early, but annoying al the same. It seems to stabilise after a while.
Could be that my acetylene tank is just running down, but I thought that
the regulators would cover that almost until the gas ran out.. Maybe I
need new regulators..

"Fortuant1" wrote

Thank you Bruce! As always, you are the man..

Yep; it's handy to have a welder man nearby, isn't it? :-)
--
Jim in NC

Fortuant1 wrote:


Welds are pretty good, but I am having one further problem; After a
minute or tow, my torch (a meco) often tends to go oxy, even though I
had it set right in the first place. Not a big problem once I spot it
early, but annoying al the same. It seems to stabilise after a while.
Could be that my acetylene tank is just running down, but I thought that
the regulators would cover that almost until the gas ran out.. Maybe I
need new regulators..


I had the Kent White set and the Medalist acet regulator would hunt and
surge and finally sent it back. Went out and bought another one locally
which seems to work well. His video is highly recommended.

I find the acet needs a few seconds to stablize any time there is an
adjustment on that side.

I have a Meco too and it is great, but seems to pop about as much as any
other torch. Welding 049 with a N-2 tip I had the gas turned way up and
it would still pop. May just be dirty.

Kent also includes and recommends E70 rod but it is terrible rod to gas
weld with and I switched to coat hanger to practice. Went out and got
some RG45 which is wonderful.

I can make more or less airworthy welds now, now working on making them
look nice. Things got a LOT easier once I learned the importance of
using the rod to help control the heat applied to the puddle so now I
almost never get burnaways. Still having to do a lot of stopping and
"adjusting", but about half the time now I can find that sweet spot
where the puddle is just right, the torch angle and heat is just right,
and I just have to move it along feeding the rod and the resulting bead
looks like a tig bead.

John

"J.Kahn" wrote in message
. ..
Fortuant1 wrote:


Welds are pretty good, but I am having one further problem; After a
minute or tow, my torch (a meco) often tends to go oxy, even though I had
it set right in the first place. Not a big problem once I spot it early,
but annoying al the same. It seems to stabilise after a while. Could be
that my acetylene tank is just running down, but I thought that the
regulators would cover that almost until the gas ran out.. Maybe I need
new regulators..

I had the Kent White set and the Medalist acet regulator would hunt and
surge and finally sent it back. Went out and bought another one locally
which seems to work well. His video is highly recommended.

I find the acet needs a few seconds to stablize any time there is an
adjustment on that side.

I have a Meco too and it is great, but seems to pop about as much as any
other torch. Welding 049 with a N-2 tip I had the gas turned way up and
it would still pop. May just be dirty.

Kent also includes and recommends E70 rod but it is terrible rod to gas
weld with and I switched to coat hanger to practice. Went out and got
some RG45 which is wonderful.

I can make more or less airworthy welds now, now working on making them
look nice. Things got a LOT easier once I learned the importance of
using the rod to help control the heat applied to the puddle so now I
almost never get burnaways. Still having to do a lot of stopping and
"adjusting", but about half the time now I can find that sweet spot where
the puddle is just right, the torch angle and heat is just right, and I
just have to move it along feeding the rod and the resulting bead looks
like a tig bead.

John

Hi John,

If you have a lot of problems with a torch popping, try running a little
less OX. From a perfect appearing burn, you should richen the mix just
enough to produce a little bit of feather. Maybe a 1/4 to 1/2" will usually
make a world of difference.

Maxwell wrote:
"J.Kahn" wrote in message
. ..
Fortuant1 wrote:

Welds are pretty good, but I am having one further problem; After a
minute or tow, my torch (a meco) often tends to go oxy, even though I had
it set right in the first place. Not a big problem once I spot it early,
but annoying al the same. It seems to stabilise after a while. Could be
that my acetylene tank is just running down, but I thought that the
regulators would cover that almost until the gas ran out.. Maybe I need
new regulators..
I had the Kent White set and the Medalist acet regulator would hunt and
surge and finally sent it back. Went out and bought another one locally
which seems to work well. His video is highly recommended.

I find the acet needs a few seconds to stablize any time there is an
adjustment on that side.

I have a Meco too and it is great, but seems to pop about as much as any
other torch. Welding 049 with a N-2 tip I had the gas turned way up and
it would still pop. May just be dirty.

Kent also includes and recommends E70 rod but it is terrible rod to gas
weld with and I switched to coat hanger to practice. Went out and got
some RG45 which is wonderful.

I can make more or less airworthy welds now, now working on making them
look nice. Things got a LOT easier once I learned the importance of
using the rod to help control the heat applied to the puddle so now I
almost never get burnaways. Still having to do a lot of stopping and
"adjusting", but about half the time now I can find that sweet spot where
the puddle is just right, the torch angle and heat is just right, and I
just have to move it along feeding the rod and the resulting bead looks
like a tig bead.

John

Hi John,

If you have a lot of problems with a torch popping, try running a little
less OX. From a perfect appearing burn, you should richen the mix just
enough to produce a little bit of feather. Maybe a 1/4 to 1/2" will usually
make a world of difference.


Thanks

I usually set it with a tiny bit of carb showing, just enough to soften
the neutral cone edge. Are you saying a 1/4" to 1/2" long carburizing
feather is ok?

And I think my problem was the N-2 tip was a bit too big because the
pieces are small and heat isn't sinking away. I just tried an N-1 tip
nearly maxed out and it put out enough heat for a full puddle and no
pops. This seems to be one of those borderline conditions where the
best tip would be in between N-1 and N-2.

I still have to get a 0 tip and a 0 tip drilled to about 0 and a half
for doing .028 and .035.

Cheers

John

"J.Kahn" wrote in message
. ..
Maxwell wrote:
"J.Kahn" wrote in message
. ..
Fortuant1 wrote:

Welds are pretty good, but I am having one further problem; After a
minute or tow, my torch (a meco) often tends to go oxy, even though I
had it set right in the first place. Not a big problem once I spot it
early, but annoying al the same. It seems to stabilise after a while.
Could be that my acetylene tank is just running down, but I thought
that the regulators would cover that almost until the gas ran out..
Maybe I need new regulators..
I had the Kent White set and the Medalist acet regulator would hunt and
surge and finally sent it back. Went out and bought another one locally
which seems to work well. His video is highly recommended.

I find the acet needs a few seconds to stablize any time there is an
adjustment on that side.

I have a Meco too and it is great, but seems to pop about as much as any
other torch. Welding 049 with a N-2 tip I had the gas turned way up and
it would still pop. May just be dirty.

Kent also includes and recommends E70 rod but it is terrible rod to gas
weld with and I switched to coat hanger to practice. Went out and got
some RG45 which is wonderful.

I can make more or less airworthy welds now, now working on making them
look nice. Things got a LOT easier once I learned the importance of
using the rod to help control the heat applied to the puddle so now I
almost never get burnaways. Still having to do a lot of stopping and
"adjusting", but about half the time now I can find that sweet spot
where the puddle is just right, the torch angle and heat is just right,
and I just have to move it along feeding the rod and the resulting bead
looks like a tig bead.

John

Hi John,

If you have a lot of problems with a torch popping, try running a little
less OX. From a perfect appearing burn, you should richen the mix just
enough to produce a little bit of feather. Maybe a 1/4 to 1/2" will
usually make a world of difference.


Thanks

I usually set it with a tiny bit of carb showing, just enough to soften
the neutral cone edge. Are you saying a 1/4" to 1/2" long carburizing
feather is ok?

It shouldn't require an actual 1/2" to eliminate the popping problem, and
you shouldn't add more than necessary to stop the torch from popping. But
often when popping is a problem, you are running just a bit to lean. It
will also cool that N-2 tip down just a bit.

70s-6 is a better choice than 45.

"J.Kahn" wrote: Fortuant1 wrote:


  Welds are pretty good, but I am having one further problem; After a
minute or tow, my torch (a meco) often tends to go oxy, even though I
had it set right in the first place. Not a big problem once I spot it
early, but annoying al the same. It seems to stabilise after a while.
Could be that my acetylene tank is just running down, but I thought that
the regulators would cover that almost until the gas ran out.. Maybe I
need new regulators..


I  had the Kent White set and the Medalist acet regulator would hunt and
surge and finally sent it back.  Went out and bought another one locally
which seems to work well.    His video is highly recommended.

I find the acet needs a few seconds to stablize any time there is an
adjustment on that side.

I have a Meco too and it is great, but seems to pop about as much as any
other torch.  Welding 049 with a N-2 tip I had the gas turned way up and
it would still pop.   May just be dirty.

Kent also includes and recommends E70 rod but it is terrible rod to gas
weld with and I switched to coat hanger to practice.   Went out and got
some RG45 which is wonderful.

I can make more or less airworthy welds now, now working on making them
look nice.   Things got a LOT easier once I learned the importance of
using the rod to help control the heat applied to the puddle so now I
almost never get burnaways.  Still having to do a lot of stopping and
"adjusting", but about half the time now I can find that sweet spot
where the puddle is just right, the torch angle and heat is just right,
and I just have to move it along feeding the rod and the resulting bead
looks like a tig bead.

John

--
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