Butt weld thoughts

More of an art than a science - discuss metalworking and welding here.



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PostPosted: Mon Aug 30, 2021 6:06 am
I don't do much mig welding, and don't really have an opinion on butt weld gap for mig welding. But I thought this first video was interesting because it goes against the accepted general opinion, it is dated 2014 and may have been updated, I don't know. Maybe someone has time to test gap-vs-no gap with perfectly straight cut coupons of some size, welded with no backer, to test for distortion difference.
https://youtu.be/vl_fZdRGTdg

This one might be interesting to some.
https://youtu.be/1vRmEu_5OBQ

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PostPosted: Mon Aug 30, 2021 8:32 am
:pcorn:
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PostPosted: Mon Aug 30, 2021 8:48 am
I liked that Last video

Gap, no Gap, I would say if your gonna use a Gap it should equal your wire thickness.
Just My opinion.
I myself wont use a Gap as a general rule, Not for thin sheet metal And personal only use a Mig on stuff thats impossible to get at with my Tig and or is a Lap weld or structural stuff. Mig does have its place.

Wire thickness - some like .023, I myself like .030 wire.
Some like ER70s-2 some like ER70s-3 I myself use ER70s-6 for general purpose uses and prefer ER70s-G for Auto sheet metal in general if I have to use a Mig.
Just like Gasses I know some guys that like Pure carbon dioxide and Some like a 70/30 mix I myself use an 80/20 mix.
Then theirs Trimming your Cup some like electrode where the wire comes out recessed inside the Cup I like it to Be flush.
Then their is Wire Stick out of the Wire some like 1/4" some like an 1/8" or some where in between.
Then theirs Torch angles and Pushing or Pulling the Puddle Their is no right or wrong really when it comes to Pushing or Pulling But they are two completely different techniques.

Welding - I think we can all agree "What works for one person doesn't work for all!"
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PostPosted: Mon Aug 30, 2021 5:41 pm
Doright wrote:I liked that Last video

Gap, no Gap, I would say if your gonna use a Gap it should equal your wire thickness.
Just My opinion.
I myself wont use a Gap as a general rule, Not for thin sheet metal And personal only use a Mig on stuff thats impossible to get at with my Tig and or is a Lap weld or structural stuff. Mig does have its place.

Wire thickness - some like .023, I myself like .030 wire.
Some like ER70s-2 some like ER70s-3 I myself use ER70s-6 for general purpose uses and prefer ER70s-G for Auto sheet metal in general if I have to use a Mig.
Just like Gasses I know some guys that like Pure carbon dioxide and Some like a 70/30 mix I myself use an 80/20 mix.
Then theirs Trimming your Cup some like electrode where the wire comes out recessed inside the Cup I like it to Be flush.
Then their is Wire Stick out of the Wire some like 1/4" some like an 1/8" or some where in between.
Then theirs Torch angles and Pushing or Pulling the Puddle Their is no right or wrong really when it comes to Pushing or Pulling But they are two completely different techniques.

Welding - I think we can all agree "What works for one person doesn't work for all!"


The video shows that when there is no gap there is no penetration on the back side of the weld.

As a newbie this is all so over whelming. I'm going to need to test gap vs. no gap myself and see what happens.



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PostPosted: Mon Aug 30, 2021 7:34 pm
They are not saying how thick those coupons are.
You have to pay attention as they also say with a Backing.

Thin auto sheet metal is a different animal compared to 1/16"-3/16" thick coupons.
Auto sheet metal is ruffly .047-.048 thick little more little less Generally speaking.

General rule with welding you need 1 amp per .001 thickness little more a little less depends on your technique and welder of choice. With a Tig I can get away with less.


https://www.youtube.com/watch?v=WuZYrLzPFwM
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A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.



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PostPosted: Thu Dec 02, 2021 11:24 am
wazzabie wrote:
The video shows that when there is no gap there is no penetration on the back side of the weld.

As a newbie this is all so over whelming. I'm going to need to test gap vs. no gap myself and see what happens.


Their are techniques for Back Purging back side of weld when using Zero gap.
With Tig welding its a Must in most all cases especially for Stainless and other exotic metals but not required for all welds.
With Mig It will make the Back side look a lot better but I would consider it advanced stuff for the novice. Would it Help Most defiantly in my opinion.

Check out this video about the subject. keep in mind that this subject metal is Stainless steel but effects are similar with mild steels.
https://www.youtube.com/watch?v=AIRWMhoke9I
Dennis Barnett
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.

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PostPosted: Sat Dec 04, 2021 4:15 pm
No problem with penetration of NO GAP patches with sheet metal. Once you get it set right the welds will easily bond the metal.

On thicker metal, you simply bevel the edge slightly which allows the weld to penetrate and fill the "V" you have created.
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PostPosted: Mon Dec 06, 2021 9:25 am
I try to get no gap when fitting up panels, as well. That video that shows that no gap fit ups have no penetration, is either for thick metals, or doing it wrong for 16, 18 or 20 ga. sheet metal!

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