TIG pits in clean 16 ga steel

[short arc]

New wanna be weldor here.
I have new, clean 16 gauge steel cleaned with acetone and a new SS brush. I am using new 1/16" electrodes at 40A as close to vertical as I can get, 25 CFM argon on a Miller 250 DX. I amaze myself with a nice butt weld for 1/2" then there is a sputter with a pit and stuff on the electrode. The electrode is not sticking to the steel. Standoff is 1/4" to 3/8". The sheet steel is supported on 4 " C channel. I grind out the weld and use .035 MIG wire cleaned with acetone to fill in the pits. Should I have back purge? How do I prevent this pitting??????
Note: I did search on tig pitting but my google-fu must not be strong......
Thanks!
Jim

[short arc]

I forgot to add that I tack every 1/2" on an 18" run. I wait for the tack to cool before doing the next one. The fit up is tight and the tacks show bright, shiny metal with no oxides on the weld side with a 9 sec post purge. The pits seem to be unrelated to the tacks. This is my first attempt at a shifter pedestal for a rock crawlin' jeep for a buddy.
Best,
Jim

[CAVEMANN]

Sorry I can't help, but sometimes life is the "pits".

[MinnesotaDave]

Are you using filler metal during the regular weld, or just when you hit a problem?

Steel welds nicer with filler in my opinion.

If by "standoff" you meant the distance of tungsten to steel, that's way too long of an arc.

Is the channel nice and clean, no rust or paint?

Aluminum is a better backer for thin steel.

Pics generally help a lot.

[shovelon]

Firstly, I gotta ask for your 25cfh argon flow what kind and size of cup are you using? My shop formula is 2 to 3 times the cup size with 2.5 times the cup size to start. So 25cfh would put me in a #8 cup or bigger. Catch my drift?

Secondly I agree with MinnesotaDave, you need to keep your arc length(standoff) toight. That means to me 1/8" or less. Figure whatever your tungsten diameter would be your standoff. A 3/32 tungsten would be 3/32. A 1/8th tungsten would be 1/8" standoff.

The combo of too rapid velocity of gas stream, and long standoff like 3/8" could be pulling air onto your weld causing contamination and your troubles.

Also your amps is pretty low to me. With the "rule of thumb" of 1 amp per .001" your amps would help move you along if you were 60 amps or more. I by default set my amps at 100 for 16 gauge steel, and float the pedal as required. Then on start punch the pedal for a hot fast puddle, drive the melt thru and cram the rod to fill the puddle then jam forward and repeat. Time is your enemy.

Lots to think about but it will all come together.

[short arc]

Are you using filler metal during the regular weld, or just when you hit a problem?

Steel welds nicer with filler in my opinion.

If by "standoff" you meant the distance of tungsten to steel, that's way too long of an arc.

Is the channel nice and clean, no rust or paint?

Aluminum is a better backer for thin steel.

Pics generally help a lot.

Dave,
Thanks for the advice.
I understand that the arc is too long and will use a shorter arc.
The channel is clean and the contact areas are far from where the welding is done.
That is, there is only air behind the steel.
Soon as I figure out how to post fotos after Memorial Day, I will.
Best regards,
Jim

[short arc]

Firstly, I gotta ask for your 25cfh argon flow what kind and size of cup are you using? My shop formula is 2 to 3 times the cup size with 2.5 times the cup size to start. So 25cfh would put me in a #8 cup or bigger. Catch my drift?

Secondly I agree with MinnesotaDave, you need to keep your arc length(standoff) toight. That means to me 1/8" or less. Figure whatever your tungsten diameter would be your standoff. A 3/32 tungsten would be 3/32. A 1/8th tungsten would be 1/8" standoff.

The combo of too rapid velocity of gas stream, and long standoff like 3/8" could be pulling air onto your weld causing contamination and your troubles.

Also your amps is pretty low to me. With the "rule of thumb" of 1 amp per .001" your amps would help move you along if you were 60 amps or more. I by default set my amps at 100 for 16 gauge steel, and float the pedal as required. Then on start punch the pedal for a hot fast puddle, drive the melt thru and cram the rod to fill the puddle then jam forward and repeat. Time is your enemy.

Lots to think about but it will all come together.

Shovelon,

Ack, I am using #6 with a gas lens. #8s and gas lenses are on order.
I am using a 1/16 dia tungsten for 16 ga steel. I thought that a smaller tungsten and 40 A = less heat distortion????
Understood about 100 A, floating the pedal and moving fast.
Since I have not tigged thin sheet steel before, I had tried to limit heat distortion.
Do you recommend doing about an inch at a time, back stepping for an 18" run?
The panel beaters had recommended staying away from filler rod to minimize grinding / sanding / warpage.
I don't have their skill (yet, ).
Sounds like I need to change my game any way.
Thank you for the advice.
Fotos to follow after Memorial Day.
Best,
Jim

[Oscar]

Shovelon,

Ack, I am using #6 with a gas lens. #8s and gas lenses are on order.
I am using a 1/16 dia tungsten for 16 ga steel. I thought that a smaller tungsten and 40 A = less heat distortion????
Understood about 100 A, floating the pedal and moving fast.
Since I have not tigged thin sheet steel before, I had tried to limit heat distortion.
Do you recommend doing about an inch at a time, back stepping for an 18" run?
The panel beaters had recommended staying away from filler rod to minimize grinding / sanding / warpage.
I don't have their skill (yet, ).
Sounds like I need to change my game any way.
Thank you for the advice.
Fotos to follow after Memorial Day.
Best,
Jim

25 CFH with a #6 gas lens?!?! where did you read to use that much?!? lol. 12-15 CFH with 1/4" stickout, and no more than 1/8" actual arc length, to start off with. 1/16" tungsten will work, but it doesn't do anything for heat distortion, as that is dependent on heat input, which is not as simple as it sounds.

[MinnesotaDave]

Shovelon,

Ack, I am using #6 with a gas lens. #8s and gas lenses are on order.
I am using a 1/16 dia tungsten for 16 ga steel. I thought that a smaller tungsten and 40 A = less heat distortion????
Understood about 100 A, floating the pedal and moving fast.
Since I have not tigged thin sheet steel before, I had tried to limit heat distortion.
Do you recommend doing about an inch at a time, back stepping for an 18" run?
The panel beaters had recommended staying away from filler rod to minimize grinding / sanding / warpage.
I don't have their skill (yet, ).
Sounds like I need to change my game any way.
Thank you for the advice.
Fotos to follow after Memorial Day.
Best,
Jim

Avoiding filler with thin sheet is only possible with near perfect fit up.
Zero filler will generally leave the weld thinner than the parent material.

Low amps makes for slow travel speed, which increases overall heat input.

In the heat input formula, travel speed is in the denominator, therefore more speed equals less overall heat input.
To achieve more speed, more amps must be used.

[Go1lum]

Avoiding filler with thin sheet is only possible with near perfect fit up.
Zero filler will generally leave the weld thinner than the parent material.

Low amps makes for slow travel speed, which increases overall heat input.

In the heat input formula, travel speed is in the denominator, therefore more speed equals less overall heat input.
To achieve more speed, more amps must be used.

Yup heat input is (Voltage X Amperage x 60sec/min)/travel speed which gives your joules per inch